Recent Advances on the Chemistry of Transition Metal Complexes with Monoanionic Bidentate Silyl Ligands

Abstract

The chemistry of transition‐metal (TM) complexes with monoanionic bidentate (κ²‐L,Si) silyl ligands has considerably grown in recent years. This work summarizes the advances in the chemistry of TM‐(κ²‐L,Si) complexes (L=N‐heterocycle, phosphine, N‐heterocyclic carbene, thioether, ester, silylether or tetrylene). The most common synthetic method has been the oxidative addition of the Si−H bond to the metal center assisted by the coordination of L. The metal silicon bond distances in TM‐(κ²‐L,Si) complexes are in the range of metal‐silyl bond distances. TM‐(κ²‐L,Si) complexes have proven to be effective catalysts for hydrosilylation and/or hydrogenation of unsaturated molecules among other processes.

Full text

Recent Advances on the Chemistry of Transition Metal
Complexes with Monoanionic Bidentate Silyl Ligands
María Batuecas,*[a] Alejandra Goméz-España,[a, b] and Francisco J. Fernández-Álvarez*[a]
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doi.org/10.1002/cplu.202400162

The chemistry of transition-metal (TM) complexes with mono-
anionic bidentate (k2-L,Si) silyl ligands has considerably grown
in recent years. This work summarizes the advances in the
chemistry of TM-(k2-L,Si) complexes (L=N-heterocycle,
phosphine, N-heterocyclic carbene, thioether, ester, silylether or
tetrylene). The most common synthetic method has been the
oxidative addition of the SiH bond to the metal center assisted
by the coordination of L. The metal silicon bond distances in
TM-(k2-L,Si) complexes are in the range of metal-silyl bond
distances. TM-(k2-L,Si) complexes have proven to be effective
catalysts for hydrosilylation and/or hydrogenation of unsatu-
rated molecules among other processes.
1. Introduction
One of the foundations of homogeneous catalysis based on
transition metal (TM) complexes is that by adjusting the
electronic and/or steric properties of the ligands “ligand tuning”
it is possible to optimize both the activity and the selectivity of
the catalytic processes. That is why the design and develop-
ment of ligands can be considered one of the most important
research topics within homogeneous catalysis.[1]
In this context, the chemistry of TM-complexes with multi-
dentate organosilyl ancillary ligands have considerably grown
in the last decades.[2–8] These type of ligands are characterized
by their strong σ-donor character, and the high trans-effect and
-influence of the silyl group which facilitate the generation of
electronically and coordinatively unsaturated species.[2–8]
TM-complexes with tetradentate k4-L3,Si,[7] tridentate k3-
L2,Si,[4,5,8] and/or bidentate k2-L,Si[6] ligands, where Si symbolizes
a silyl group and L represents a σ-donor ligand (N-heterocycle,
phosphine, N-heterocyclic carbene, thioether, ester, silylether or
tetrylene), have been reported. Most of the studies on TM-
complexes with multidentate silyl ancillary ligands published to
date are focused on the chemistry of species with tridentate
ligands of type k3-L,Si,L, which have been the subject of
numerous reviews in recent years.[4,5,8] The chemistry of TM-
complexes with monoanionic bidentate k2-L,Si ligands has
gained interest in recent years due to their potential as
hydrosilylation and hydrogenation homogeneous catalysts.
Moreover, some TM-(k2-L,Si) complexes have shown better
catalytic performance than their TM-(k3-L,Si,L) counterparts in
CO2hydrosilylation and Kumada coupling reactions. This review
describes the recent outcomes of the chemistry of TM-
complexes with different k2-L,Si ligands including their synthesis
and applications in homogeneous catalysis, as well as some
relevant aspects about the nature of the metalSi bond
(Figure 1).
This review has been organized into sections in which the
ligands have been classified based on the nature of the σ-donor
atom (E in Figure 1). In each section, the methodology of
synthesis of the ligands and the corresponding complexes are
described, as well as some relevant aspects about the structure,
reactivity, and catalytic activity. In addition, a final brief
discussion about the metal-silicon bond distances in TM-(k2-L,Si)
species has also been included.
2. Transition Metal Complexes with k2-L,Si
Ligands
2.1. Transition Metal Complexes with k2-N,Si Ligands
To the best of our knowledge the first example of a TM-(k2-N,Si)
complex was reported in 1989 by Ang and Kwik. They prepared
the complex [Re(k2-N,Si-L1)(CO)4] (L1 =2-pyridyldimethylsilyl, 1)
by reaction of 2-pyridyldimethylsilane with [Re(CO)5]2at 433 K.
Complex 1was characterized by means of elemental analysis
and infrared spectroscopy (Scheme 1).[9]
Some years later, Watts and collaborators reported the
synthesis and characterization of rhodium- and iridium-(k2-N,Si)
[a] Dr. M. Batuecas, Dr. A. Goméz-España, Prof. Dr. F. J. Fernández-Álvarez
Departamento de Química Inorgánica – Instituto de Síntesis Química y
Catálisis Homogénea (ISQCH)
Universidad de Zaragoza -CSIC
Facultad de Ciencias, Plaza de San Francisco, 50009, Zaragoza, Spain
E-mail: mbatuecas@unizar.es
paco@unizar.es
[b] Dr. A. Goméz-España
Centro de Investigación e Innovación Educativas (CIIE)
Universidad Pedagógica Nacional Francisco Morazán-UPNFM
Tegucigalpa, 11101, Honduras.
© 2024 The Authors. ChemPlusChem published by Wiley-VCH GmbH. This is
an open access article under the terms of the Creative Commons Attribution
Non-Commercial NoDerivs License, which permits use and distribution in
any medium, provided the original work is properly cited, the use is non-
commercial and no modifications or adaptations are made.
Figure 1. General representation of TM-complexes with k2-L,Si ligands.
Scheme 1. Synthesis of the complex [Re(k2-N,Si-L1)(CO)4] (1).
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complexes with 8-quinolyldimethylsilyl based ligands
(Scheme 2).[10] Thus, the reaction of 8-(dimethylsilyl)quinoline
with [{M(cod)}2(μ-Cl)2] (M=Rh or Ir; cod=1,5-cyclooctadiene) in
refluxing ethanol affords the corresponding species [M(Cl)(k2-
N,Si-L2)2] (L2 =(8-quinolyl)dimethylsilyl; M=Rh, 2; Ir, 3). The
solvent matters, thus when the reaction with [{Ir(cod)}2(μ-Cl)2]
was set up in refluxing 2-ethoxyethanol the octahedral Ir(III)
complex [Ir(Cl)(k2-N,Si-L2)2(CO)] (4) was obtained.[10a]
The same group reported that using the complexes [M-
(H)(PPh3)3(CO)] (M=Rh, Ir) as metallic precursors and toluene as
solvent, the coordination of three ligand units to generate the
corresponding fac-[M(k2-N,Si-L2)3] (M=Rh, 5; Ir, 6) species takes
place (Scheme 3).[10a,b] This methodology has been used success-
fully to prepare a number of fac-[M(k2-N,Si-Ln)3] species (Ln =
L3, (6-isopropyl-8-quinolyl)dimethylsilyl, M=Rh, 7; Ir, 8;Ln =L4,
(6-isopropyl-8-quinolyl)phenylmethylsilyl, M=Rh, 9; Ir, 10; and
Ln =L5 (6-isopropyl-8-quinolyl)diphenylsilyl, M=Rh, 11; Ir, 12),
which stand out for their interesting optical properties.[10] The
metalSi bond distances in complexes 5(2.278(1), 2.290(1) and
2.301(1) Å) and 6(2.296(4), 2.301(4) and 2.305(4) Å)[10b] are
shorter than should be expected for a Rhor Irsilyl bond.[2b,c,d]
Yoshizawa, Nishibayashi et al. reported in 2015 the synthesis
of the related Co(III) species [Co(k2-N,Si-L6)3] (13) (L6 =2-
(dimethylsilyl)methylpyridine) by reaction of [Co(H)(N2)(PPh3)3]
with the corresponding functionalized silane in THF at room
temperature (r.t.). Complex 13 was characterized by 1H and 13C
NMR spectroscopy and X-ray diffraction analysis, the CoSi
bond distances in 13 are in the range of 2.2311(8)–2.2424(9) Å
(Scheme 4).[11]
María Batuecas received her degree in
Chemistry at the University Complutense of
Madrid. Then, she studied her PhD in Organo-
metallic Chemistry in Zaragoza under the
supervision of Prof. Esteruelas and Dr. García-
Yebra. Upon graduating, she joined Prof.
Larrosa group at the University of Manchester
(MSCA fellowship). Following a postdoc with
Prof. Fernández (Almeria), she returned to the
UK as a postdoc in the Prof. Crimmin group.
Currently, she is back at University of Zaragoza
working in collaboration with Prof. Fernández-
Alvarez as MSCA-Cofund fellow. Her research
interest focuses on the design synthesis, and
study of new transition-metal and main group
complexes.
Alejandra Gómez-España is Associate Profes-
sor at the Centro de Investigación e Innova-
ción Educativa of the Universidad Pedagogica
Nacional Francisco Morazán -(UPNFM). She
completed her master's degree (M.Sc.) in
Educational Chemistry at the UPNFM in Teg-
ucigalpa (Honduras) in 2017. In 2020, she
moved to the University of Zaragoza (España)
where she recieved the PhD degree in
Chemistry in 2023 under the supevision of
Prof. Fernander-Alvarez and Dr. Iglesias. Her
PhD thesis was focused on the developmet of
Rh and Ir catalysts with k2-N,Si ligands.
Francisco J. Fernández-Álvarez is Professor
Titular at the University of Zaragoza (España).
He received his PhD in Chemistry at the
University of Alcalá (Madrid, 1999) in Prof.
Royo's group. He did postdoctoral stays at the
Universities of Zurich (Prof. Berke) and Zarago-
za (Prof. Esteruelas). He began his independ-
ent career at the University of Zaragoza (2011)
in collaboration with Prof. Oro and Prof. Perez-
Torrente. He has studied the chemistry of Rh
and Ir complexes with tri- and bidentate
organosilyl ligands and their potential as
homogeneous catalysts for CO2and small
molecules activation, field in which he is co-
author of several publications.
Scheme 2. Synthesis of complexes [M(Cl)(k2-N,Si-L2)2] (M=Rh, 2; Ir, 3) and
[Ir(Cl)(k2-N,Si-L2)2(CO)] (4). Scheme 3. Synthesis of complexes [M(k2-Si,N-Ln)3] (Ln =L2,L3,L4 and L5).
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Huertos et al. have been protagonists in the recent
emergence of the chemistry of rhodium with 8-quinolyl based
and related k2-N,Si ligands,[12,13] focusing on the synthesis of
unsaturated species and on the study of their catalytic
applications. Thus, they recently prepared the 16-electron
cationic species [Rh(k2-N,Si-L2)2(NCMe)][BArF4] (14) (BArF4=
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)by reaction of 2
with Na[BArF4] in CH2Cl2/ acetonitrile. Compound 14 reacts with
bipyridine to give the saturated cationic species [Rh(k2-N,Si-
L2)2(bipy)][BArF4] (15) (Scheme 5).[12]
Moreover, using this methodology, they were able to
prepare the unsaturated 14-electron species [Rh(k2-N,Si-
Ln)2][BArF4] (Ln =L7, 8-(dimethylsilyl)-2-methylquinoline, 16;
Ln =L8, (9-phenyl-4-acridyl)dimethylsilyl, 17) (Scheme 6).[12]
NBO and QTAIM analysis of complexes 16 and 17, revealed that
agostic interactions Rh···HC are present in both compounds. In
addition, it should be mentioned that the RhSi bond distances
in 2(2.2571(6) Å; 2.2500(6) Å), 16 (2.2746(7) Å; 2.2654(8) Å) and
17 (2.2573(8) Å; 2.2498(8) Å) are shorter than should be
expected for a Rhsilyl bond.[2b,c,d] Complexes 16 and 17 have
proven to be highly effective catalysts for the selective
hydrolysis of diphenylsilane.
Huertos et al. have also reported that using [Rh(Cl)(PPh3)3]
as rhodium precursor it is possible to prepare Rh-(k2-N,Si)
complexes containing only one k2-(N,Si) ligand. Thus, the
reaction of 8-(dimethylsilyl)quinoline, 8-(dimethylsilyl)-2-methyl-
quinoline and 4-(dimethylsilyl)-9-phenylacridine with [Rh-
(Cl)(PPh3)3] in CH2Cl2affords the corresponding species [Rh-
(H)(Cl)(k2-N,Si-Ln)2(PPh3)] (Ln =L2,18;Ln =L7,19; and Ln =L8,
20), which react with Na[BArF4] in CH2Cl2to give the correspond-
ing cationic species [Rh(H)(k2-Ln)(PPh3)2][BArF4] (Ln =L2,21;
Ln =L7,22; and Ln =L8,23) (Scheme 7).[13] The RhSi bond
distance in the neutral species 19 (2.2635(7) Å) is shorter than
that found for 22 (2.2985(9) Å). The cationic species 21,22, and
23 are active catalysts for the hydrosilylation of remote alkenes
to give the corresponding lineal organosilane, the best catalytic
Scheme 4. Synthesis of the complex [Co(k2-N,Si-L6)3] (13).
Scheme 5. Synthesis of the Rh-(k2-N,Si) cationic species 14 and 15.
Scheme 6. Synthesis of the 14-electron unsaturated Rh-(k2-N,Si) cationic
species 16 and 17.
Scheme 7. Synthesis of the Rh-(k2-N,Si) species 18,19,20,21,22 and 23.
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performance was achieved using complex 21 as catalyst
precursor.[13]
Komuro, Hashimoto and collaborators have recently re-
ported the synthesis of M-(k3-N,N,Si-L9) (M =Rh, Ir) complexes
with the tridentate ligand 2-(ditertbutylsilyl)methyl-1,8-naphtyr-
idine) (L9).[14] They have also reported the synthesis of rhodium
and iridium complexes in which L9 acts as bidentate k2-N,Si
ligand.[15] Thus, the reaction of the proligand L9-H with
[{Rh(coe)2}2(μ-Cl)2] (coe=cis-cyclooctene) affords the dinuclear
complex [{Rh(H)(k2-N,Si-L9)}2(μ-Cl)2] (24), which reacts with
excess of BH3-SMe2to afford the mononuclear BH3adduct
[Rh(H)(Cl){k4-Si,N,H,H,-L9-(BH3)}] (25) (Scheme 8).[15a] The RhSi
bond distances in 24 (2.2648(4) Å and in 25 (2.2990(8) Å)
compare to those found for complexes 19 and 22.
The proligand L9-H reacts with [{Ir(coe)2}2(μ-Cl)2] to give the
iridium(III) complex [Ir(H)(Cl)(k2-N,Si-L9)(coe)] (26), which reacts
with DABAL-Me3(Bis(trimethylaluminum)-1,4-
diazabicyclo[2.2.2]octane adduct, (AlMe3)2-DABCO) to afford the
Ir-methyl complex [Ir(H)(CH3)(k2-N,Si-L9)](coe)] (27). 1H NMR
studies of the reaction of 27 with H2(1 atm) and PCy3evidenced
the formation of the Ir(V) tetrahydride [Ir(H4)(k2-N,Si-L9)](PCy3)
(28), which was characterized in solution by means of multi-
nuclear NMR spectroscopy (Scheme 9).[15b] Complexes 26 and 27
were also characterized by X-ray diffraction, the IrSi bond
distances for these complexes are 2.3016(10) Å and 2.2887(14)
Å, respectively.[15b] Same authors have also reported the syn-
thesis of the related iridium(III) species [Ir(H)(Cl)(k2-N,Si-
L10)(coe)] (29) and [Ir(H)(CH3)(k2-N,Si-L10)(coe)] (30) (L10 =2-
(ditertbutylsilyl)methyl-6-methyl-pyridine) (Scheme 9). The Ir-
methyl derivatives 27 and 30 are effective catalytic precursors
for hydrogenation of olefins. However, the activity of 27 is
higher than that found for 30, which proves the relevance of
the nitrogen lone pair of 27 on the catalytic activity. Thus, the
authors have proposed that in the case of 27-catalyzed hydro-
genation of alkenes, the H2activation could occur through a
cooperative Lewis acid/base process between the nitrogen and
the metal center.[15b]
Another type of N,Si bidentate ligands are those based on
2-pyridones. To the best of our knowledge, first examples of a
TM-complex with a 2-pyridone based ligand were the iron
species [Fe(η5-C5R5)(k2-N,Si-L11)(CO)] (L11 =(pyridine-2-
yloxy)dimethysilyl; R=H, 31; Me, 32) reported by Tobita and
collaborators.[16] The Fe-(k2-N,Si) complexes 31 and 32 where
obtained by photolysis of the precursor [Fe(η5-C5R5)(k1-Si-
L11)(CO)2] or by irradiation of complex [Fe(η5-C5R5)(CO)2(SiMe3)]
in the presence of proligand L11-H (Scheme 10).[16]
Scheme 8. Synthesis of the Rh-(k2-N,Si) complexes 24 and 25.
Scheme 9. Synthesis of the Ir-(k2-N,Si)26,27,28,29 and 30.
Scheme 10. Synthesis of the Fe-(k2-N,Si) complexes 31 and 32.
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Same group has also reported examples of Mo and W
complexes with k2-N,Si ligands. Compounds [M(η5-C5Me5)(k2-
N,Si-L12)(CO)2] (L12 =(pyridine-2-yloxy)bisparatolylsilyl; M=Mo,
33; W, 34) were prepared by reaction of η3-α-silabenzenyl
species [M(η5-C5Me5){k3-(Si,C,C)-Si(p-Tol)3}(CO)2] (M=Mo, W)
with 2-hydroxypyridine (Scheme 11).[17]
Roper, Wright et al. reported the preparation of Ru-(k2-N,Si)
complexes by nucleophilic substitution reaction of the SiCl
bond in [Ru(SiClPh2)(k2-S2CNMe2)(CO)(PPh3)2]. Thus, reaction of
Ru-(k2-S2CNMe2) precursor with 2-hydroxypyridine and 2-amino-
pyridine affords the corresponding species [Ru(k2-N,Si-L13)(k2-
S2CNMe2)(CO)(PPh3)] (L13 =(pyridine-2-yloxy)bisphenylsilyl, 35)
and [Ru(k2-N,Si-L14)(k2-S2CNMe2)(CO)(PPh3)] (L14 =N-
(diphenylsilyl)pyridine-2-amine, 36), respectively (Scheme 12).[18]
The RuSi bond distances found for 35 (2.3487(4) Å) and 36
(2.3400(7) Å) are in the expected range for Ru-silyl
complexes.[2b,c,d]
Iridium complexes with 4-methylpyridin-2-yloxy-dimethylsil-
yl (L15),[19] 4-methylpyridin-2-yloxy-diisopropylsilyl (L16),[20] and
4-methylpyridin-2-yloxy-ditertbutylsilyl (L17)[21] ligands have
been prepared by reaction of the corresponding pyridine-2-
yloxy-silane derivative with [{Ir(coe)2}2(μ-Cl)2]. The bulkiness of
the substituents at the silicon atom of the k2-N,Si ligand
strongly influences the nature of the reaction products. Thus, in
iridium(III) complexes with k2-N,Si-L15[19] and k2-N,Si-L16[20]
ligands the coordination of two ligand units to the metal center
to give the corresponding species [{Ir(k2-N,Si-L15)2}2(μ-Cl)2]
(37)[19] or [Ir(Cl)(k2-N,Si-L16)2] (38)[20] respectively, is favored.
However, when using L17-H proligand, which contains tertbu-
tyl, instead of methyl or isopropyl substituents, the coordination
of only one ligand unit to the metal center, to give the complex
[Ir(H)(Cl)(k2-N,Si-L17)(coe)] (39) is observed (Scheme 13).[21]
The reaction of 37 and/or 38 with one equivalent of
Ag(O2CCF3) (AgTFA) quantitatively affords the corresponding
iridium-trifluoroacetate derivative [Ir(k2-O2CCF3)(k2-N,Si-L15)2]
(40)[19] and [Ir(k2-O2CCF3)(k2-N,Si-L16)2] (41).[20] The nature of the
reaction product obtained from the reaction of 37 and/or 38
with Ag(OSO2CF3) (AgOTf) depends on the substituents at the
silicon atom. Thus, while the reaction of 37 with one equivalent
of AgOTf per iridium gives the dinuclear species [{Ir(k2-N,Si-
L15)2}2(μ-OTf)2] (42),[22] under the same conditions the reaction
of 38 with AgOTf affords the mononuclear complex [Ir(k1-O-
OTf)(k2-N,Si-L15)2] (43) (Scheme 14).[20] To the best of our
knowledge, complex 42 is the first example of an iridium
species with triflate ligands acting as bridge.
Scheme 11. Synthesis of the complexes Mo-(k2-N,Si) (33) and Mo-(k2-N,Si)
(34).
Scheme 12. Synthesis of the Ru-(k2-N,Si) complexes 35 and 36.
Scheme 13. Synthesis of the Ir-(k2-N,Si) complexes 37,38 and 39.
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The iridium species 40 has proven to be an effective
catalysts for the selective reduction of CO2with silanes to the
formate (4 bar of CO2) or methoxy (1 bar of CO2) level.[19]
Moreover, when the catalytic system 40/B(C6F5)3was used as
catalyst for the reaction of CO2(1 bar) with hydrosilanes, the
corresponding bis(silyl)acetal, CH2(OSiR3)2, was selectively
obtained.[23] The ancillary ligand also plays a key role in the
selectivity of these catalytic processes, thus when the triflate
derivative 42 was used as catalyst for the reduction of CO2with
hydrosilanes mixtures of the corresponding silylformate, me-
thoxysilane and methylsilylcarbonate (MeOC(O)-OSiR3) were
obtained.[22] It should be noted that the Ir-(k2-N,Si) species 40
has a better catalytic performance than related Ir-fac-(k3-N,Si,N)
catalysts. The lower activity of Ir-fac-(k3-N,Si,N) species has been
attributed to the steric hindrance and rigidity of the tridentate
ligands.[24]
The proligand L15-H has also been succesfully used to
prepare rhodium complexes. Thus, the reaction of L15-H with
[{Rh(coe)2}2(μ-Cl)2] affords the mononuclear rhodium(III) species
[Rh(Cl)(k2-N,Si-L15)2] (44), related to 2, which reacts with AgTFA
to give the pseudoactahedral complex [Rh(k2-O2CCF3)(k2-N,Si-
L15)2] (45) (Scheme 15).[25] Differently to 40, the rhodium
derivative 45 has shown no activity as CO2hydrosillyation
catalyst under the same reaction conditions. However, 45 is an
effective catalyst for the formation of silylcarbamates from the
reaction of CO2with secondary amines and hydrosilanes.[25]
Complex [Ir(H)(Cl)(k2-N,Si-L17)(coe)] (39) reacts with AgOTf
to afford the triflate derivative [Ir(H)(k1-O-OTf)(k2-N,Si-L17)(coe)]
(46) (Scheme 16). Both species 39 and 46 are active catalysts for
the reduction of formamides to the corresponding methylamine
with hydrosilanes. Moreover, using 39 as catalyst, the reaction
proceeds step by step, making it possible to obtain selectively
the corresponding O-silylatedhemiaminal.[21] The reaction of 39
with PCy3and/or PHtBu2quantitatively affords the species
[Ir(H)(Cl)(k2-N,Si-L17))(L)] (L=PCy3,47; PHtBu2,48), which reacts
with AgOTf to give the corresponding triflate derivative [Ir-
(H)(OTf)(k2-N,Si-L17)(L)] (L=PCy3,49; PHtBu2,50). In presence of
H2O the 16-electron unsaturated iridium triflate derivatives 46,
49 and 50 are in equilibrium with the corresponding water
aduct [Ir(H)(OTf)(k2-N,Si-L17)(L)(OH2)] (L=coe, 51; PCy3,52;
PHtBu2,53) (Scheme 16), which were characterized in solution
by means of NMR spectroscopy and by X-ray diffraction
methods.[26] These results show that the IrSi bond in species
48,49 and 50 is stable in the presence of moisture. Indeed,
hydrolysis was only observed in the presence of an external
base (NEt3). Complexes 46 and 47 have proven to be selective
Scheme 14. Synthesis of the Ir-(k2-N,Si) complexes 40,41,42 and 43.
Scheme 15. Synthesis of the Ir-(k2-N,Si) complexes 44 and 45.
Scheme 16. Reaction sequence from 39,47 and 48 towards the aquo
complexes 51,52 and 53.
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catalysts for the hydrolysis of HSiMe(OSiMe3)2to give the
corresponding hydroxysilane HOSiMe(OSiMe3)2.[26]
Complex 39 reacts with 4,4’-dimethyl-2,2’-bipyridine (bi-
pyMe2) in toluene at 353 K to give the 18-electron saturated
species [Ir(H)(Cl)(k2-N,Si-L17)(bipyMe2)] (54), which reacts with
AgOTf to afford the triflate derivative [Ir(H)(OTf)(k2-N,Si-L17)(bi-
pyMe2)] (55) (Scheme 17).[27] Complex 55 has been found to be
an effective catalyst for the selective solventless dehydrogen-
ation of formic acid,[27] its activity being slightly higher than that
found for 40.[28]
The rhodium species [Rh(H)(Cl)(k2-N,Si-L17)(L)] (L=PCy3,56;
PHtBu2,57) related to the iridium derivatives 47 and 48,
respectively, were prepared by reaction of [{Rh(coe)2}2(μ-Cl)2]
with one equivalent of the proligand L17-H per rhodium in the
presence of stoichiometric amounts of PCy3(or PHtBu2) at 273 K.
Treatment of toluene solutions of 56 (or 57) with one
equivalent of AgOTf affords the corresponding compounds
[Rh(H)(OTf)(k2-N,Si-L17)(L)] (L=PCy3,58; PHtBu2,59)
(Scheme 18).[29]
Complexes 56–59 have proven to be effective catalyst for
the selective hydrogenation of alkenes to alkanes. The best
catalytic performance has been obtained when using the
rhodium-triflate derivative 58 as catalyst at 353 K, which allows
the quantitative and selective formation of the corresponding
alkane in all the studied cases. It should be noted that the
related iridium species 49, although it is also active as alkene
hydrogenation catalysts shows a poorer catalytic
performance.[29]
Reaction of the proligand N-(dimethylsilyl)-N-methylpyridin-
2-amine (L18-H) with [Fe(PMe3)4] has been successfully used to
prepare the iron(II) complex [Fe(H)(k2-N,Si-L18)(PMe3)3] (60),
which by reaction with alkyl halides (MeI or EtBr) affords the
corresponding substitution product [Fe(X)(k2-N,Si-L18)(PMe3)3]
(X=I, 61; Br, 62). The FeH complex 60 reacts with CO2and
phenylisocianate to give the corresponding insertion products
[Fe(k2-O2CH)(k2-N,Si-L18)(PMe3)2] (63) and [Fe(k2-N,O-
PhNCHO)(k2-N,Si-L18)(PMe3)2] (64). The FeH bond of com-
pound 60 reacts with acetylacetone (Hacac) to produce H2and
complex [Fe(acac)(k2-N,Si-L18)(PMe3)2] (65) (Scheme 19).[30]
The addition of the proligand L18-H to the Ru(0) complex
[Ru(η4-C8H12)(η6-C8H10)] has been the entrance door to the
chemistry of ruthenium with the k2-N,Si-L18 ligand. The
reaction of [Ru(η4-C8H12)(η6-C8H10)] with one equivalent of L18-H
gives the ruthenium(II) complex [Ru(k2-N,Si-L18)(η4-C8H12)(η3-
C8H11)] (66), which reacts with excess of L18-H at 333 K to give
the species [Ru(H)(k2-N,Si-L18)3] (67). Complex 67 can be also
obtained by reaction of [Ru(η4-C8H12)(η6-C8H10)] with excess of
Scheme 17. Synthesis of the Ir-(k2-N,Si) complexes 54 and 55.
Scheme 18. Synthesis of the Rh-(k2-N,Si) complexes 56,57,58 and 59.
Scheme 19. Synthesis of the Fe-(k2-N,Si) complexes 60–65.
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L18-H at 333 K. The reaction of 66 with one equivalent of L18-H
under H2(3 bar) atmosphere give the dinuclear complex [{Ru-
(H)(k2-N,Si-L18)2}(μ-H)2] (68), which by reaction with 2.5 equiv-
alents of L18-H at 323 K gives 67 (Scheme 20).[31]
2.2. Transition Metal Complexes with k2-P,Si Ligands
Phosphanosilyl moieties are usually bounded to the metal
center as a bidentate chelate-type ligand. This chelate effect
increases stability of the TM-(k2-P,Si) complexes avoiding the
elimination of silyl groups from the metal center via reductive
elimination, nucleophilic attack at the silicon atom, insertion or
σ-bond metathesis.[32]
To the best of our knowledge, the first examples of TM-
complexes with monoanionic k2-phosphanosilyl ligands
(X2SiCH2CH2P(CH3)2, X=CH3,L19; X=Cl, L20), were reported by
Grobe and Walter in 1977.[33] Thus, the Mn-(k2-P,Si) complexes
[Mn(k2-P,Si-{SiX2CH2CH2P(CH3)2})(CO)4] (X=CH369; Cl, 70) were
successfully synthetized by reaction of Na[Mn(CO5)] and [Mn-
(H)(CO)5] with the corresponding proligand to afford the silyl
complexes [Mn(k1-Si-{SiX2CH2CH2P(CH3)2})(CO)5], which by pho-
tochemical activation of a MnCO bond evolve to the
corresponding complex 69 or 70 (Scheme 21).[33]
It was not until 1981 that a systematic approach to prepare
[Pt(k2-P,Si-SiR1R2CH2CH2PPh2)] (R1=R2=Me, 71 a; R1=R2=Ph,
71 b; R1=Me, R2=Ph, 71 c; R1=H, R2=Me, 71 d; R1=H, R2=Ph,
71 e) species was reported by Stobart et al.[34] This family of Pt-
(k2-P,Si) complexes was easily obtained by oxidative addition of
the SiH bond of the corresponding PPh2CH2CH2SiHR1R2proli-
gand to [Pt(cod)2] (Scheme 22). Since these pioneering results
the chemistry of TM-(k2-P,Si) complexes developed significantly
in subsequent decades. In this regards Okazaki and coworkers
published a review that describes the chemistry of TM-(k2-P,Si)
complexes published until 2002.[6] Therefore, our present
revision focuses attention on results published from 2002
onwards.
Sunada and coworkers reported the reaction of [Pd-
(CNtBu)2]3with the disilane (Ph2PCH2)Ph2Si-SiPh2(CH2PPh2) (L21)2
to form a triangular palladium cluster.[35] Thus, reaction of 4 / 3
equivalents of [Pd(CNtBu)2]3with (L21)2in toluene at 353 K led
to the formation of a trinuclear palladium cluster (72) with two
k2-P,Si chelating ligands linked by a CH2-Ph2Si-CH2
backbone
generated via a skeletal rearrangement of the disilane frame-
work (Scheme 23).
Sunada group also has found that disilanes (L21)2and
(L22)2react with [{Ir(cod)}2(μ-Cl)2] to give the 16-electron
unsaturated complexes [Ir(Cl)(k2-P,Si-SiR2CH2PPh2)2] (R=Ph, 73;
R=Me, 74) (Scheme 24).[36] The IrSi bond distances found in
74 are in expected range for Irsilyl bonds (Table 2). Complexes
73 and 74 are active catalysts for the (E)-selective semi-
hydrogenation of alkynes. The performance of these iridium
species depends on the substituents on the silicon atoms, being
Scheme 20. Synthesis of the Ru-(k2-N,Si) complexes 66,67 and 68.
Scheme 21. Synthesis of [Mn(k2-P,Si-{SiX2CH2CH2P(CH3)2}(CO)4] (X=CH369;
Cl, 70).
Scheme 22. Synthesis of Pt-(k2-P,Si) complexes 71 a-e.
Scheme 23. Synthesis of trinuclear palladium cluster 72.
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74, with methyl substituent more active and selective than
73.[36]
Sola et al. reported the slow transformation of [Ir-
(H)2(biPSiF)(NCMe)2]BF4(biPSiF=k2-P,Si-FSi(Me){(CH2)3PPh2}2)
into the Ir-(k2-P,Si) complex [Ir{k2-P,Si-L23}(k2-C,P-
CH2CH2CH2PPh2)(NCMe)2]BF4(75), (L23 =
SiF(Me)CH2CH2CH2PPh2) (Scheme 25). The IrSi bond distance in
75 (2.3233(18) Å) is in the range of Irsilyl bond distances. The
formation of 75 can be described as a H2loss followed by SiC
bond activation. This assumption is supported by the fact that
reaction times decrease significantly by adding a hydrogen
acceptor as ethylene and demonstrates that the silicon atom at
the polydentate ligand biPSi remains a reactive site.[37]
Le Floch, Sabo-Etienne and collaborators have reported the
reaction of the Ru(II) complex [RuH2(H2)2(PCy3)2] with three
equivalents of the proligand PPh2CH2OSiMe2H (L24-H), which
results in the coordination of three ligands units and the
substitution of the two PCy3and two H2molecules. The product
of this reaction has been characterized by means of 1H, 29Si
NMR and theoretical calculations as an equilibrium between the
ruthenium(IV) species [Ru(H)2(k2-P,Si-L24)2(k1-P-L24-H)] (76 a)
and the ruthenium(II) complex [Ru(H)(k2-P,Si-L24)(k2-P,Si-H,-L24-
H)(k1-P-L24-H)] (76 b) and (Scheme 26).[38]
Ko, Kang and collaborators reported in 2004 the formation
of stable trans-bis(k2-P,Si-chelate)metal complexes, using the
(phosphinoalkyl)silane proligands L25a-H and L25b-H
(Scheme 27) with a two-carbon skeleton connecting the silicon
and phosphorus atoms that is part of a bulky o-carboranyl
unit.[39] Reaction of the coordinatively unsaturated group 10
metal complex [Pt(PPh3)2(C2H4)] with L25a-H and/or L25b-H
gave the corresponding metal complex [Pt{k2-P,Si-Ln}2] (Ln =
L25a,77 a;Ln =L25b,77 b)via chelate-assisted oxidative
addition of the SiH bond at palladium or platinum and
subsequent release of H2(Scheme 27). The trans-complexes,
77 a and 77 b, can be isomerized to the corresponding cis
species 78 a and 78 b, respectively, by thermal treatment
(383 K) of their toluene solutions in the presence of an activated
acetylene such as dimethyl acetylenedicarboxylate (DMAD).[39]
The trans/cis disposition of the ligand in the reaction
product depends on the nature of the metallic precursor. Thus,
when [Pt(cod)2] was used as precursor, instead of [Pt-
(PPh3)2(C2H4)], mixtures of trans/cis isomers in different ratios
were obtained (Scheme 27). The palladium precursor [Pd2(dba)3]
(dba=dibenzylideneacetone) reacts with L25a-H to give a
mixture of complexes 79 a and 80 a in a ratio of 2:1,
Scheme 24. Synthesis of Ir-(k2-P,Si) complexes 73 and 74.
Scheme 25. Synthesis of the Ir-(k2-P,Si) complex 75.
Scheme 26. Synthesis of 76 represented by two arrested structures (76 a and
76 b).
Scheme 27. Reactivity of the phosphinoalkylsilanes L25a-H, L25b-H and
L25c-H with metallic precursors (MLn=[Pt(PPh3)2(C2H4)], [Pt(cod)2] and
[Pd2(dba)3]).
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respectively. However, the reaction of [Pd2(dba)3] with L25b-H
or L25c-H is selective to the formation of the corresponding cis
isomer, 80 b (65%) or 80 c (60%), respectively. These results
indicate that the stereoselectivity of the reaction depends on
the electronic and steric characteristics of the ligands around
the metal center.[39]
Interestingly, the reaction of [Pt(PPh3)2(C2H4)] with L25c-H
results in the mono(chelate) complex [Pt(H)(k2-P,Si-L25c)(PPh3)]
(81), and the formation of the bis(chelate) species 77 c or 78 c
was not observed. In the same way, [Pt(cod)2] reacts with L25c-
H in the presence of the bulky ancillary o-carboranylphosphine
ligand (Cab)PPh2to provide the sterically encumbered complex
[Pt(H)(k2-P,Si-L25c){k1-P-(Cab)PPh2}] (82) (Scheme 28).[39]
The ortho-silylated triphenylphosphine fragment k2(P,Si)-
SiMe2C6H4PPh2(L26) can act as a ligand with a variety of TM. To
the best of our knowledge, the first example of a TM-complex
with this type of ligands was reported by Roper et al. in 1990.
They obseved that the reaction of [Os(H)(Cl)(CO)(PPh3)2] with
Hg(SiMe3)2did not afford the expected product, [Os(SiMe3)Cl-
(CO)(PPh3)2], but the complex [Os(k2-P,Si-L26)(k2-C,P-
C6H4PPh2)(CO)(PPh3)] (83) was obtained in good yield
(Scheme 29).[40] Some years later, a synthetic approach was
published by the same group. Thus, refluxing toluene solutions
of [Os(SiMe3)(Me)(CO)(PPh3)2] in the presence of PPh3results in
the formation of complex 83, which was isolated as colourless
crystalline solid in 50% yield.[41] An analogous compound
[Os(k2-P,Si-L26)(k2-C,P-C6H4PPh2)(CO)(P(C4H4N)3)] (84) was
formed by thermal reaction of [Os(SiMe3)(Me)(CO)(PPh3)2] in the
presence of tris(N-pyrrolyl)phosphine (P(C4H4N)3) instead of
triphenylphosphine (Scheme 29). The OsSi bond distances in
complexes 83 (2.4716(13) Å) and 84 (2.5110(8) Å) are longer
than usual (around 2.45 Å),[41] but they are still in the Ossilyl
bond distance range.[2b,c,d]
The formation of complexes 83 and 84 was postulated to
occur through a dimethylsilylene intermediate arising from a
migration of a methyl group from the trimethylsilyl group to
osmium.[41] This assumption is based on a study previously
reported by Tobita, Ogino and collaborators[42] in which the
same ortho-silylated ligand k2-Si,P-SiMe2C6H4PPh2(L26) is
formed in the thermal reaction of the base-stabilised silylene-
triphenylphosphine ruthenium(II) complex [Ru(η5-C5H5)(Ph3P)-
{SiMe2·O(Me)·SiMe2}] in the presence of different two-electron
donor ligands to give the corresponding species [Ru(η5-
C5H5)(k2-P,Si-L26)L] (L=PPh3,85 a; L=PMe3,85 b; L=PEt3,85 c;
L=P(OMe)3,85 d; L=CNtBu, 85 e) (Scheme 30). The proposed
mechanism implies a CH bond activation of a phenyl group by
the Ru=Si double bond. To the best of our knowledge, this was
the first example of a CH bond activation assisted by a silylene
complex. When a toluene solution of [Ru(η5-C5H5)(Ph3P)-
{SiMe2·O(Me)·SiMe2}] was heated in the absence of a ligand a
ortho-silylated ruthenium(IV) complex [Ru(η5-C5H5)(H)(k2-P,Si-
L26)(SiMe2OMe)] (86) is formed. Complex 86 evolves to 85 a, by
reductive elimination of HSiMe2(MeO), when was heated in the
presence of PPh3, which suggests that 86 is an intermediate for
the formation of complexes 85 a-e(Scheme 30).[42]
In 2017, Sun and coworkers reported the synthesis of cobalt
complexes bearing the k2-(P,Si)-L26 ligand.[43] The reaction of
the proligand o-HSi(Me)2(PPh2)C6H4(L26-H) with [Co(Me)(PMe3)3]
led to formation of the Co(I)-silyl complex [Co(k2-P,Si-
L26)(PMe3)3] (87). On the other hand, the reaction of L26-H with
Scheme 28. Synthesis of the Ir-(k2-P,Si) complexes 81 and 82.
Scheme 29. Synthesis of the Os-(k2-P,Si) complexes 83 and 84.
Scheme 30. Synthesis of the Ru-(k2-P,Si) complexes 85 a-eand 86.
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[Co(Cl)(PMe3)3] gave the Co(III) species [Co(H)(Cl)(k2-P,Si-
L26)(PMe3)2] (88). They also proved that the Co(III) complex 88
can be reduced with a strong base such as MeLi to give 87 in
the presence of PPh3(Scheme 31).[43] The silyl [P,Si]-chelate
cobalt hydride 88 is catalytically more active for Kumada
coupling reactions of aryl chlorides or aryl bromides with
Grignard reagents than the related tridentate Co-(k3-P2,Si)[44] and
tetradentate Co-(k4-P3,Si)[45] cobalt hydride derivatives.
Same authors reported reaction of 87 with one equivalent
MeI or EtBr to afford the corresponding Co(II) complex [Co-
(X)(k2-P,Si-L26)(PMe3)2] (X=I, 89; Br, 90). The CoSi bond
distances in 87 (Co(I); 2.3353(5) Å) and 89 (Co(II); 2.3368(9) Å)
are longer than the CoSi bond distance in the Co(III) complex
88 (2.2735(10) Å),[43] all of them in the Cosilyl range
(Scheme 31).[2b,c,d]
Few years after, same group synthetized the iron silyl
hydride complex [Fe(H)(k2-P,Si-L26)(PMe3)3] (91) by reaction of
L26-H with Fe(PMe3)4.[46] The proposed mechanism for the
formation of 91 involves the displacement of one PMe3ligand
to give the intermediate [Fe(k1-P-L26-H)(PMe3)3] (91-I), followed
by coordination of the SiH bond to the metal center
accompanied by the dissociation of other PMe3ligand to afford
[Fe(k2-P,SiH-L26-H)(PMe3)2] (91-II). Finally, the electron-rich
iron(0) center activates the SiH bond via oxidative addition to
form 91 upon coordination of one molecule of PMe3
(Scheme 32). The iron(II) species 91 showed high catalytic
activity for the reduction of aldehydes and ketones with
hydrosilanes, as well as, for the reduction of benzamide to
cyanobenzene with HSi(OEt)3. Furthermore, catalyst 91 is able
to selectively catalyse the reduction of α,β-unsaturated carbon-
yls to the corresponding α,β-unsaturated alcohols.[46]
More recently, Huertos and coworkers reported the syn-
thesis of rhodium and iridium complexes with the (k2-P,Si-L26)
ligand.[47] The reaction of dimers [{M(coe)2}2(μ-Cl)2] (M =Rh, Ir)
with 4 equivalents of the proligand L26-H led to the formation
of the corresponding complex [M(Cl)(k2-P,Si-L26)2] (M=Rh, 92;
Ir, 93). When the Rh derivative 92 was treated with NaBArF4in
CH2Cl2followed by addition of a small amount of CH3CN, the
cationic rhodium derivative [Rh(k2-P,Si-L26)2(NCCH3)][BArF4] (94)
was formed. A related iridium cationic compound [Ir(k2-P,Si-
L26)2(NC CH3)2][BArF4] (95) bearing two coordinated CH3CN
molecules was obtained when the reaction of 93 and NaBArF4
was performed under the same reaction conditions
(Scheme 33). The metalSi bond distances in complexes 92,93,
94 and 95 are in the range expected for metalsilyl bonds
(Table 2). These four complexes (92,93,94 and 95) are active
Scheme 31. Synthesis of the Co-(k2-P,Si) complexes 87,88, 89 and 90.
Scheme 32. Proposed mechanism for the formation of 91.
Scheme 33. Synthesis of complexes 92,93,94 and 95.
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catalysts in the hydrolysis of dihydrosilanes to give the
corresponding silanol, silanediol or hidrosiloxane products
selectively, depending on the catalyst/substrate combination.
The authors postulate that the electronic nature of both catalyst
and substrate controls the selectivity of the hydrolytic proc-
esses, while steric factors influence condensation events.[47]
Smith and coworkers reported the proligand o-HSi(iPr)2(P(p-
Tolyl)2)C6H4(L27-H), related to L26-H but with isopropyl and p-
tolyl substituents at the silicon and phosphorous atoms,
respectively.[48] The proligand L27-H was designed to create an
electron-rich framework that could facilitate CH cleavage. The
reaction of L27-H with [{Ir(cod)}2(μ-OMe)2] gives the complex
[Ir(k2-P,Si-L27)(cod)] (96) (Scheme 34). The structure of the Ir(I)
complex 96 is square-planar with the IrSi bond distance of
2.376(2) Å, typical for a Irsilyl bond. Complex 96 has been
found to be active as homogeneous catalyst for the borylation
of a broad range of substituted aromatic compounds.[48]
The k2(Si,P)-SiMe2PCy2C6H4(L28) ligand, related to L26 but
with cyclohexyl substituents at the phosphorus atom instead of
phenyl groups, was generated in situ due to an unusual ligand
rearrangement of [M(k3-P,Si,P)(Me)] (M=Ni, Pd) species that
involves SiC(sp3) bond formation to generate a M(0) inter-
mediate followed by a SiC(sp2) oxidative addition to the metal
centre to afford the corresponding complex [M(k2-P,Si-L28)(k2-
P,C-o-C6H4PCy2)] (M=Pd, 97; Ni, 98). In the case of nickel
complex 98, these SiC bond activation processes are rever-
sible. Palladium complex 97 could be also obtained by direct
reaction of (2-Cy2PC6H4)2SiMe2with 0.5 equivalents of
[Pd2(dba)3] (Scheme 35).[49]
Same group published the first P,Si,Nmixed-donor silyl
pincer ligand (L29) derived from the precursor
SiHMe(2-tBu2PC6H4)(2-Me2NC6H4) (L29-H).[50] The authors found
that the amino donor of this molecule is labile and the
hemilability of the P,Si,Nligand promotes the isolation of the
Pd- and Pt-(k2-P,Si) complexes [M(X)(k2-P,Si-L29)(PMe3)] (M=Pd,
X=Br; 99; M=Pt, X=Cl; 100). These group 10 complexes were
synthetized by reaction of PdBr2or PtCl2(cod) with L29-H in the
presence of NEt3to give the corresponding square planar
complexes [M(X)(k3-P,Si,N-L29)]. The addition of PMe3produces
the selective displacement of the amine arm from the metal
center to give 99 or 100, respectively (Scheme 36). A related
rhodium complex was obtained following similar reaction
sequence. Thus, [Rh(H)(Cl)(k3-P,Si,N-L29)] was obtained from
reaction of the dimer [{Rh(cod)}2(μ-Cl)2] with L29-H. Then,
addition of PMe3led to the quantitative formation of [Rh-
(H)(Cl)(k3-P,Si-L29)(PMe3)] (101) (Scheme 36).[50]
Recently, He et al. have published an efficient one-pot
method for the synthesis of P-atropisomeric Si-stereogenic
monohydrosilanes with excellent stereoselectivity.[51] To prove
the potential of the new chiral phosphine Si-stereogenic
monohydrosilane as ligands, reactions with different metal
fragments were tested. Treatment of [{M(cod)}2(μ-Cl)2] (M =Rh
or Ir) with 4 equivalents of two different phosphine-based
monohydrosilanes L30-H and L31-H in toluene at room temper-
ature gave the chiral metal-silicon air-stable complexes 102 (Rh)
and 103 (Ir) respectively (Scheme 37).
2.3. Transition Metal Complexes with k2-S,Si and k2-O,Si
Ligands
The first examples of TM-(k2-S,Si) complexes were reported in
2015 by Huertos et al. They prepared the rhodium(III) dinuclear
complex [Rh(k2-S,Si-L32)2}2(μ-Cl)2] (104) by reaction of four
equivalents of the proligand SiMe2H(o-C6H4SMe) (L32-H) with
[{Rh(cod)}2(μ-Cl)2] in CH2Cl2(Scheme 38).[52] The formation of 104
takes place via the Rh(I)/Rh(III) mixed-valent species [{Rh(k2-S,Si-
L32)}{Rh(cod)}(μ-Cl)2] (105), which could be isolated from the
reaction of [{Rh(cod)}2(μ-Cl)2] with two equivalents of L32-H.[52]
Scheme 34. Synthesis of the Ir-(k2-P,Si) complex 96.
Scheme 35. Synthesis of complexes 97 and 98.
Scheme 36. Synthesis of complexes 99,100 and 101.
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The RhSi bond distances in 104, 2.3154(11) Å and 2.3104(10)
Å, and in 105, 2.2992(9) Å and 2.3030(9) (10) Å, clearly show the
silyl character of these bonds (Table 3).[2b,c,d]
In subsequent studies, Huertos et al. prepared the cationic
complex [Rh(H)(k2-S,Si-L32)(PPh3)2][BArF4] (106) by reaction of
the proligand L32-H with [Rh(Cl)(PPh3)3] and NaBArF4in CH2Cl2
at r.t. (Scheme 39).[53] Complex 106 has shown to be an effective
catalyst precursor for the solvent-free tandem isomerization-
hydrosilylation of internal olefins, showing complete selectivity
to the formation of silanes with linear alkyl chains.[53] Moreover,
106 also catalyzed the reduction of alkyl halides with
triethylsilane. These reactions are performed in a solvent-free
manner. Few years later, Huertos et al. prepared the family of
proligands [SiMe2H(o-C6H4SR)] (R=iBu, L33-H; pentyl, L34-H;
benzyl, L35-H; neopentyl, L36-H), related to L32-H but with
different substituents on the sulfur atom.[54] The reaction of the
proligand (L33-H, L34-H, L35-H or L36-H) with [Rh(Cl)(PPh3)3]
and NaBArF4in CH2Cl2affords the corresponding cationic
species [Rh(H)(k2-S,Si-Ln)(PPh3)2][BArF4] (Ln =L33,107;L34,108;
L35,109;L36,110) (Scheme 39).[54] These new cationic Rh(III)
compounds, (106-110) have proved to be efficient catalysts for
the solvent-free tandem isomerization-hydrosilylation reaction
of alkenes forming the anti-Markovnikov terminal silyl alkanes
as the only silylated products.[54]
Ghosh et al. have recently reported the in situ preparation of
the ligands {k2-S,Si-(NSiPhR)(S2C7H4)} (R=H, L37; Ph, L38) by the
thermal reaction of the ruthenium borate species [Ru(k2-N,S-
C7H4NS2){k3-H,S,S’-H2B(C7H4NS2)2}PPh3] with PhRSiH2(R=H, Ph).
The reaction with one equivalent of PhRSiH2in toluene at 333 K
led to a mixture of complexes including [Ru{k2-S,Si-(Ln)}{k3-
H,S,S’-H2B(C7H4NS2)2}(PPh3)] (Ln =L37,111 a/b;L38, 112 a/b) and
the hydridotrisilyl complex [Ru(H)(k2-S,Si-(L38)3] (113)
(Scheme 40). However, the reaction with excess (3 equiv) of
Scheme 37. Synthesis of complexes 102 and 103.
Scheme 38. Synthesis of the complexes 104 and 105.
Scheme 39. Synthesis of the Rh-(k2-S,Si) complexes 106–110.Scheme 40. Reactivity of [Ru(k2-N,S-C7H4NS2){k3-H,S,S’-H2B(C7H4NS2)2}PPh3]
with PhRSiH2(R=H, Ph).
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Ph2SiH2at 363 K selectively affords [Ru(H){k2-S,Si-(L38}3] (113),
which was also selectively obtained by addition of excess of
Ph2SiH2to a mixture of complexes 112 a/b.[55]
Examples of TM-complexes with k2-(O,Si) ligands are also
known. Roper, Wright and collaborators reported the reaction
of [Ru(SiClPh2)(k2-S2CNMe2)(CO)(PPh3)2] with thallium acetate to
afford the ruthenium complex [Ru(k2-O,Si-Si(OC(O)Me)Ph2)(k2-
S2CNMe2)(CO)(PPh3)] (114) by nucleophilic substitution at the
SiCl by acetate favored by the precipitation of TlCl
(Scheme 41).[18]
Recently, Hass et al. reported a stable Ti(III) species,
[TiCp2{k2-O,Si-(Si{Si(OMe)3}2-Si(OMe)2-OMe)] (115), when at-
tempted disilylation of titanocenedichloride with 2 equivalents
of potassium tris(trimethoxysilyl)silanide [(MeO)3Si]3SiK
(Scheme 42).[56] This radical is stabilized by donation of a lone
pair of one oxygen atom of a methoxy group giving rise to k2-
(O,Si) coordination mode. The TiSi bond length (2.7432(7) Å) is
significantly increased compared to related chloro-Ti(IV) com-
plex [TiCp2Cl{Si(Si(MeO)3)3}] (2.7037(7) Å) (Table 4).
2.4. Transition Metal Complexes with k2-C,Si Ligands
Silyl and N-heterocyclic carbene (NHCs) ligands are strongly σ-
donating ligands with a strong trans-effect. Examples of TM-
complexes with functionalized NHC ligands featuring silyl
donors groups have remained difficult to catch, although some
NHCs with silyl substituents on the imidazole ring are known.
Deng et al. reported in 2013 that the reaction of the cyclo-
metallated iron(II) complex [Fe(IMes’)2Fe] (IMes’=cyclometa-
lated IMes ligand, IMes=1,3-dimesitylimidazol-2-ylidene) with
PhMeSiH2or Ph2SiH2at r.t. leads to the corresponidng silylated
product [Fe(k2-C,Si-SiPhR-IMes’)(IMes’)] (R=Me, 116; Ph, 117)
(Scheme 43).[57]
Deng et al. showed that this methodology can also be
applied to cobalt. They found that [Co(IMes’)2] reacts slowly
with PhSiH3in benzene at r.t. to give the complex [Co(k2-C,Si-
SiPhH-IMes’)(IMes’)] (118). Analogously, the reactions of [Co-
(IMes’)2] with PhMeSiH2and Ph2SiH2in benzene proceeded very
slowly at r.t. to afford the corresponding complex [Co(k2-C,Si-
SiPhH-IMes’)(IMes’)] (R=Me, 119; Ph, 120). It should be
mentioned that when the reaction mixtures were heated to
343 K the formation of complexes 119 and 120 was achieved in
4 hours (Scheme 44).[58]
Through some experiments on the reactivity of 118, they
found that in the presence of H2complex 118 is in equilibrium
with the CoH species [Co(H)(k2-C,Si-SiPhH-IMes’)(IMes)] (121).
The reaction of 118 with BH3-thf leads to the species [Co(H)(k2-
C,Si-SiPhH-IMes’)(k3-C,H2B-BH3-IMes’)] (122) (Scheme 45).[58] Pre-
liminary studies showed that complex 118 catalyzed the hydro-
silylation of 1-octene with PhSiH3with high activity and
selectivity.[58] Deng et al. reported the synthesis of Co complexes
with polydentate NHC-silyl ligands by reaction of 122 with 2-
pyridone.[59] Moreover, the reaction of 122 with [FeCp2][BPh4]
affords Co complexes with tridentate NHCSi-NHC ligands.[60]
Conejero et al. reported that the cationic platinum cyclo-
metallated N-heterocyclic carbene complex [Pt-
(ItBuiPr’)(ItBuiPr)][BArF4] (ItBuiPr’=cyclometalated ItBuiPr ligand,
ItBuiPr=1-tert-butyl-3-isopropylimidazol-2-ylidene) reacts with
primary silanes RSiH3(R=Ph, nBu) leading to the cyclometal-
lated platinum(II) silyl-NHC complexes [Pt{k2-C,Si-(SiHRCH2CMe2-
NHC-iPr)}(ItBuiPr)][BArF4] (R=Ph, 123; R=nBu, 124)
(Scheme 46).[61]
Similarly, the platinum(II) complexes [Pt(IMes’)(IMes)][BArF],
and [Pt(IMes*’)(IMes*)][BArF], (IMes*=1,3- dimesityl-4,5-dimethy-
limidazol-2-ylidene) react very fast with primary silanes RSiH3at
Scheme 41. Synthesis of the Ru-(k2-O,Si) complex 114.
Scheme 42. Synthesis of the Ti-(k2-O,Si) complex 115.
Scheme 43. Synthesis of the complexes [Fe(k2-C,Si-SiPhR-IMes’)(IMes’)] (R =
Me, 116; Ph, 117).
Scheme 44. Synthesis of the complexes [Co(k2-C,Si-SiPhH-IMes’)(IMes’)]
(R=H, 118; Me, 119; Ph, 120).
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r.t. to generate the corresponding silyl-cyclometallated com-
plexes 125,126,127 and 128 (Scheme 47).[61]
2.5. Transition Metal Complexes with k2-E,Si (E =Si, Ge, Sn)
Ligands
Unsaturated tetryl species (silyl, germyl or stannyl) are inher-
ently stronger σ-donors than the corresponding carbon species,
while enhancing π-accepting character on going down in the
group. In 2020, Scheschkewitz’s group reported first TM-(k2-E,Si)
complexes.[62] Reaction of siliconoids functionalized with a
tetrylene side-arm (E=Si, L37; Ge, L38; Sn, L39) towards
[{Ir(coe)2}2(μ-Cl)2] afforded the corresponding k2-E,Si tetrylene-Si6
iridium complexes (E=Si, 129; Ge, 130; Sn, 131) (Scheme 48).
Authors propose a mechanism for the formation of these
complexes starting with coordination of the pendant tetrylene
atom of the ligand to the metal and subsequnent oxidative
addition of a SiE single bond. Then, reductive elimination of
the chlorine atom and Si(Tip)2(Tip=2,4,6-tris(isopropyl)phenyl)
fragment gives the final products with a exohedral chlorosilyl
group. The IrSi(silyl) bond lengths 2.320(1) Å for 129 and
2.3517(7) Å for 130 and IrE 2.334(1) Å (E=Si, 129) and
2.4113(3) Å (E=Ge, 130) are those of single bonds (Table 6). All
complexes have proven to be active catalysts for isomerization
of terminal alkenes to 2-alkenes.
Recently, Maron, Jones and coworkers published the syn-
thesis of first silicon analogue of an abnormal N-heterocyclic
carbene.[63] Insertion of CO into the SiN bond of the aminidate-
stabilized 1,2-disilylene [{ArC(NDip)2}Si]2(Dip=2,6-diisopropyl-
phenyl, Ar=4-C6H4tBu), and SiSi bond cleavage affords dis-
ilylene L40. Mo(CO)6reacts with L40 under UV light at r.t. to
give the chelated bis(silylene) molybdenum complex 132
(Scheme 49). This complex can also be obtained from reaction
Scheme 45. Reactivity of 118 with H2and BH3-thf.
Scheme 46. Synthesis of the Pt(II) NHC-silyl complexes 123 and 124.
Scheme 47. Synthesis of the Pt(II) NHC-silyl complexes 125,126,127 and
128.
Scheme 48. Synthesis of complexes 129,130 and 131.
Scheme 49. Synthesis of the Mo-(k2-Si,Si) complex 132.
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of [{ArC(NDip)2}Si]2with Mo(CO)6under irradiation conditions
suggesting that CO dissociated from Mo(CO)6reacts with the
disilylene to give L40, which reacts with molybdenum carbonyl
species affording 132. Complex 132 was characterized by X-ray
diffraction analysis and molecular structure shows silicon
centers chelating a Mo(CO)4fragment in a cis-fashion to give a
five-membered ring. The reported MoSi bond distances
2.478(2) and 2.5186(15) Å (Table 6) are in the known range for
neutral silylene molybdenum carbonyl complexes (2.447–
2.578 Å).[63]
3. Analysis of metalSi distances in TM-(k2-L,Si)
complexes
Tables 1 to 6 show the metalSi bond distances reported for
the complexes included in this review. All of them fall within
the usual range of distances for metalsilyl bonds.[2b,c,d,65]
Stablishing a general trend of behavior is difficult because not
many examples of this type of complexes have been published
to date. However, in the case of rhodium and iridium complexes
with k2-N,Si and k2-P,Si ligands there are enough examples to
illustrate that, regardless of the silicon substituents and the
nature of linker, the metalSi bond distances in Rh- and Ir-(k2-
N,Si) species are shorter than in related Rh- and Ir-(k2-P,Si)
complexes. This behavior could be due to a greater σ-donor
character of the phosphine moiety in k2-P,Si ligands compared
to the nitrogen of the corresponding k2-N,Si ligand.
TM-complexes with monoanionic k2-pyridine-2-yloxy-silyl
based exhibit short metalSi bond distances, between 2.23-
2.29 Å (for Rh) and 2.25-2.29 Å (for Ir) (Table 1). This was the
reason for some authors to propose them as examples of base-
stabilized metalsilylene bonds.[16,17,18] In this regards, our group
published in 2020 a QTAIM analysis of the IrSi bond in 2-
pyridone-stabilized silyl iridium complexes, which allowed to
conclude that the IrSi bonds in these complexes can be
considered as an intermediate between the base-stabilized
silylene and silyl cases.[20] Theoretical calculations based on
Energy Decomposition Analysis (EDA) in combination with the
Natural Orbital for Chemical Valence (NOCV) were performed
for Ir-(k3-N,Si,N),[64] Ir-(k2-N,Si)[26] and Rh-(k2-N,Si)[29] complexes.
The obtained results showed the covalent nature of the
metalSi bond and the significant role of electrostatic inter-
actions on it. Indeed, the electrostatic component of the bond
has been found to be almost twice as strong as the total orbital
interactions. This fact indicates a highly polarized covalent
bond, which can explain the shortening of MSi (M=Rh, Ir)
bond distances in these type of complexes.
Therefore, in all the examples collected in this review the
metal-silicon bond distance falls within the range of distances
that would be expected for metalsilyl bonds.[2b,c,d,65] Although
in some cases, metalSi bond distances shorter than expected
have been observed. The bond shortening is mainly due to the
ionic component contribution since the backbonding from d
orbitals of the metal to the σ* orbitals of the silicon is
considerably low.[26,29,64]
Table 1. Selection of metalSi bond distances reported for TM-(k2-N,Si)n(n=1, 2, 3) complexes.
MSi Complex Bond-distance (Å) Number of
k2-L,Si ligands
Ref.
CoSi 13[a] 2.2375(9) (A)
2.2311(8) (A)
2.2392(9) (A)
2.2315(8) (B)
2.2424(9) (B)
2.2404(9) (B)
3 [11]
RhSi 22.2571(6)
2.2500(6)
2 [12]
RhSi 52.278(1)
2.290(1)
2.301(1)
3 [10b]
RhSi 16 2.2746(7)
2.2654(8)
2 [12]
RhSi 17 2.2573(8)
2.2498(8)
2 [12]
RhSi 19 2.2635(7) 1 [13]
RhSi 22 2.2985(7) 1 [13]
RhSi 24 2.2648(4) 1 [15a]
RhSi 25 2.2990(8) 1 [15a]
RhSi 45 2.2277(8)
2.2388(10)
2 [25]
RhSi 56 2.2907(6) 1 [29]
RhSi 57 2.2738(3) 1 [29]
RhSi 58 2.2689(3) 1 [29]
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Table 1. continued
MSi Complex Bond-distance (Å) Number of
k2-L,Si ligands
Ref.
IrSi 62.296(4)
2.301(4)
2.305(4)
3 [10b]
IrSi 26 2.3016(10) 1 [15b]
IrSi 27 2.2887(14) 1 [15b]
IrSi 37 2.2634(14)
2.2695(14)
2.2552(14)
2.2747(14)
2 [19]
IrSi 38[a] 2.2515(7) (A)
2.2579(7) (A)
2.2499(7) (B)
2.2700(7) (B)
2 [20]
IrSi 39 2.2853(6) 1 [21]
IrSi 40 2.2645(10)
2.2505(11)
2 [19]
IrSi 41 2.2702(10)
2.2668(11)
2 [20]
IrSi 42 2.2570(5)
2.2615(5)
2 [22]
IrSi 43 2.2573(8)
2.2498(8)
2 [20]
IrSi 47 2.2792(3) 1 [26]
IrSi 48 2.2814(4) 1 [26]
IrSi 49 2.2835(5) 1 [26]
IrSi 51 2.2915(6) 1 [26]
IrSi 53 2.2876(4) 1 [26]
IrSi 55 2.2731(12) 1 [27a]
FeSi 32 2.2640(10) 1 [16b]
FeSi 60 2.246(1) 1 [30]
FeSi 62 2.2455(7) 1 [30]
FeSi 63 2.2166(5) 1 [30]
FeSi 64 2.2248(6) 1 [30]
FeSi 65 2.2338(5) 1 [30]
RuSi 35 2.3487(4) 1 [18]
RuSi 36 2.3400(7) 1 [18]
RuSi 66 2.3809(7) 1 [31]
RuSi 67 2.3213(5)
2.3264(5)
3 [31]
RuSi 68 2.3283(5) 2 [31]
WSi 34 2.5072(10) 1 [17]
[a] The unit cell contains two independent molecules (A and B).
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Table 2. Selection of metalSi bond distances reported for TM-(k2-P,Si)n(n=1, 2) complexes.
MSi Complex Bond-distance
(Å)
Number of
k2-L,Si ligands
Ref.
CoSi 87 2.3353(5) 1 [43]
CoSi 88 2.2735(10) 1 [43]
CoSi 89 2.3368(9) 1 [43]
RhSi 92 2.3099(6) 2 [47]
RhSi 94 2.341(1)
2.311(1)
2 [47]
RhSi 102 2.300(1)
2.300(2)
2 [51]
IrSi 74 2.3337(8)
2.3451(9)
2 [36]
IrSi 75 2.3233(18) 2 [38]
IrSi 93 2.319(5)
2.325(5)
2 [47]
IrSi 95 2.356(1)
2.366(1)
2 [47]
IrSi 96 2.376(2) 1 [48]
IrSi 103 2.338(4)
2.310(4)
2 [51]
RuSi 76 b 2.4240(11)
2.4647(11)
2 [38]
RuSi 85 b 2.352(3) 1 [42]
OsSi 83 2.4716(13) 1 [41]
OsSi 84 2.5110(8) 1 [41]
PdSi 72 2.3331(7)
2.3326(6)
1 [36]
PdSi 80 c 2.361(2)
2.358(2)
2 [39]
PdSi 97 2.3037(4) 1 [50]
PtSi 71 b 2.368(6)
2.342(8)
2 [34]
PtSi 77 a 2.408(1) 2 [39]
PtSi 78 a 2.3492(2)
2.3532(2)
2 [39]
PtSi 78 c 2.361(2)
2.361(1)
2 [39]
PtSi 81 2.307(2) 1 [39]
PtSi 82 2.3228(2) 1 [39]
PtSi 100 2.3077(9) 1 [50]
Table 3. Selection of metalSi bond distances reported for TM-(k2-S,Si)n(n=1, 2, 3) complexes.
MSi Complex Bond-distance (Å) Number of
k2-L,Si ligands
Ref.
RhSi 104 2.3154(11)
2.3104(10)
2 [52]
RhSi 105 2.2992(9)
2.3030(8)
2 [52]
RuSi 111 a 2.300(4) 1 [55]
RuSi 113 2.211(4)
2.364(4)
2.452(4)
3 [55]
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4. Summary and Outlook
This review shows that the chemistry of TM-complexes with
monoanionic bidentate silyl (k2-L,Si) ligands has experienced
great development during the last decade. Among the proper-
ties of this type of ligands are their easy tunable σ-donor
character, and the high trans-effect and -influence of the silyl
group which facilitate the generation of electronically and
coordinatively unsaturated species. There is still much room for
improvement in this field, especially with respect to the
chemistry of complexes with earth-abundant metals. In fact,
most of the so far reported TM-(k2-L,Si) species are complexes
of Rh, Ir, Ru and Pt. Exceptionally, the chemistry of TM-
complexes with k2-C,Si-(silyl-NHC) ligands is dominated by Co,
Fe and Pt complexes.
The most used synthetic methods for the preparation of
TM-(k2-L,Si) complexes include: (i) oxidative addition of the SiH
bond of the proligand assisted by the coordination of the L
donor group; (ii) nucleophilic substitution of one of the silicon
substituents in TMsilyl complexes and (iii) reaction of cyclo-
metalated TM-(k2-C,C-NHC) complexes with primary and / or
secondary silanes. Among them, the assisted oxidative addition
of the SiH of the corresponding proligand stands out.
The metalsilyl bond distances in TM-(k2-L,Si) complexes are
in the expected range for metalsilyl bonding, therefore, they
can be considered as X-type silyl ligands. Conversely, in the
case of TM-(k2-N,Si) complexes is frequent to find metalSi
bond distances shorter than it should be expected for a
metalsilyl bond. Theoretical studies showed the electron-
sharing nature of the covalent metalSi bond, and that the
shortening of the metalSi bond can be explained on the basic
of the significant role of electrostatic attractions between the
TM fragment and the ligand.
The mechanisms of the catalytic processes promoted by
TM-(k2-L,Si) complexes are influenced by the nature of the
ligand. Thus, while using TM-(k2-N,Si) catalysts σ-bond meta-
thesis mechanisms and σ-complex assisted metathesis (CAM)
mechanisms are favored, TM-(k2-P,Si)-catalyzed processes that
follows oxidative addition/reductive elimination mechanisms
are also possible. While the hemilabile character of k2-(N,Si)-
type ligands has not been published, examples of this character
are known in TM-(k2-P,Si) complexes.
Regarding the applications of this type of TM-compounds, it
is worth mentioning that many of these complexes have proven
to be effective catalysts in catalytic hydrosilylation processes of
alkenes, amides, and CO2, selective hydrogenation processes of
olefins and silane hydrolysis processes. Interestingly, some TM-
(k2-L,Si) species have found to be most active than their TM-(k3-
L,Si,L) counterparts in CO2hydrosilylation processes (k2-N,Si vs
k3-N,Si,N) and Kumada coupling processes (k2-P,Si vs k3-P,Si,P).
Although, the application of these systems in asymmetric
catalytic processes has not been widely explored, recent
publications in this regard suggest that the design of TM-(k2-
L,Si) chiral ligands to enhance enantioselectivities will be one of
the lines of development of the chemistry of this type of
complexes.
In conclusion, the chemistry of TM-(k2-L,Si) is still in a
growth stage and it is expected that in the coming years the
number of successful catalytic processes based on TM-(k2-L,Si)
homogeneous catalysts will expand.
Acknowledgements
Financial support from projects PID2021-126212OBI00 (AEI-
Spain) and DGA/FSE project E42_23R (Gobierno de Aragón) is
gratefully acknowledged. M. B. thanks to Campus Iberus and
European Union’s Horizon 2020 research and innovation
program under the Marie Skłodowska program – Grant Agree-
ment No. 101034288. A. G.-E. thankfully acknowledges Universi-
dad de Zaragoza and Banco Santander for a predoctoral
fellowship “Ayudas para iberoamericanos y ecuatoguineanos en
Estudios de Doctorado. Universidad de Zaragoza – Santander
Universidades (2022–2023)”.
Table 4. Selection of metalSi bond distances reported for TM-(k2-O,Si)
complexes.
MSi Complex Bond-distance
(Å)
Number of k2-L,Si li-
gands
ref
RuSi 114 2.3499(13) 1 [18]
TiSi 115 2.7432(7) 1 [56]
Table 5. Selection of metalSi bond distances reported for TM-(k2-C,Si)
complexes.
MSi Complex Bond-distance
(Å)
Number of k2-L,Si li-
gands
ref
CoSi 118 2.300(2) 1 [58a]
CoSi 119 2.309(1) 1 [58a]
CoSi 120 2.327(1) 1 [58a]
CoSi 122 2.274(1) 1 [58a]
FeSi 116 2.396(1) 1 [57]
FeSi 117 2.419(1) 1 [57]
PtSi 123 2.2693(1) 1 [61]
PtSi 125 2.2609(8) 1 [61]
PtSi 126 2.2619(6) 1 [61]
Table 6. Selection of metalSi bond distances reported for TM-(k2-E,Si)
(E=Si, Ge) complexes.
MSi Complex Bond-distance (Å) E ref
IrSi 129 2.320(1)
2.334(1)
Si [62]
IrSi 130 2.3517(7) Ge [62]
MoSi 132 2.478(2)
2.5186(15)
Si [63]
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Conflict of Interests
The authors declare no conflict of interest.
Keywords: silyl complexes ·monoanionic bidentate silyl
ligands ·polydentate silyl ligands ·transition metal complexes
[1] R. J. Lundgren, M. Stradiotto, Key Concepts in Ligand Design. In Ligand
Design in Metal Chemistry (Eds M. Stradiotto and R. J. Lundgren). Wiley,
Weinheim, 2016.
[2] a) J. Gao, Y. Ge, C. He, Chem. Soc. Rev. 2024,53, 4648–4673; b) J. Y.
Corey, Chem. Rev. 2016,116, 11291–11435; c) J. Y. Corey, Chem. Rev.
2011,111, 863–1071; d) J. Y. Corey, J. Braddock-Wilking, Chem. Rev.
1999,99, 175–292.
[3] M. T. Whited, B. L. H. Taylor, Comments Inorg. Chem. 2020,40, 217–276.
[4] Selected reviews: a) J. A. Cabeza, P. García-Álvarez, Chem. Eur. J. 2023,
29, e202203096; b) T. Komuro, Y. Nakajima, J. Takaya, H. Hashimoto,
Coord. Chem. Rev. 2022,473, 214837; c) M. T. Whited, Dalton Trans.
2021,50, 16443–16450; d) M. Simon, F. Breher, Dalton Trans. 2017,46,
7976–7997; e) M. T. Whited, J. Zhang, S. Ma, B. D. Nguyen, D. E. Janzen,
Dalton Trans. 2017,46, 14757–14761; f) M. S. Balakrishna, P. Chandrase-
karan, P. P. George, Coord. Chem. Rev. 2003,241, 87–117.
[5] a) M. Tanabe, K. Osakada, Transition Metal Complexes of Silicon
(Excluding Silylene Complexes), Chapter 2, in Organosilicon Compounds,
Theory and Experiment (Synthesis) (Ed.: V. Y. Lee), Academic Press,
London, 2017; b) E. Sola, Silicon-based pincers: trans influence and
functionality. Chapter 19, in Pincer Compounds: Chemistry and Applica-
tions, (Ed.: D. Morales-Morales) Elsevier, Amsterdam, 2018; c) L. Turculet,
PSiP transition-metal pincer complexes: synthesis, bond activation, and
catalysis, Chapter 6, in Pincer and Pincer-Type Complexes: Applications in
Organic Synthesis and Catalysis, First Edition, (Eds.: K. J. Szabó, O. F.
Wendt), Willey, Weinheim, 2014.
[6] For a review on TM-k2-P,Si complexes see: M. Okazaki, S. Ohshitanai, M.
Iwata, H. Tobita, H. Ogino, Coord. Chem. Rev. 2002,226, 167–178.
[7] a) J. Wagler, R. Gericke, Polyhedron 2023,245, 116663; b) L. Ehrlich, R.
Gericke, E. Brendler, J. Wagler, Inorganics 2018,6, 119; doi: 10.3390/
inorganics6040119.
[8] F. J. Fernández-Alvarez, R. Lalrempuia, L. A. Oro, Coord. Chem. Rev. 2017,
350, 49–60.
[9] H. G. Ang, W. L. Kwik, J. Organomet. Chem. 1989,361, 27–30.
[10] a) P. I. Djurovich, A. Safir, N. Keder, R. J. Watts, Coord. Chem. Rev. 1991,
111, 201–214; b) P. I. Djurovich, A. L. Safir, N. L. Keder, R. J. Watts, Inorg.
Chem. 1992,31, 3195–3196; c) P. I. Djurovich, R. J. Watts, Inorg. Chem.
1993,32, 4681–4682; d) P. I. Djurovich, R. J. Watts, J. Phys. Chem. 1994,
98, 396–397; e) P. I. Djurovich, W. Cook, R. Joshi, R. J. Watts, J. Phys.
Chem. 1994,98, 398–400.
[11] R. Imayoshi, H. Tanaka, Y. Matsuo, M. Yuki, K. Nakajima, K. Yoshizawa, Y.
Nishibayashi, Chem. Eur. J. 2015,21, 8905–8909.
[12] U. Prieto-Pascual, I. V. Alli, I. Bustos, I. J. Vitorica-Yrezabal, J. M. Matxain,
Z. Freixa, M. A. Huertos, Organometallics 2023,42, 2991–2998.
[13] U. Prieto-Pascual, A. Martínez de Morentin, D. Choquesillo-Lazarte, A.
Rodríguez-Diéguez, Z. Freixa, M. A. Huertos, Dalton Trans. 2023,52,
9090–9096.
[14] T. Komuro, D. Mochizuko, H. Hashimoto, H. Tobita, Dalton Trans. 2022,
51, 9983–9987.
[15] a) K. Sato, T. Komuro, H. Hashimoto, H. Tobita, Chem. Lett. 2020,49,
1431–1434; b) K. Sato, T. Komuro, T. Osawa, H. Hashimoto, H. Tobita,
Organometallics 2022,41, 2612–2621.
[16] a) T. Sato, H. Tobita, H. Ogino, Chem. Lett. 2001, 854–855; b) T. Sato, M.
Okazaki, H. Tobita, H. Ogino, J. Organomet. Chem. 2003,669, 189–199;
c) T. Sato, M. Okazaki, H. Tobita, Chem. Lett. 2004, 868–869.
[17] Y. Kanno, T. Komuro, H. Tobita, Organometallics 2015,34, 3699–3705.
[18] W.-H. Kwok, G.-L. Lu, C. E. F. Rickard, W. R. Roper, L. J. Wright, J.
Organomet. Chem. 2004,689, 2979–2987.
[19] J. Guzmán, P. García-Orduña, V. Polo, F. J. Lahoz, L. A. Oro, F. J.
Fernández-Alvarez, Catal. Sci. Technol. 2019,9, 2858–2867.
[20] J. Guzmán, A. M. Bernal, P. García-Orduña, F. J. Lahoz, V. Polo, F. J.
Fernández-Alvarez, Dalton Trans. 2020,49, 17665–17673.
[21] J. Guzmán, A. M. Bernal, P. García-Orduña, F. J. Lahoz, L. A. Oro, F. J.
Fernández-Alvarez, Dalton Trans. 2019,48, 4255–4262.
[22] J. Guzmán, P. García-Orduña, F. J. Lahoz, F. J. Fernández-Alvarez, RSC
Adv. 2020,10, 9582–9586.
[23] J. Guzmán, A. Urriolabeitia, M. Padilla, P. García-Orduña, V. Polo, F. J.
Fernández-Alvarez, Inorg. Chem. 2022,61, 20216–20221.
[24] a) R. Lalrempuia, M. Iglesias, V. Polo, P. J. Sanz Miguel, F. J. Fernández-
Alvarez, J. J. Pérez-Torrente, L. A. Oro, Angew. Chem. Int. Ed. 2012,51,
12824–12827; b) A. Julián, E. A. Jaseer, K. Garcés, F. J. Fernández-Alvarez,
P. García-Orduña, F. J. Lahoz, L. A. Oro, Catal. Sci. Technol. 2016,6, 4410–
4417; c) A. Julián, J. Guzmán, E. A. Jaseer, F. J. Fernández-Alvarez, R.
Royo, V. Polo, P. García-Orduña, F. J. Lahoz, L. A. Oro, Chem. Eur. J. 2017,
23, 11898–11907.
[25] J. Guzmán, A. Torguet, P. García-Orduña, F. J. Lahoz, L. A. Oro, F. J.
Fernández-Alvarez, J. Organomet. Chem. 2019,897, 50–56.
[26] A. Gómez-España, P. García-Orduña, J. Guzmán, I. Fernández, F. J.
Fernández-Alvarez, Inorg. Chem. 2022,61, 16282–16294.
[27] a) A. Gomez-España, J. L. Lopez-Morales, B. Español-Sanchez, P. García-
Orduña, F. J. Lahoz, M. Iglesias, F. J. Fernández-Alvarez, Dalton Trans.
2023,52, 6722–6729; b) A. Gomez-España, J. L. Lopez-Morales, B.
Español-Sanchez, P. García-Orduña, F. J. Lahoz, M. Iglesias, F. J.
Fernández-Alvarez, Dalton Trans. 2023,52, 11361–11362.
[28] J. Guzmán, A. Urriolabeitia, V. Polo, M. Fernández-Buenestado, M.
Iglesias, F. J. Fernández-Alvarez, Dalton Trans. 2022,51, 4386–4393.
[29] A. Gómez-España, P. García-Orduña, F. J. Lahoz, I. Fernández, F. J.
Fernández-Álvarez, Organometallics 2024,43, 402–413.
[30] Y. Shi, X. Li, T. Zheng, B. Xue, S. Zhang, H. Sun, O. Fuhr, D. Fenske, Inorg.
Chim. Acta 2017,455, 112–117.
[31] K. A. Smart, M. Grellier, L. Vendier, S. A. Mason, S. C. Capelli, A. Albinati,
S. Sabo-Etienne, Inorg. Chem. 2013,52, 2654–2661.
[32] T. D. Tilley. In The Chemistry of Orgainic Silicon. Compounds, S. Patai
and Z. Rappoport (Eds.); Chap 24, p. 1415, Wiley, New York, 1989.
[33] J. Grobe, A. Walter, J. Organomet. Chem. 1977,140, 325–348.
[34] R. D. Holmes-Smith, S. R. Stobart, T. S. Cameron, K. Jochem, J. Chem. Soc.
Chem. Commun. 1981, 937–939.
[35] R. Usui, Y. Sunada, Inorg. Chem. 2021,60, 15101–15105.
[36] J. Shen, R. Usui, Y. Sunada, Eur. J. Org. Chem. 2022, e202101563.
[37] A. García-Camprubí, M. Martín, E. Sola, Inorg. Chem. 2010,49, 10649–
10657.
[38] V. Montiel-Palma, O. Piechaczyk, A. Picot, A. Auffrant, L. Vendier, P.
Le Floch, S. Sabo-Etienne, Inorg. Chem. 2008,47, 8601–8603.
[39] Y.-J. Lee, J.-D. Lee, S.-J. Kim, S. Keum, J. Ko, I.-H. Suh, M. Cheong, S. O.
Kang, Organometallics 2004,23, 203–214.
[40] G. R. Clark, C. E. F. Rickard, W. R. Roper, D. M. Salter, L. J. Wright, Pure
Appl. Chem. 1990,62, 1039–1042.
[41] G. R. Clark, G.-L. Lu, C. E. F. Rickard, W. R. Roper, L. J. Wright, J. Organo-
met. Chem. 2005,690, 3309–3320.
[42] H. Wada, H. Tobita, H. Ogino, Organometallics 1997,16, 3870–3872.
[43] S. Xu, P. Zhang, X. Li, B. Xue, H. Sun, O. Fuhr, D. Fenske, Chem. Asian J.
2017,12, 1234–1239.
[44] Z. Xiong, X. Li, S. Zhang, Y. Shi, H. Sun, Organometallics 2016,35, 357–
363.
[45] P. Zhang, S. Xu, X. Li, X. Qi, H. Sun, O. Fuhr, D. Fenske, Polyhedron 2018,
143, 165–170.
[46] S. Ren, S. Xie, T. Zheng, Y. Wang, S. Xu, B. Xue, X. Li, H. Sun, O. Fuhr, D.
Fenske, Dalton Trans. 2018,47, 4352–4359.
[47] U. Prieto-Pascual, A. Rodríguez-Diéguez, Z. Freixa, M. A. Huertos, Inorg.
Chem. 2023,62, 3095–3105.
[48] B. Ghaffari, S. M. Preshlock, D. L. Plattner, R. J. Staples, P. E. Maligres,
S. W. Krska, R. E. Maleczka, M. R. III Smith, J. Am. Chem. Soc. 2014,136,
14345–14348.
[49] S. J. Mitton, R. McDonald, L. Turculet, Angew. Chem. Int. Ed. 2009,48,
8568–8571.
[50] A. J. Ruddy, S. J. Mitton, R. McDonald, L. Turculet, Chem. Commun. 2012,
48, 1159–1161.
[51] B. Yang, X. Tan, Y. Ge, Y. Li, C. He, Org. Chem. Front. 2023,10, 4862–
4870.
[52] S. Azpeitia, B. Fernández, M. A. Garralda, M. A. Huertos, Eur. J. Inorg.
Chem. 2015, 5451–5456.
[53] S. Azpeitia, M. A. Garralda, M. A. Huertos, ChemCatChem 2017,9, 1901–
1905.
[54] U. Prieto, S. Azpeitia, E. San Sebastian, Z. Freixa, M. A. Garralda, M. A.
Huertos, ChemCatChem 2021,13, 1403–1409.
[55] M. Zafar, R. Ramalakshmi, A. Ahmad, P. K. S. Antharjanam, S. Bontemps,
S. Sabo-Etienne, S. Ghosh, Inorg. Chem. 2021,60, 1183–1194.
[56] A. Sauermoser, T. Lainer, G. Glotz, F. Czerny, B. Schweda, R. C. Fischer, M.
Haas, Inorg. Chem. 2022,61, 14742–14751.
[57] Z. Ouyang, L. Deng, Organometallics 2013,32, 7268–7271.
Wiley VCH Donnerstag, 05.09.2024
2409 / 358665 [S. 99/100] 1
ChemPlusChem 2024,89, e202400162 (21 of 22) © 2024 The Authors. ChemPlusChem published by Wiley-VCH GmbH
ChemPlusChem
Review
doi.org/10.1002/cplu.202400162

[58] a) Z. Mo, Y. Liu, L. Deng, Angew. Chem. Int. Ed. 2013,52, 10845–10849;
b) Z. Mo, L. Deng, Synlett 2014,25, 1045–1049.
[59] J. Sun, C. Ou, C. Wang, M. Uchiyama, L. Deng, Organometallics 2015,34,
1546–1551.
[60] J. Sun, L. Luo, Y. Luo, L. Deng, Angew. Chem. Int. Ed. 2017,56, 2720–
2724.
[61] P. Ríos, H. Fouilloux, J. Díez, P. Vidossich, A. Lledós, S. Conejero, Chem.
Eur. J. 2019,25, 11346–11345.
[62] N. E. Poitiers, L. Giarrana, V. Huch, M. Zimmer, D. Scheschkewitz, Chem.
Sci. 2020,11, 7782–7788.
[63] P. Garg, A. Carpentier, I. Douair, D. Dange, Y. Jiang, K. Yuvaraj, L. Maron,
C. Jones, Angew. Chem. Int. Ed. 2022,61, e202201705.
[64] P. García-Orduña, I. Fernández, L. A. Oro, F. J. Fernández-Álvarez, Dalton
Trans. 2021,50, 5951–5959.
[65] a) E. Lukevics, P. Arsenyan, O. Pudova, Main Group Met. Chem. 2002,25,
415–436; b) E. Lukevics, P. Arsenyan, O. Pudova, Main Group Met. Chem.
2002,25, 541–560; c) E. Lukevics, O. Pudova, Main Group Met. Chem.
2000,23, 207–231; d) E. Lukevics, O. Pudova, Main Group Met. Chem.
1999,22, 385–403.
Manuscript received: February 29, 2024
Revised manuscript received: May 22, 2024
Accepted manuscript online: May 23, 2024
Version of record online: July 11, 2024
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