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ABSTRACT: A multidentate and flexible diolefin-diphosphine ligand, based on the dibenzylidene acetone core, namely dbaphos (1), is reported herein. The ligand adopts an array of different geometries at Pt, Pd and Rh. At Pt(II) the dbaphos ligand forms cis- and trans-diphosphine complexes and can be defined as a wide-angle spanning ligand. (1) H NMR spectroscopic analysis shows that the β-hydrogen of one olefin moiety interacts with the Pt(II) centre (an anagostic interaction), which is supported by DFT calculations. At Pd(0) and Rh(I) , the dbaphos ligand exhibits both olefin and phosphine interactions with the metal centres. The Pd(0) complex of dbaphos is dinuclear, with bridging diphosphines. The complex exhibits the coordination of one olefin moiety, which is in dynamic exchange (intramolecular) with the other "free" olefin. The Pd(0) complex of dbaphos reacts with iodobenzene to afford trans-[Pd(II) (dbaphos)I(Ph)]. In the case of Rh(I) , dbaphos coordinates to form a structure in which the phosphine and olefin moieties occupy both axial and equatorial sites, which stands in contrast to a related bidentate olefin, phosphine ligand ("Lei" ligand), in which the olefins occupy the equatorial sites and phosphines the axial sites, exclusively.
Chemistry 03/2013; · 5.93 Impact Factor
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ABSTRACT: Reactions of [ReH(5) (PMe(2) Ph)(3) ] with alkynols HC≡CC(OH)(R)C≡CSiMe(3) (R=tBu, iPr, 1-adamantyl) in the presence of HCl give the vinylcarbyne complexes [Re{≡CCHC(R)C≡CSiMe(3) }Cl(2) (PMe(2) Ph)(3) ], which react with tBuMgCl to give [Re{≡CCHC(R)C≡CSiMe(3) }HCl(PMe(2) Ph)(3) ]. Treatment of [Re{≡CCHC(R)C≡CSiMe(3) }HCl(PMe(2) Ph)(3) ] with nBu(4) NF gives [Re{≡CCHC(R)C≡CH}HCl(PMe(2) Ph)(3) ], which first isomerizes to the bicyclic complexes [Re{CHCHC(R)CCH}Cl(PMe(2) Ph)(3) ], and then to the rhenabenzynes [Re{≡CCHC(R)CHCH}Cl(PMe(2) Ph)(3) ]. The NMR spectroscopic and structural data as well as the aromatic stabilization energy (ASE) and nucleus-independent chemical-shift (NICS) values suggest that these rhenabenzynes have aromatic character.
Chemistry 09/2012; 18(44):14128-39. · 5.93 Impact Factor
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ABSTRACT: NHC meets F: NHC-bound enolates undergo a catalytic asymmetric fluorination reaction to β,γ-unsaturated α-fluoroesters, which are obtained with good efficiency and stereoselectivity (see scheme, NFSI=N-fluorobenzenesulfonimide). The strategy overcomes possible challenges, such as fluorination in the γ position and difluorination. Experimental evidence combined with DFT calculations provides insight into the reaction mechanism.
Angewandte Chemie International Edition 09/2012; 51(41):10359-63. · 13.45 Impact Factor
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ABSTRACT: The use of diethynylsilane, diethynyldisilane and diethynyldisiloxane in the synthesis of some linked metal carbonyl clusters
is demonstrated. New dimeric η2-diyne complexes of cobalt [{Co2(CO)6}2(η2-diyne)], ruthenium [{(μ-H)Ru3(CO)9}2(μ3-η2,η2-diyne)] and osmium [{(μ-CO)Os3(CO)9}2(μ3-η2-diyne)] {diyne=HC≡CSi(CH3)2C≡CH, HC≡CSi(CH3)2–Si(CH3)2C≡CH, HC≡CSi(CH3)2–O–Si(CH3)2C≡CH or HC≡CSi(Ph)2C≡CH} have been prepared in good yields from the reaction of [Co2(CO)8], [Ru3(CO)12] and [Os3(CO)10(NCMe)2] with half an equivalent of the appropriate diyne ligand, respectively. All the twelve compounds have been characterized
by IR and 1H NMR spectroscopies and mass spectrometry. The molecular structures of eight of them have been determined by X-ray crystallography.
Structurally, each of the tetracobalt species displays two Co2C2 cores adopting the pseudo-tetrahedral geometry with the alkyne bond lying essentially perpendicular to the Co–Co vector.
For the group 8 ruthenium and osmium analogues, the hexanuclear carbonyl clusters consist of two trinuclear metal cores with
the μ3-η2,η2 bonding mode for the acetylene groups in the former case and μ3-(η2-||) bonding mode in the latter one. Density functional theory was employed to study the electronic structures of these molecules
in terms of the nature of the silyl or disilyl unit and its substituents.
KeywordsAlkynes-Cobalt-Crystal structures-Osmium-Ruthenium
Journal of Cluster Science 05/2012; 21(3):461-484. · 0.92 Impact Factor
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ABSTRACT: Transition metals such as Fe in porphyrin complexes are known to bind or react with O2, and such reactions are critical to many biological functions and catalytic oxidation using O2. The transition metals in these reactions often contain valence d electrons, and oxidation of metals is an important step.
In recent years, reactions of O2 with d0 transition metal complexes such as Hf(NR2)4 (R = alkyl) have been used to make metal oxide thin films as insulating gate materials in new microelectronic devices. This
feature article discusses our recent studies of such reactions and the formation of TiO2 thin films. In contrast to the reactions of many d
n
complexes where metals are often oxidized, reactions of d0 complexes such as Hf(NMe2)4 and Ta(NMe2)4(SiR3) with O2 usually lead to the oxidation of ligands, forming, e.g., -ONMe2 and -OSiR3 from -NMe2 and -SiR3 ligands, respectively. Mechanistic and theoretical studies of these reactions have revealed pathways in the formation of
the metal oxide thin films as microelectronic materials.
Science in China Series B Chemistry 04/2012; 52(11):1723-1733. · 1.20 Impact Factor
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ABSTRACT: Extended Hückel Theory (EHT) and Density Functional Theory (DFT) calculations on hexacapped cubic aluminum clusters of the
type [(AlH)8(μ4-CH)6−n
(μ4-H)
n
]+/−q (n≤6) indicate that their favored number of skeletal electron pairs (SEP), 12 SEPs for n≥3, 14 SEPs for n=2, 16 SEPs for n=1 and 18 SEPs for n=0, depends on the relative number of the two types of capping ligands: one-orbital ligands such as H and conical three-orbital
CH units. Although only 16- and 18-SEP species have been isolated so far, DFT calculations indicate that 14-SEP clusters of
the type [(AlR′)8(μ4-CR)4(μ4-X)2]2+ (X=one-orbital ligand) should be synthesized. Computed 12-SEP models were not found to be energy minima, but this should
not preclude the possibility for stabilizing such species, for example with bulky substituents. Changing the CR capping ligands
into AlR units in the above series is expected to limit their electron counts to 12 SEPs. The incorporation of a main-group
atom in the middle of the cube does not change the favored cluster electron count. However, calculations indicate that only
12-SEP species are likely to be synthesized.
Journal of Cluster Science 04/2012; 18(1):271-288. · 0.92 Impact Factor
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ABSTRACT: The Lewis base adduct of B(2)pin(2) and the NHC (1,3-bis(cyclohexyl)imidazol-2-ylidene), which was proposed to act as a source of nucleophilic boryl groups in the β-borylation of α,β-unsaturated ketones, has been isolated, and its solid state structure and solution behavior was studied. In solution, the binding is weak, and NMR spectroscopy reveals a rapid exchange of the NHC between the two boron centers. DFT calculations reveal that the exchange involves dissociation and reassociation of NHC rather than an intramolecular process.
The Journal of Organic Chemistry 11/2011; 77(1):785-9. · 4.45 Impact Factor
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ABSTRACT: Silver- and copper-catalyzed decarboxylation reactions of aryl carboxylic acids were investigated with the aid of density functional theory calculations. The reaction mechanism starts with a carboxylate complex of silver or copper. Decarboxylation occurs via ejecting CO(2) from the carboxylate complex followed by protodemetallation with an aryl carboxylic acid molecule to regenerate the starting complex. Our results indicated that the primary factor to affect the overall reaction barriers is the ortho steric destabilization effect on the starting carboxylate complexes for most cases. Certain ortho substituents that are capable of coordinating with the catalyst metal center without causing significant ring strain stabilize the decarboxylation transition states and reduce the overall reaction barriers. However, the coordination effect is found to be the secondary factor when compared with the ortho effect.
Dalton Transactions 11/2011; 40(44):11926-36. · 3.84 Impact Factor
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ABSTRACT: The electrophilic substitution reactions of metallabenzynes Os(≡CC(R)═C(CH(3))C(R)═CH)Cl(2)(PPh(3))(2) (R = SiMe(3), H) were studied. These metallabenzynes react with electrophilic reagents, including Br(2), NO(2)BF(4), NOBF(4), HCl/H(2)O(2), and AlCl(3)/H(2)O(2) to afford the corresponding bromination, nitration, nitrosation, and chlorination products. The reactions usually occur at the C2 and C4 positions of the metallacycle. These observations support the notion that metallabenzynes exhibit aromatic properties.
Journal of the American Chemical Society 11/2011; 133(45):18350-60. · 9.91 Impact Factor
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ABSTRACT: Reaction of [(IPr)Cu-OtBu] (1) with pinB-SiMe(2)Ph (2) leads to the Cu-silyl complex [(IPr)Cu-SiMe(2)Ph] (3). Insertion of CO(2) into the Cu-Si bond of 3 is followed by transformation of the resulting silanecarboxy complex [(IPr)Cu-O(2)CSiMe(2)Ph] (4) to the silanolate complex [(IPr)Cu-OSiMe(2)Ph] (5) via extrusion of CO. As 5 reacts readily with 2 to regenerate 3, a catalytic CO(2) reduction to CO is feasible. The individual steps were studied by in situ(13)C NMR spectroscopy of a series of stoichiometric reactions. Complexes 3, 4, and 5 were isolated and fully characterized, including single-crystal X-ray diffraction studies. Interestingly, the catalytic reduction of CO(2) using silylborane 2 as a stoichiometric reducing agent leads not only to CO and pinB-O-SiMe(2)Ph but also to PhMe(2)Si-CO(2)-SiMe(2)Ph as an additional reduction product.
Journal of the American Chemical Society 11/2011; 133(47):19060-3. · 9.91 Impact Factor
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Angewandte Chemie International Edition 09/2011; 50(45):10675-8. · 13.45 Impact Factor
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ABSTRACT: The thermodynamic and kinetic aspects of the rearrangement reactions of a series of metallabenzenes to cyclopentadienyl complexes have been investigated by DFT computational study in order to reveal how substituents on the metallacycle, ligands around the metal center, and metals affect the transformation. We found that substitutents and their locations on the metallacycle have a significant effect on the thermodynamics and kinetics of the rearrangement reactions.
Dalton Transactions 08/2011; 40(42):11315-20. · 3.84 Impact Factor
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ABSTRACT: A new trinuclear species containing a Ta(IV)-Ta(IV) bond, Ta(3)(μ-H)(μ-NMe(2))(μ=NBu(t))(2)(=NBu(t))(NMe(2))(5), has been formed by reductive elimination of H(2). Ta(2)H(2)(μ-NMe(2))(2)(NMe(2))(2)(=NBu(t))(2) has also been isolated. O(2) oxidizes the Ta(IV)-Ta(IV) bond to yield Ta(3)(μ(3)-O)(H)(μ=NBu(t))(μ-NMe(2))(2)(NMe(2))(4)(=NBu(t))(2) under ligand exchange. Delocalization of d electrons is discussed.
Chemical Communications 07/2011; 47(30):8685-7. · 6.17 Impact Factor
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Angewandte Chemie International Edition 06/2011; 50(32):7295-9. · 13.45 Impact Factor
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ABSTRACT: Decarboxylation process in a series of PdL(2)X(η(2)-OOCAr(R)) complexes 2OS(R) (L = DMSO; X = OOCCF(3)(-); R = H, OMe, NO(2), Me and CN) with substituent R at an ortho, meta or para position were investigated with the aid of density functional theory calculations. Through our study, we found that the OOCCF(3)(-) ligand is not just a spectator ligand but assists the decarboxylation process. The results indicated that electron-donating substituents have greater promotion effect than electron-withdrawing substituents on the decarboxylation process. An ortho substituent in the substrate ligands OOCAr(R)(-) is normally necessary for a successful decarboxylation. The reason behind this has been explained.
Dalton Transactions 11/2010; 39(41):9815-22. · 3.84 Impact Factor
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ABSTRACT: 4-(2-Phenylethynyl)-2H-chromen-2-one reacts with norbornene and Co(2)(CO)(8) in an intermolecular Pauson-Khand reaction by focused microwave dielectric heating. Two regioisomeric products are formed; the electron-deficient coumarin moiety preferentially occupies the β-position of the cyclopentenone ring system, whereas the phenyl occupies the α-position. The sterically hindered α,β-(2,3)-disubstituted cyclopentenone regioisomeric products exhibit pronounced atropisomerisation, and the magnitude of the energetic barrier to interconversion between these atropisomers is dependent on the relative position of the coumarin moieties. Interconversion is slow when the coumarin is found in the α-position, whereas interconversion is relatively fast when found in the β-position.
Organic & Biomolecular Chemistry 09/2010; 8(23):5398-403. · 3.70 Impact Factor
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Advanced Synthesis & Catalysis 05/2010; 352(9):1512 - 1522. · 6.05 Impact Factor
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ABSTRACT: Treatment of the rhenium polyhydride complex ReH5(PMe2Ph)3 with HC≡CR (R = Ph, SiMe3, (CH2)4Me) in the presence of 2.2 equiv of HCl produces a mixture of the carbyne complexes Re(≡CCH2R)Cl2(PMe2Ph)3 and the η2-vinyl complexes Re(η2-CH2CR)Cl2(PMe2Ph)3. When HC≡CC(OH)Ph2 was used, the reaction gave the carbyne complexes Re(≡CCH═CPh2)Cl2(PMe2Ph)3 and Re(≡CCH2C(OH)Ph2)Cl2(PMe2Ph)3 along with the η2-vinyl complex Re(η2-CH2CC(OH)Ph2)Cl2(PMe2Ph)3.
05/2010;
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Zhenyang Lin
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ABSTRACT: Computational and theoretical chemistry provide fundamental insights into the structures, properties, and reactivities of molecules. As a result, theoretical calculations have become indispensable in various fields of chemical research and development. In this Account, we present our research in the area of computational transition metal chemistry, using examples to illustrate how theory impacts our understanding of experimental results and how close collaboration between theoreticians and experimental chemists can be mutually beneficial. We begin by examining the use of computational chemistry to elucidate the details of some unusual chemical bonds. We consider the three-center, two-electron bonding in titanocene sigma-borane complexes and the five-center, four-electron bonding in a rhodium-bismuth complex. The bonding in metallabenzene complexes is also examined. In each case, theoretical calculations provide particular insight into the electronic structure of the chemical bonds. We then give an example of how theoretical calculations aided the structural determination of a kappa(2)-N,N chelate ruthenium complex formed upon heating an intermediate benzonitrile-coordinated complex. An initial X-ray diffraction structure proposed on the basis of a reasonable mechanism appeared to fit well, with an apparently acceptable R value of 0.0478. But when DFT calculations were applied, the optimized geometry differed significantly from the experimental data. By combining experimental and theoretical outlooks, we posited a new structure. Remarkably, a re-refining of the X-ray diffraction data based on the new structure resulted in a slightly lower R value of 0.0453. We further examine the use of computational chemistry in providing new insight into C-H bond activation mechanisms and in understanding the reactivity properties of nucleophilic boryl ligands, addressing experimental difficulties with calculations and vice versa. Finally, we consider the impact of theoretical insights in three very specific experimental studies of chemical reactions, illustrating how theoretical results prompt further experimental studies: (i) diboration of aldehydes catalyzed by copper(I) boryl complexes, (ii) ruthenium-catalyzed C-H amination of arylazides, and (iii) zinc reduction of a vinylcarbyne complex. The concepts and examples presented here are intended for nonspecialists, particularly experimentalists. Together, they illustrate some of the achievements that are possible with a fruitful union of experiment and theory.
Accounts of Chemical Research 05/2010; 43(5):602-11. · 21.64 Impact Factor
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ABSTRACT: Palladium-catalysed processes for the formation of carbon-carbon bonds, i.e., coupling reactions of organic halides (R(1)X) and main-group organometallic compounds (R(2)M) are most frequently applied in synthesizing biologically and pharmaceutically important organic molecules. In this article, we provide a critical review on theoretical studies of the palladium-catalysed carbon-carbon cross-coupling reactions, and give an up-to-date summary of the current understanding of the cross-coupling reactions from a theoretical point of view (108 references).
Chemical Society Reviews 05/2010; 39(5):1692-705. · 28.76 Impact Factor
