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ABSTRACT: Formally, triple-bonded dimetallynes ArEEAr [E = Ge (1), Sn (2); Ar = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)] have been previously shown to activate aliphatic, allylic C-H bonds in cyclic olefins, cyclopentadiene (CpH), cyclopentene (c-C(5)H(8)) and 1,4-cyclohexadiene, with intriguing selectivity. In the case of the five-membered carbocycles, cyclopentadienyl species ArECp [E = Ge (3), Sn (4)] are formed. In this study, we examine the mechanisms for activation of CpH and c-C(5)H(8) using experimental methods and describe a new product found from the reaction between 1 and c-C(5)H(8), an asymmetrically substituted digermene ArGe(H)Ge(c-C(5)H(9))Ar (5), crystallized in 46% yield. This compound contains a hydrogenated cyclopentyl moiety and is found to be produced in a 3:2 ratio with 3, explaining the fate of the liberated H atoms following triple C-H activation. We show that when these C-H activation reactions are carried out in the presence of tert-butyl ethylene (excess), compounds {ArE(CH(2)CH(2)tBu)}(2) [E = Ge(8), Sn(9)] are obtained in addition to ArECp; in the case of CpH, the neohexyl complexes replace the production of H(2) gas, and for c-C(5)H(8) they displace cyclopentyl product 5 and account for all the hydrogen removed in the dehydroaromatization reactions. To confirm the source of 8 and 9, it was demonstrated that these molecules are formed cleanly between the reaction of (ArEH)(2) [E = Ge(6), Sn(7)] and tert-butyl ethylene, new examples of noncatalyzed hydro-germylation and -stannylation. Therefore, the presence of transient hydrides of the type 6 and 7 can be surmised to be reactive intermediates in the production of 3 and 4, along with H(2), from 1 and 2 and CpH (respectively), or the formation of 3 and 5 from 1. The reaction of 6 or 7 with CpH gave 3 or 4, respectively, with concomitant H(2) evolution, demonstrating the basic nature of these low-valent group 14 element hydrides and their key role in the 'cascade' of C-H activation steps. Additionally, during the course of these studies a new polycyclic compound (ArGe)(2)(C(7)H(12)) (10) was obtained in 60% yield from the reaction of 1,6-heptadiene and 1 via double [2 + 2] cycloaddition and gives evidence for a nonradical mechanism for these types of reactions.
Journal of the American Chemical Society 08/2012; 134(35):14595-603. · 9.91 Impact Factor
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ABSTRACT: The heavier group 13 element alkene analogue, digallene Ar(iPr(4))GaGaAr(iPr(4)) (1) [Ar(iPr(4)) = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)], has been shown to react readily in [n + 2] (n = 6, 4, 2 + 2) cycloaddition reactions with norbornadiene and quadricyclane, 1,3,5,7-cyclooctatetraene, 1,3-cyclopentadiene, and 1,3,5-cycloheptatriene to afford the heavier element deltacyclane species Ar(iPr(4))Ga(C(7)H(8))GaAr(iPr(4)) (2), pseudoinverse sandwiches Ar(iPr(4))Ga(C(8)H(8))GaAr(iPr(4)) (3, 3(iso)), and polycyclic compounds Ar(iPr(4))Ga(C(5)H(6))GaAr(iPr(4)) (4) and Ar(iPr(4))Ga(C(7)H(8))GaAr(iPr(4)) (5, 5(iso)), respectively, under ambient conditions. These reactions are facile and may be contrasted with other all-carbon versions, which require transition-metal catalysis or forcing conditions (temperature, pressure), or with the reactions of the corresponding heavier group 14 species Ar(iPr(4))EEAr(iPr(4)) (E = Ge, Sn), which give very different product structures. We discuss several mechanistic possibilities, including radical- and non-radical-mediated cyclization pathways. These mechanisms are consistent with the improved energetic accessibility of the LUMO of the heavier group 13 element multiple bond in comparison with that of a simple alkene or alkyne. We show that the calculated frontier molecular orbitals (FMOs) of Ar(iPr(4))GaGaAr(iPr(4)) are of π-π symmetry, allowing this molecule to engage in a wider range of reactions than permitted by the usual π-π* FMOs of C-C π bonds or the π-n(+) FMOs of heavier group 14 alkyne analogues.
Journal of the American Chemical Society 03/2012; 134(16):7155-64. · 9.91 Impact Factor
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Angewandte Chemie International Edition 09/2011; 50(46):10965-8. · 13.45 Impact Factor
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ABSTRACT: Treatment of the dimetallynes Ar'EEAr' [E = Ge, Sn; Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-iPr(2))(2)] with a cyclic olefin-cyclopentadiene (CpH), cyclopentene, 1,4-cyclohexadiene (CHD), or cyclohexene-showed that, with the exception of cyclohexene, they react readily, affording C-H activation at room temperature. Reaction of the digermyne and distannyne with CpH gave the cyclopentadienyl anion, which is bound in a π-fashion to a mononuclear group 14 element center, along with evolution of hydrogen gas. Unusually, the digermyne also reacted with cyclopentene to give the same dehydroaromatization product, formed from triple C-H activation/dehydrogenation. It also was found to react with CHD to give a mixture of (Ar'GeH)(2), benzene, and a new 7-germanorbornadiene species bound to a cyclohex-2-enyl fragment.
Journal of the American Chemical Society 08/2011; 133(31):11960-3. · 9.91 Impact Factor
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ABSTRACT: The reactions of Ar'GaGaAr' (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)) with alkenes revealed the addition of two olefins per Ar'GaGaAr' under ambient conditions for ethylene, propene, 1-hexene and styrene but no reactions with more hindered or cyclic olefins.
Chemical Communications 07/2011; 47(26):7506-8. · 6.17 Impact Factor
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ABSTRACT: The molecular and electronic structures and bonding analysis of terminal cationic metal-ylyne complexes (MeCN)(PMe(3))(4)M≡EMes](+) (M = Mo, W; E = Si, Ge, Sn, Pb) were investigated using DFT/BP86/TZ2P/ZORA level of theory. The calculated geometrical parameters for the model complexes are in good agreement with the reported experimental values. The M-E σ-bonding orbitals are slightly polarized toward E except in the complex [(MeCN)(PMe(3))(4)W(SnMes)](+), where the M-E σ-bonding orbital is slightly polarized toward the W atom. The M-E π-bonding orbitals are highly polarized toward the metal atom. In all complexes, the π-bonding contribution to the total M≡EMes bond is greater than that of the σ-bonding contribution and increases upon going from M = Mo to W. The values of orbital interaction ΔE(orb) are significantly larger in all studied complexes I-VIII than the electrostatic interaction ΔE(elstat). The absolute values of the interaction energy, as well as the bond dissociation energy, decrease in the order Si > Ge > Sn > Pb, and the tungsten complexes have stronger bonding than the molybdenum complexes.
Inorganic Chemistry 06/2011; 50(15):7080-9. · 4.60 Impact Factor
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Philip P Power
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ABSTRACT: We showed in 2005 that a digermyne, a main group compound with a digermanium core and aromatic substituents, reacted directly with hydrogen at 25 °C and 1 atm to give well-defined hydrogen addition products. This was the first report of a reaction of main group molecules with hydrogen under ambient conditions. Our group and a number of others have since shown that several classes of main group molecules, either alone or in combination, react directly (in some cases reversibly) with hydrogen under mild conditions. Moreover, this reactivity was not limited to hydrogen but also included direct reactions with other important small molecules, including ammonia, boranes, and unactivated olefins such as ethylene. These reactions were largely unanticipated because main group species were generally considered to be too unreactive to effect such transformations. In this Account, we summarize recent developments in the reactions of the multiple bonded and other open shell derivatives of the heavier main group elements with hydrogen, ammonia, olefins, or related molecules. We focus on results generated primarily in our laboratory, which are placed in the context of parallel findings by other researchers. The close relationship between HOMO-LUMO separations, symmetry considerations, and reactivity of the open shell in main group compounds is emphasized, as is their similarity in reactivity to transition metal organometallic compounds. The unexpectedly potent reactivity of the heavier main group species arises from the large differences in bonding between the light and heavy elements. Specifically, the energy levels within the heavier element molecules are separated by much smaller gaps as a result of generally lower bond strengths. In addition, the ordering and symmetries of the energy levels are generally different for their light counterparts. Such differences lie at the heart of the new reactions. Moreover, the reactivity of the molecules can often be interpreted qualitatively in terms of simple molecular orbital considerations. More quantitative explanations are accessible from increasingly sophisticated density functional theory (DFT) calculations. We open with a short description of the background developments that led to this work. These advances involved the synthesis and characterization of numerous new main group molecules involving multiple bonds or unsaturated configurations; they were pursued over the latter part of the last century and the beginning of the new one. The results firmly established that the structures and bonding in the new compounds differed markedly from those of their lighter element congeners. The knowledge gained from this fundamental work provided the framework for an understanding of their structures and bonding, and hence an understanding of the reactivity of the compounds discussed here.
Accounts of Chemical Research 06/2011; 44(8):627-37. · 21.64 Impact Factor
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ABSTRACT: Reaction of a digermyne with cyclooctatetraene (cot) gave two isomeric products. A Ge(II) inverse sandwich is formed as the kinetic product, which was a result of complete Ge≡Ge bond cleavage and the formation of a π-bound cot ring. This isomerized in solution at room temperature over a period of 5 days to give the thermodynamic product, a tetracyclic diene-digermane, in which a single-bonded Ge-Ge moiety has inserted into a C═C bond of the cot carbocycle. Kinetic studies afforded an activation enthalpy (ΔH(‡)) and entropy (ΔS(‡)) of 14.9 kcal mol(-1) and -6.2 cal mol(-1) K(-1) respectively. Heating crystals of the thermodynamic product at ca. 120 °C cleanly regenerated the original inverse sandwich isomer.
Journal of the American Chemical Society 12/2010; · 9.91 Impact Factor
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ABSTRACT: A series of first row transition metal complexes with unsupported M-Fe bonds, (3,5-(i)Pr(2)-Ar*)MFe(η(5)-C(5)H(5))(CO)(2) (M = Fe (1), Mn (2), Cr (3), 3,5-(i)Pr(2)-Ar* = -C(6)H-2,6-(C(6)H(2)-2,4,6-(i)Pr(3))(2)-3,5-(i)Pr(2)), was synthesized by salt metathesis. They were characterized by (1)H NMR, UV-vis spectroscopy, X-ray crystallography, and SQUID magnetic measurements. Two distinct Fe atoms in 1 were confirmed by Mössbauer spectroscopy. All three compounds feature short metal-metal bond distances (Fe-Fe, 2.3931(8) Å (1); Mn-Fe, 2.4512(5) Å (2); Cr-Fe, 2.4887(5) Å (3)). Their DFT computed structures were in excellent agreement with the experimental data and revealed a dative bonding interaction between the metals.
Journal of the American Chemical Society 11/2010; · 9.91 Impact Factor
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ABSTRACT: The synthesis and characterization of the series of organotin formates together with their thermolytic behavior are described. The diformate Bu(n)(2)Sn{OC(O)H}(2) (1) was synthesized by the reaction of Bu(n)(2)SnH(2) with formic acid. The triorganotin monoformate compounds R(3)SnOC(O)H (R = Cy (cyclohexyl)) 3, Mes, (mesityl, 2,4,6-trimethylphenyl) 4, and Dmp (2,6-dimethylphenyl 5) were obtained by the reaction of R(3)SnOH with formic acid. Their X-ray crystal structures along with that of the previously reported formate (PhCH(2))(3)SnOC(O)H (2) were determined. The diformate 1 exhibits an extended two-dimensional polymeric structure in which six-coordinate tin centers are linked by formate bridges. The tribenzyltin formate (2) possesses a chain structure in which the five-coordinate Sn(CH(2)Ph)(3) units are bridged by formate ions. The cyclohexyl derivative 3 was observed to have a similar structure. In contrast, the Mes and Dmp derivatives 4 and 5 support monomeric structures in which the four-coordinate tin atom is bound to an oxygen of the formate ligand. Heating the compounds in various high boiling solvents produced no decomposition up to 120 °C in the case of 1 and refluxing a solution of 2 or 3 in mesitylene or diglyme left the starting material mostly unchanged, although 3 decomposed to an insoluble orange solid in refluxing decalin. In contrast, the heating of 4 and 5 in refluxing mesitylene led to elimination of CO to give the tin hydroxides. The results are in contrast to the known thermolytic behavior of R(3)SnOC(O)H (R = Pr(n) or Bu(n)) complexes, which eliminate CO(2) to generate R(3)SnH. Compounds 3-5 are rare examples of structurally characterized tin formates.
Dalton Transactions 10/2010; 39(44):10659-63. · 3.84 Impact Factor
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ABSTRACT: Reaction of {Li(THF)Ar'MnI(2)}(2) (Ar' = C(6)H(3)-2,6-(C(6)H(2)-2,6-(i)Pr(3))(2)) with LiAr', LiC≡CR (R = (t)Bu or Ph), or (C(6)H(2)-2,4,6-(i)Pr(3))MgBr(THF)(2) afforded the diaryl MnAr'(2) (1), the alkynyl salts Ar'Mn(C≡C(t)Bu)(4){Li(THF)}(3) (2) and Ar'Mn(C≡CPh)(3)Li(3)(THF)(Et(2)O)(2)(μ(3)-I) (3), and the manganate salt {Li(THF)}Ar'Mn(μ-I)(C(6)H(2)-2,4,6-(i)Pr(3)) (4), respectively. Complex 4 reacted with one equivalent of (C(6)H(2)-2,4,6-(i)Pr(3))MgBr(THF)(2) to afford the homoleptic dimer {Mn(C(6)H(2)-2,4,6-(i)Pr(3))(μ-C(6)H(2)-2,4,6-(i)Pr(3))}(2) (5), which resulted from the displacement of the bulkier Ar' ligand in preference to the halogen. The reaction of the more crowded {Li(THF)Ar*MnI(2)}(2) (Ar* = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-(i)Pr(3))(2)) with Li(t)Bu gave complex Ar*Mn(t)Bu (6). Complex 1 is a rare monomeric homoleptic two-coordinate diaryl Mn(II) complex; while 6 displays no tendency to eliminate β-hydrogens from the (t)Bu group because of the stabilization supplied by Ar*. Compounds 2 and 3 have cubane frameworks, which are constructed from a manganese, three carbons from three acetylide ligands, three lithiums, each coordinated by a donor, plus either a carbon from a further acetylide ligand (2) or an iodide (3). The Mn(II) atom in 4 has an unusual distorted T-shaped geometry while the dimeric 5 features trigonal planar manganese coordination. The chloride substituted complex Li(2)(THF)(3){Ar'MnCl(2)}(2) (7), which has a structure very similar to that of {Li(THF)Ar'MnI(2)}(2), was also prepared for use as a possible starting material. However, its generally lower solubility rendered it less useful than the iodo salt. Complexes 1-7 were characterized by X-ray crystallography and UV-vis spectroscopy. Magnetic studies of 2-4 and 6 showed that they have 3d(5) high-spin configurations.
Dalton Transactions 10/2010; 39(44):10664-70. · 3.84 Impact Factor
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ABSTRACT: The reaction of a digermyne Ar'GeGeAr' (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2)) with AgSbF(6) at -40 °C forms the complex (AgAr'GeGeAr')(+)SbF(6)(-), which provides the first example of a heavier group 14 element alkyne analogue behaving as a π donor to a transition metal. The cation (AgAr'GeGeAr')(+) is best described as a hybrid of a π-complex and a σ-metallacyclopropene structure.
Journal of the American Chemical Society 09/2010; 132(38):13150-1. · 9.91 Impact Factor
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ABSTRACT: Reaction of M{N(SiMe(3))(2)}(2) (M = Ge, Sn, or Pb) with the sterically encumbered primary phosphine Ar'PH(2) (2), Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2)), at ca. 200 °C afforded the highly colored phosphinidene dimers {M(μ-PAr')}(2), M = Ge(3), Sn(4), or Pb(5), with disilylamine elimination. The compounds were characterized by single-crystal X-ray crystallography and heteronuclear NMR spectroscopy. The structures of 3, 4, and 5 featured similar M(2)P(2) ring cores, of which 4 and 5 have 50/50 P atom disorder, consistent with either a planar four-membered M(2)P(2) arrangement with anti aryl groups or with an M(2)P(2) ring folded along the M-M axis with syn aryl groups. A syn-folded structure was resolved for the Ge(2)P(2) ring in compound 3. The M-P distances resembled those in M(II) phosphido complexes and are consistent with single bonding. The coordination geometries at the phosphorus atoms are pyramidal. DFT calculations on the gas phase models {M(μ-PMe)}(2) (M = Ge, Sn, Pb) agreed with the syn (M-M folded) structural interpretation of the X-ray data. The synthesis of the bulky phosphine Ar'PH(2) 2 with the use of the aryl transfer agent Ar'MgBr(THF)(2) is also reported. This route afforded a significantly higher yield of product than that which was obtained using LiAr', which tends to result in aryl halide elimination and the observation of insoluble red phosphorus.
Inorganic Chemistry 09/2010; 49(18):8481-6. · 4.60 Impact Factor
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ABSTRACT: The solvent-free reaction of M{N(SiMe(3))(2)}(2) (M = Ge, Sn, or Pb) with the sterically encumbered primary amine 2,6-dimesitylaniline Ar(#)NH(2) [Ar(#) = C(6)H(3)-2,6(C(6)H(2)-2,4,6-Me(3))(2)] at ca. 165-175 degrees C afforded the highly colored imido dimers {M(mu-NAr(#))}(2), where M = Ge (1), Sn (2), or Pb (3), with disilylamine elimination. The compounds were characterized by single-crystal X-ray crystallography and heteronuclear NMR spectroscopy. The structures of 1-3 were very similar and had nonplanar four-membered M(2)N(2) ring cores that are folded along the M---M axis. The nitrogen atoms are planar-coordinated, and the M-N distances are consistent with single bonding. The reaction of M{N(SiMe(3))(2)}(2) with Ar(#)NH(2) in a 2:1 ratio in solution at lower temperature afforded the relatively stable monomeric primary amido species M{N(H)Ar(#)}(2), where M = Ge (4), Sn (5), or Pb (6). Complexes 4-6 displayed V-shaped MN(2) structures, and 5 and 6 revealed close approaches between the metal atom and ipso-carbon atoms of two flanking Mes groups of the terphenyl substituents [Sn(II)---C (2.957 A) and Pb(II)---C (2.965 A)]. The secondary metal-ligand interactions exerted large effects on their electronic and NMR spectra.
Inorganic Chemistry 08/2010; 49(15):7097-105. · 4.60 Impact Factor
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Chemical Reviews 07/2010; 110(7):3877-923. · 40.20 Impact Factor
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ABSTRACT: The reaction of (Ar′SnCl)2 (Ar′ = −C6H3-2,6-(C6H3-2,6-iPr2)2) with LiC≡CR (R = SiMe3 or tBu) afforded the orange-red, alkynyl-substituted, symmetric distannene Ar′(Me3SiC≡C)SnSn(C≡CSiMe3)Ar′ (1) or the blue unsymmetric stannylstannylene Ar′SnSn(C≡CtBu)2Ar′ (2), respectively, whose structures were determined by X-ray crystallography. In solution at room temperature, however, both compounds have very similar UV−vis and 1H NMR spectra, consistent with the formation of monomeric stannylene units. Cooling a solution of 1 resulted in a color change to pink and the appearance of a new UV−vis absorption at 506 nm, consistent with the formation of a symmetric dimeric structure at low temperature. The different structures of 1 and 2 in the solid state are probably a result of packing effects. In contrast, the analogous reactions of (Ar′GeCl)2 with LiC≡CR (R = SiMe3 or tBu) resulted in the exclusive formation of digermene derivatives Ar′(RC≡C)GeGe(C≡CR)Ar′ (R = SiMe3 (3), tBu (4)), which maintain their dimeric structures in solution.
07/2010;
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ABSTRACT: The synthesis and characterization of two-coordinate cobalt(ii) complexes CoAr'(2) (1) and Ar'CoN(SiMe(3))(2) (2) (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)) are reported. The magnetic data for 2 show that it has an unexpectedly high mu(eff) of 5.65 mu(B) whereas the bent complex 1 has a significantly lower moment.
Chemical Communications 07/2010; 46(25):4466-8. · 6.17 Impact Factor
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Angewandte Chemie International Edition 06/2010; 49(27):4593-7. · 13.45 Impact Factor
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Angewandte Chemie 05/2010; 122(28):4898 - 4900.
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Angewandte Chemie International Edition 05/2010; 49(28):4788-90. · 13.45 Impact Factor
