Synthesis, Structure, and Silylene Exchange Reaction of Base-Stabilized Hydrido(silylene)tungsten Complexes and Rearrangement of Hydrosilyl(pyridine)tungsten Complexes to the Base-Stabilized Hydrido(silylene) Complexes via 1,2-Hydrogen Migration

Transition Metal Parent Alumylene Complexes: Synthesis, Structures, and XPS Characterization of Aluminum Oxidation State

The first isolation and characterization of transition metal complexes with the parent Al(I)-H unit were achieved in base-stabilized forms. W and Fe complexes, Cp*(CO)n(H)M←:AlH(NHC)2 (NHC = N-heterocyclic carbene, n = 1 or 2), were synthesized in 43-63% yields by the one-step reaction of Cp*M(CO)n(py)Me with H3Al·NHC. The characterization included 1H and 27Al nuclear magnetic resonance (NMR), and infrared (IR) spectroscopic analysis, as well as DFT calculations, which revealed the extremely strong σ-donating ability of the :AlH(NHC)2 ligand, and the highly polarized M(δ-)←:Al(δ+) coordination bonds. The monovalent oxidation state of the Al center of these complexes was confirmed by X-ray photoelectron spectroscopy (XPS). The hydroalumination of carbodiimide and the reduction of CO2 to CO were also demonstrated.

Transition metal chemistry of heavier group 14 congener triple-bonded complexes: syntheses and reactivity

The diversification and synthetic utility of carbyne complexes in organometallic chemistry and catalysis are well recognized, but the syntheses of related heavier group 14 alkylidyne complexes are a recent advancement. A wide range of metal-ylidyne M[triple bond, length as m-dash]E (E = Si-Pb) complexes were synthesized and characterized spectroscopically. The synthetic methodology generally involves elimination or substitution chemistry between metallates and suitable group 14 precursors. The reluctance in forming triple bonded complexes makes this field quite fascinating and challenging. This article gives a brief overview of the pioneering reports followed by detailed information on the latest developments of complexes having a triple bond between a metal and heavier group 14 elements (Si, Ge, Sn, and Pb). Their synthesis and chemistry of the earlier reports followed by recent progress in this field will be discussed. Furthermore, their unique structures and bonding properties will be described based on spectroscopic and theoretical studies.

Silapropargyl/Silaallenyl and Silylene Acetylide Complexes of [Cp(CO)2W]+. Theoretical Study of Their Interesting Bonding Nature and Formation Reaction

The geometry and bonding nature of Cp(CO)(2)W(CCH)(SiH(2)) (1) and the reaction leading to the formation of 1 from Cp(CO)(2)W(SiH(2)C triple bond CH)(9) were theoretically investigated with DFT, MP2 to MP4(SDTQ), and CCSD(T) methods, where 9 and 1 were adopted as models of the interesting new complexes reported recently, Cp*(CO)(2)W(Si(Ph)(2)C triple bond C(t)Bu) and Cp*(CO)(2)W(C triple bond C(t)Bu)(SiPh(2)), respectively. Our computational results clearly indicate that 1 involves neither a pure silacyclopropenyl group nor pure silylene and acetylide groups and that the silylene group strongly interacts with both the W center and the acetylide group. Frontier orbitals of 1 resemble those observed in the formation of silacyclopropene from silylene and acetylene. The frontier orbitals, as well as the geometry, indicate that the (CCH)(SiH(2)) moiety of 1 can be understood in terms of an interesting intermediate species trapped by the W center in that formation reaction. Complex 1 is easily formed from 9 through Si-C sigma-bond activation with moderate activation barriers of 15.3, 18.8, and 15.8 kcal/mol, which are the DFT-, MP4(SDTQ)-, and CCSD(T)-calculated values, respectively. This reaction takes place without a change of the oxidation state of the W center. Intermediate 9 is easily formed from Cp(CO)(2)W(Me)(H(3)SiC triple bond CH) via Si-H oxidative addition, followed by C-H reductive elimination. The bonding nature of 9 is also very interesting; the nonbonding pi-orbital of the H(2)SiCCH moiety is essentially the same as that of the propargyl group, but the pi-conjugation between Si and C atoms is very weak in the pi-orbital, unlike that in the propargyl group.

Group 6 metal complexes with a hemilabile tridentate xantsil ligand and facile insertion of tBuCN into a W–Si bond [xantsil = (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)]

The synthesis and characterization of tungsten and molybdenum complexes of the xanthene-based bis(silyl) ligand (xantsil) with a kappa3(Si,Si,O) coordination mode are reported, where an insertion of tBuCN into a tungsten-silicon bond leads to formation of an eta2-iminoacyl complex.

η:η-Alkynyl-Bridged W−Si Complexes: Formation, Structure, and Reaction with Acetone

Reactions of (eta5-C5Me4R)(CO)2(MeCN)WMe (R = Me, Et) with HPh2SiCCtBu gave the novel alkynyl-bridged W-Si complexes, (eta5-C5Me4R)(CO)2W(mu-eta1:eta2-CCtBu)(SiPh2) (R = Me, Et), whose alkynyl ligands bridge the tungsten and silicon atoms in an eta1:eta2-coordination mode. The structures of these complexes were fully characterized, including X-ray crystallography. Treatment of (eta5-C5Me5)(CO)2W(mu-eta1:eta2-CCtBu)(SiPh2) with acetone resulted in acetone insertion into the silicon-alkynyl linkage followed by intramolecular C-H activation of the tBu group to give the chelate-type alkyl-alkene complex, (eta5-C5Me5)(CO)2W(eta1:eta2-CH2CMe2C=CHSiPh2OCMe2).

Novel eta 3 -1-silaallyl tungsten complexes via Si-H bond activation of hydrovinylsilanes: structure and reactivity toward methanol

Reactions of cis-Cp*(CO)2W(MeCN)Me (1) with HSiMe2(CH=CR2) (R = H, Me) afford the novel eta3-1-silaallyl complexes Cp*(CO)2W(eta3-Me2SiCHCR2) [R = H (2), Me (3)] accompanied by liberation of MeCN and CH4 via thermal Si-H bond activation. eta3-Coordination and exo conformation of the 1-silaallyl ligand in 3 are shown by X-ray crystal analysis, which reveals the partial double bond character of the Si-C bond (1.800(4) A) in the silaallyl moiety. Complexes 2 and 3 show extremely high reactivity toward MeOH to give the hydrido-(methoxysilyl)alkene complex trans-Cp*(CO)2WH(eta2-MeOMe2SiCH=CH2) (4) and the four-membered metallacycle Cp*(CO)2WCH(CHMe2)SiMe2OMe (6), respectively.