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.

No abstract

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).

No abstract