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.
Ray
Mausumi
M
Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
Nakao
Yoshihide
Y
Sato
Hirofumi
H
Sakaba
Hiroyuki
H
Sakaki
Shigeyoshi
S