219958-75-5Relevant articles and documents
A tungsten silyl alkylidyne complex and its bis(alkylidene) tautomer. Their interconversion and an unusual silyl migration in their reaction with dioxygen
Chen, Tianniu,Zhang, Xin-Hao,Wang, Changsheng,Chen, Shujian,Wu, Zhongzhi,Li, Liting,Sorasaenee, Karn R.,Diminnie, Jonathan B.,Pan, Hongjun,Guzei, Ilia A.,Rheingold, Arnold L.,Wu, Yun-Dong,Xue, Zi-Ling
, p. 1214 - 1224 (2008/10/09)
Bis(alkylidene) complex W(=CH-t-Bu)2(CH2-t-Bu)(Si-t- BuPh2) (1a) has been found to be in equilibrium with its alkyl alkylidyne tautomer W(=C-t-Bu)(CH2-t-Bu)2(Si-t-BuPh 2) (1b). Bis(alkylidene) complexes are believed to be intermediates in α-H transfer in alkylidyne complexes W(=CSiMe3)(CH 2-t-Bu)3 and W(=13C-t-Bu)(CH 2-t-Bu)3. The current study represents a rare observation of an exchange between a bis(alkylidene) and an alkyl alkylidyne complex. Thermodynamics and kinetics of the exchange 1a ? 1b have been studied. The equilibrium constant Keq, for the exchange 1a ? 1b is 3.34(0.05) at 287(1) K, and the thermodynamic parameters of the equilibrium measured are ?H° = -3.8(0.8) kJ/mol, ?S° = -3(3) J/mol-K, and ?G°287K = -3(2) kJ/mol. The rate constants k1 and k-1 were obtained from 2D exchange spectroscopy between 267 and 297 K and are 0.34(0.03) and 0.10(0.01) s-1, respectively, at 287 K For the conversion 1a - 1b, activation enthalpy and entropy are ?H? 1 = 75(5) kJ/mol, ?S?1 = 8(25) J/mol-K; for the conversion 1b - 1a, ?H?-1 = 78(5) kJ/ mol, ?S? -1 = 8(25) J/mol-K. In the reaction of 1 with O 2, the silyl ligand in 1b was found to undergo an unprecedented migration to the alkylidyne ligand to give the alkylidene oxo complex W(=O)[=C(t-Bu)(Si-t-BuPh2)](CH2-t-Bu)2 (2). The structure of 2 has been determined. Density functional theory calculations have been conducted for a series of model 1,2-migration reactions. The results suggest that the formation of 2 might be initiated by a 1,2-silyl migration to generate a triplet W-alkylidene intermediate, which is then trapped by O 2.
