Experimental and Theoretical Study of a Tungsten Dihydride Silyl Complex: New Insight into Its Bonding Nature and Fluxional Behavior

Abstract

Tungsten dihydride silyl complex Cp*(CO)2W(H)2[SiH(OMe){C(SiMe3)3}] (R1) was synthesized by the reaction of silylene complex Cp*(CO)2(H)W═Si(H){C(SiMe3)3} (R2) with MeOH. Complex R1 was characterized by spectroscopic data as well as elemental analysis, and its geometry was supported by X-ray crystallography. Interestingly, the variable-temperature 1H NMR spectroscopy revealed that R1 shows highly fluxional behavior, in which two diastereotopic hydrides rapidly exchange their positions in the NMR time scale. The DFT-optimized geometry of Cp(CO)2W(H)2[SiH(OMe){C(SiH3)3}] (1a), which was employed as a model of R1, indicates the presence of a W−silyl and two W−hydride bonds in addition to two weak Si---H interactions. Based on the analyses of molecular orbitals and electron populations, a theoretical understanding of 1a is presented, as follows: (i) 1a is neither a pure dihydride silyl complex of W(IV) bearing d2 electron configuration nor a pure silicate complex of W(II) bearing d4 electron configuration, (i...