Synthesis and reactivity of d(0) bis(imido) silyl and germyl complexes of molybdenum and tungsten

The syntheses and reactivities of d(0) bis(imido) molybdenum/tungsten silyl chloride complexes (2,6-(Pr2C6H3N)-Pr-i)(2)M[Si(SiMe3)(3)]Cl (1, M = MO; 2, M = W) and the corresponding germyl complexes (2,6-(Pr2C6H3N)-Pr-i)(2)M[Ge(SiMe3)(3)]Cl (3, M = Mo; 4, M = W) are described. The complex (2,6-(Pr2C6H3N)-Pr-i)(2)Mo[Si(SiMe3)(3)]Cl (1), prepared by the reaction of (2,6-(Pr2C6H3N)-Pr-i)(2)MoCl2(dme) with (THF)(3)LiSi(SiMe3)(3), has been structurally characterized. In general, these complexes are rather stable and do not react with CO, Hz, or CH3CN. Complex 1 reacts with 2,6-Me2C6H3NC to provide the insertion product (2,6-(Pr2C6H3N)-Pr-i)(2)Mo[eta(2)-C(N-2,6-Me2C6H3)Si(SiMe3)(3)](Cl) (5) and with AgOTf to give the silyl triflate complex (2,6(i)Pr(2)C(6)H(3)N)(2)Mo[Si(SiMe3)(3)]OSO2CF3 (6) in high yield. Complexes 1-6 react with neopentylmagnesium chloride to produce the silyl neopentyl complexes (2,6-(Pr2C6H3N)-Pr-i)(2)M[E(SiMe3)(3)](CH2CMe3) (7, M = Mo, E = Si; 8, M = W, E = Si; 9, M = Mo, E = Ge; 10, M = W, E = Ge). Complex 7, which was characterized by X-ray crystallography, contains an agostic interaction involving the cr hydrogen of the neopentyl ligand (d(Mo-H) 2.55(4)Angstrom). The neopentyl complexes 7-10 readily react with hydrogen (1 atm) to generate free neopentane and HSiMe3, probably via hydrogenation of the Mo-C bond to generate a highly unstable silyl hydride intermediate. The mechanism of HSiMe3 formation is unknown but may involve decomposition of the silyl hydride species via a four-membered transition state to generate a highly reactive silylene species. The corresponding tungsten analog 8 undergoes a similar reaction, but at a much slower rate. Attempts to trap the possible silylene intermediates (2,6-(Pr2C6H3N)-Pr-i)(2)M=Si(SiMe3)(2) (M = Mo, W) were unsuccessful.