Synthesis and Reactivity of d⁰Bis(imido) Silyl and Germyl Complexes of Molybdenum and Tungsten

The syntheses and reactivities of d0 bis(imido) molybdenum/tungsten silyl chloride complexes (2,6-iPr2C6H3N)2M[Si(SiMe3)3]Cl (1, M = Mo; 2, M = W) and the corresponding germyl complexes (2,6-iPr2C6H3N)2M[Ge(SiMe3)3]Cl (3, M = Mo; 4, M = W) are described. The complex (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3]Cl (1), prepared by the reaction of (2,6-iPr2C6H3N)2MoCl2(dme) with (THF)3LiSi(SiMe3)3, has been structurally characterized. In general, these complexes are rather stable and do not react with CO, H2, or CH3CN. Complex 1 reacts with 2,6-Me2C6H3NC to provide the insertion product (2,6-iPr2C6H3N)2Mo[η2-C(N-2,6-Me2C6H3)Si(SiMe3)3](Cl) (5) and with AgOTf to give the silyl triflate complex (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3]OSO2CF3 (6) in high yield. Complexes 1−6 react with neopentylmagnesium chloride to produce the silyl neopentyl complexes (2,6-iPr2C6H3N)2M[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 α hydrogen of the neopentyl ligand (d(Mo−H) 2.55(4)Å). 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-iPr2C6H3N)2MSi(SiMe3)2 (M = Mo, W) were unsuccessful.