Silyl complexes of molybdenum and tungsten - Synthesis, reactivity and structure

The photochemical reaction of Cp2MH2 (M = Mo, 1; W, 2) with several hydridosilanes HSiR3 produces the corresponding silyl hydride complexes Cp2M(H)(SiR3) (M=Mo: SiR3=SiEt3, 3; SiCl3, 4; Si(OEt)(3), 5; SiH2(C5Me5), 6; SiH2(C5Me4H)(2), 7; SiH(C5Me4H)(2), 8; SiH2[2-(Me2NCH2)C6H4], 9; M = W: SiR3=SiCl3, 10) by a reductive elimination/oxidative addition process. Analogous photolysis of 1 in the presence of (C5Me5)(2)SiHCl or (C5Me5)(2)SiH2 does not yield the corresponding complexes Cp2Mo(H)(SiR3) (SiR3=SiCl(C5Me5)(2); SiH(C5Me5)(2)). Treatment of 4 and 6, respectively, with LiAlH4 leads to the hydridosilyl complex Cp2Mo(H)(SiH3) 11. Compounds 6-8 and 11 are expected to be single-source precursors for generation of molybdenum silicides. The hydride complexes 4, 5, and 6 are readily converted to the chloro compounds Cp2Mo(Cl)(SiR3) (SiR3=SiCl3, 12; Si(OEt)(3), 13; SiH2(C5Me5), 14). The reaction of 11 with CCl4 yields complex 12 under exchange of each non-C-bound hydrogen atom. Spectroscopic data of the metallosilanes are discussed and compared with the ones of the parent silanes. An intramolecular N-donor coordination of the functionalized aryl substituent is indicated for 9 by means of Si-29 NMR spectroscopy. 6 undergoes fast sigmatropic rearrangements within the Si-(C5Me5) fragment as proved by a variable temperature H-1 NMR investigation. The structures of 6, 7, 8, and 12 have been determined by single-crystal X-ray diffractometry. Bonding parameters of these typical bent-sandwich complexes are discussed taking account of electronic and steric influences.