Synthesis, structure, and reactivity of osmium silyl and silylene complexes Cp*(Me3P)2OsSiR2X and [Cp*(Me3P)2OsSiR2][B(C6F5)4] (R = Me, iPr; X = Cl, OTf)

Reaction of Cp*(Me3P)(2)OsCH2SiMe3 (1, CP* = C5Me5) with an excess of (Pr2Si)-Pr-i(H)Cl afforded Cp*(Me3P)(2)(OsSiPr2Cl)-Pr-i (2) in good yield, without the formation of Os(IV) products. Treatment of 2 with Me3SiOTf (OTf = triflate, OSO2CF3) afforded the corresponding triflatosilyl complex Cp*(Me3P)(2)(OsSiPr2OTf)-Pr-i (3), which appears to possess substantial silylene character, as determined by structural and spectroscopic measurements. The synthetic route to these complexes is analogous to that employed for the previously reported dimethylsilyl compounds Cp*(Me3P)(2)OsSiMe2X (X = Cl (4), OTf (5)). Complexes 2-5 were converted to the corresponding base-free silylene complexes [Cp*(Me3P)(2)Os=SiR2] [B(C6F5)(4)] (R = Me (6), Pr-i (7)) by anion metathesis with Li[B(C6F5)(4)](.)3Et(2)O. Both 6 and 7 were characterized by. multinuclear NMR spectroscopy and X-ray crystallography. The silylene complexes feature a trigonal planar environment for silicon, short Os-Si contacts (2.257(7) Angstrom for 6, 2.263(1) Angstrom for 7), and Si-29 NMR resonances that are shifted to very low field (350 ppm for 6; 363 ppm for 7). The spectroscopic and structural differences between these silylene complexes and their precursors are discussed. While stable in fluorobenzene, 6 and 7 are rapidly oxidized by chlorocarbons via a radical pathway to form cationic Os(III) chlorosilyl species. Reactions of 7 with oxygen atom sources such as N2O and 2-picoline N-oxide afforded the N-2-bridged diosmium complex [Cp*(Me3P)(2)Os-NN-Os(PMe3)(2)CP*][B(C6F5)(4)](2) (8) and the cyclic siloxane ((OSiPr2)-Pr-i)(3). Reaction of 7 with elemental sulfur provided the turquoise, S-2-bridged diosmium complex [Cp*(Me3P)(2)Os-S-S-Os(PMe3)(2)CP*] [B(C6F5)(4)](2) (9) and unidentified silicon-containing products.