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)₂OsCH₂SiMe₃ (1, Cp* = C₅Me₅) with an excess of ⁱPr₂Si(H)Cl afforded Cp*(Me₃P)₂OsSiⁱPr₂Cl (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)₂OsSiⁱPr₂OTf (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)₂OsSiMe₂X (X = Cl (4), OTf (5)). Complexes 2−5 were converted to the corresponding base-free silylene complexes [Cp*(Me₃P)₂OsSiR₂][B(C₆F₅)₄] (R = Me (6), ⁱPr (7)) by anion metathesis with Li[B(C₆F₅)₄]·3Et₂O. 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) Å for 6, 2.263(1) Å for 7), and ²⁹Si 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 N₂-bridged diosmium complex [Cp*(Me₃P)₂Os−NN−Os(PMe₃)₂Cp*][B(C₆F₅)₄]₂ (8) and the cyclic siloxane (OSiⁱPr₂)₃. Reaction of 7 with elemental sulfur provided the turquoise, S₂-bridged diosmium complex [Cp*(Me₃P)₂Os−S−S−Os(PMe₃)₂Cp*][B(C₆F₅)₄]₂ (9) and unidentified silicon-containing products.