om0341808_si_001.pdf (100.74 kB)
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)
journal contribution
posted on 2004-02-16, 00:00 authored by Paul B. Glaser, Paulus W. Wanandi, T. Don TilleyReaction 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)2OsSiR2][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.