Stabilization of a Silaaldehyde by its η(2) Coordination to Tungsten.

Treatment of pyridine-stabilized silylene complexes [(η(5)-C5 Me4R)(CO)2(H)W=SiH(py)(Tsi)] (R = Me, Et; py = pyridine; Tsi = C(SiMe3)3) with an N-heterocyclic carbene (Me)I(i)Pr (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) caused deprotonation to afford anionic silylene complexes [(η(5)-C5Me4 R)(CO)2W=SiH(Tsi)][H(Me)I(i)Pr] (R = Me (1-Me); R = Et (1-Et)). Subsequent oxidation of 1-Me and 1-Et with pyridine-N-oxide (1 equiv) gave anionic η(2)-silaaldehydetungsten complexes [(η(5)-C5Me4R)(CO)2W{η(2)-O=SiH(Tsi)}][H(Me)I(i)Pr] (R = Me (2-Me); R = Et (2-Et)). The formation of an unprecedented W-Si-O three-membered ring was confirmed by X-ray crystal structure analysis.