Synthesis, structure, and reactivity of a pyridine-stabilized silanonetungsten complex.

Abstract

A pyridine-stabilized silanonetungsten complex Cp*(OC)2W{O[double bond, length as m-dash]SiMes2(py)}(SiMe3) (1b, Cp* = η5-C5Me5, Mes = 2,4,6-Me3C6H2, py = C5H5N) was obtained by the reaction of a silyl(silylene) complex Cp*(OC)2W([double bond, length as m-dash]SiMes2)(SiMe3) (3) with pyridine-N-oxide in pyridine. X-ray crystal structure determination revealed that complex 1b shows a similar geometry to that observed for a previously synthesized DMAP-stabilized analogue, Cp*(OC)2W{O[double bond, length as m-dash]SiMes2(DMAP)}(SiMe3) (1a, DMAP = 4-NMe2C6H4N). The Si[double bond, length as m-dash]O and W-O bond distances in 1b are comparable to those observed in 1a, but the nitrogen to silicon coordination bond of 1b is slightly longer (ca. 0.05 Å) than that of 1a, indicating the weaker coordination of pyridine than that of DMAP. The reaction of 1b with excess PMe3 in C6D6 at r. t. proceeded via elimination of pyridine to afford a five-membered metallacyclic carbene complex, Cp*(OC)W([double bond, length as m-dash]C(SiMe3)OSiMes2O)(PMe3) (5), but that of 1a with PMe3 did not proceed at all. Complex 5 was further transformed in C7D8 at 100 °C for 4 h to give a four-membered W-O-Si-O metallacyclic complex with carbyne and PMe3 ligands, Cp*W(OSiMes2O)([triple bond, length as m-dash]CSiMe3)(PMe3) (7). The structural features of complexes 1b, 5, and 7 are comparable to those suggested theoretically as intermediates in the reaction of 3 with a sulfuration reagent to afford a six-membered metallacyclic carbene complex, Cp*W(S){[double bond, length as m-dash]C(SiMe3)C([double bond, length as m-dash]O)OSiMes2S} (6), indicating that complex 1b and the theoretically proposed silanethione complex are transformed via a similar reaction pathway.