Synthesis and structure of a pyridine-stabilized silanone molybdenum complex and its reactions with PMe3 and acetone

Abstract

Silanones (OSiR₂) are highly reactive species that readily convert to oligomeric siloxane (O–SiR₂)_n. The coordination of silanones to transition metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Herein, a pyridine-stabilized silanone molybdenum complex Cp*(OC)₂Mo{OSiMes₂(py)}(SiMe₃) (2b, Cp*: η⁵-C₅Me₅, Mes: 2,4,6-Me₃C₆H₂, and py: pyridine) was synthesized by reacting the silyl(silylene) complex Cp*(OC)₂Mo(SiMes₂)(SiMe₃) (4b) with pyridine-N-oxide in pyridine. X-ray crystal structure analysis revealed that the geometry of complex 2b is similar to those of the previously synthesized DMAP-stabilized analogue Cp*(OC)₂Mo{OSiMes₂(DMAP)}(SiMe₃) (2a, DMAP: 4-(dimethylamino)pyridine). The SiO and Mo–O bond distances in 2b are similar to those observed in 2a, but the N–Si coordination bond of 2b is slightly longer (approximately 0.05 Å) than that of 2a, indicating weaker pyridine coordination than that of DMAP. The reaction of 2a with excess PMe₃ in C₆D₆ at room temperature for 28 h afforded Cp*(OC)₂Mo(PMe₃)(SiMe₃) (5c) in a 43% NMR yield. In contrast, reacting 2b with excess PMe₃ in C₆D₆ at room temperature for 9 h afforded 5c and the five-membered metallacyclic carbene complex Cp*(OC)Mo(C(SiMe₃)OSiMes₂O)(PMe₃) (6) in 10% and 41% NMR yields, respectively. The reactions of pyridine-stabilized silanone complexes Cp*(OC)₂M(OSiMes₂(py))(SiMe₃) (M = Mo (2b) and W (1b)) with acetone proceeded via pyridine elimination, coordination of acetone to the Si center in the silanone ligand, and elimination of HSiMe₃ to give Cp*(OC)₂M{OSiMes₂OC(Me)CH₂} (M = Mo (8) and W (9)) in high yields.