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

Silanones (OSiR₂) are highly reactive species that readily convert to oligomeric siloxane (O-SiR₂). 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{OSiMes₂(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{OSiMes₂(DMAP)}(SiMe₃) (2a, DMAP: 4-(dimethylamino)pyridine). The SiO 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(OSiMes₂(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.