Synthesis and structure of a pyridine-stabilized silanone molybdenum complex and its reactions with PMe 3 and acetone.

Silanones (OSiR 2 ) are highly reactive species that readily convert to oligomeric siloxane (O-SiR 2 ) 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) 2 Mo{OSiMes 2 (py)}(SiMe 3 ) (2b, Cp*: η 5 -C 5 Me 5 , Mes: 2,4,6-Me 3 C 6 H 2 , and py: pyridine) was synthesized by reacting the silyl(silylene) complex Cp*(OC) 2 Mo(SiMes 2 )(SiMe 3 ) (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) 2 Mo{OSiMes 2 (DMAP)}(SiMe 3 ) (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 PMe 3 in C 6 D 6 at room temperature for 28 h afforded Cp*(OC) 2 Mo(PMe 3 )(SiMe 3 ) (5c) in a 43% NMR yield. In contrast, reacting 2b with excess PMe 3 in C 6 D 6 at room temperature for 9 h afforded 5c and the five-membered metallacyclic carbene complex Cp*(OC)Mo(C(SiMe 3 )OSiMes 2 O)(PMe 3 ) (6) in 10% and 41% NMR yields, respectively. The reactions of pyridine-stabilized silanone complexes Cp*(OC) 2 M(OSiMes 2 (py))(SiMe 3 ) (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 HSiMe 3 to give Cp*(OC) 2 M{OSiMes 2 OC(Me)CH 2 } (M = Mo (8) and W (9)) in high yields.