Reactivity of Cationic Molybdenum(II) Complexes. Part 1. Hydride Reduction of the 18 Electron Complexes [Mo(CO)3(eta-C5Me5)] + [L=PPh3 or P(OMe)3] and Isolation of the Thermally Stable Formil Complex cis-[Mo(CO)2(eta-C5Me5){P(OMe)3}(CHO)] Crystal Structure of [Mo(CO)(eta-C5Me5)(PPh3)]BF4.0.5MeOH

The compound [Mo(CO)3(η-C5Me5)]BF4 reacts with π acids, L [L = PPh3, P(OMe)3, CO, or p-MeC6H4NC], giving the 18 electron cations [Mo(CO)3(η-C5Me5)L]+. The complex [Mo(CO)3(η-C5Me5)(PPh3)]BF4 (1) has been characterized by a single-crystal X-ray diffraction study. The reaction of (1) with one equivalent of Na[BH4] gives the neutral metal formyl complex [Mo(CO)2(η-C5Me5)(PPh3)(CHO)], (2), which, in solution, converts to [MoH(CO)3(η-C5Me5)] above –40 °C. If [Mo(CO)3(η-C5Me5){P(OMe)3}]BF4, (3), is used instead of (1), the reduction in methanol solution with Na[BH4] allows isolation of the thermally stable cis-[Mo(CO)2(η-C5Me5){P(OMe)3}(CHO)], (4). Thermal decomposition of (4) in methanol solution at room temperature is slow and gives cis-[MoH(CO)2(η-C5Me5){P(OMe)3}]. This result emphasizes that the great difference observed in the thermal stability of complexes (2) and (4) is attributable to different decomposition pathways.