Reactivity of cationic molybdenum(II) complexes. Part 1. Hydride reduction of the 18 electron complexes [Mo(CO)3(η-C5Me5)L]+[L = PPh3 or P(OMe)3] and isolation of the thermally stable formyl complex cis-[Mo(CO)2(η-C5Me5){P(OMe)3}(CHO)]. Crystal structure of [Mo(CO)3(η-C5Me5)(PPh3)]BF4·0.5MeOH

Abstract

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.