Binuclear Carbyne and Ketenyl Derivatives of the Alkyl-Bridged Complexes [Mo2(η5-C5H5)2(μ-CH2R)(μ-PCy2)(CO)2] (R = H, Ph)

The 30-electron benzylidyne complex [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] (Cp = η5-C5H5) could be conveniently prepared upon photolysis of the benzyl-bridged complex [Mo2Cp2(μ-CH2Ph)(μ-PCy2)(CO)2]. It reacted with CO to give the ketenyl complex [Mo2Cp2{μ-C(Ph)CO}(μ-PCy2)(CO)2] (2.6101(2) Å), which in turn could be selectively decarbonylated at 353 K to give the 32-electron benzylidyne derivative [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2] (Mo−Mo = 2.666(1) Å). Related methylidyne complexes could be obtained from the methyl-bridged complex [Mo2Cp2(μ-CH3)(μ-PCy2)(CO)2] via its trinuclear derivative [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)7]. Thus, the carbonylation of the latter cluster gave the ketenyl complex [Mo2Cp2{μ-C(H)CO}(μ-PCy2)(CO)2], whereas its reaction with P(OMe)3 gave the substituted cluster [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)6{P(OMe)3}], which in turn could be thermally degraded to give selectively the 30-electron methylidyne derivative [Mo2Cp2(μ-CH)(μ-PCy2)(μ-CO)] (Mo−Mo = 2.467(1) Å). DFT calculations on the phenylketenyl complex revealed that the metal−ligand interaction is intermediate between the extreme descriptions represented by the acylium (3-electron donor) and ketenyl (1-electron donor) canonical forms of this ligand.