Alkenyl Derivatives of the Unsaturated Dimolybdenum Hydride Complex [Mo2(η5-C5H5)2(μ-H)(μ-PCy2)(CO)2

Abstract

The 30-electron hydride complex [Mo2Cp2(μ-H)(μ-PCy2)(CO)2] reacts at room temperature with p-tolylacetylene to give the unsaturated σ:π-bonded alkenyl derivatives trans-[Mo2Cp2(μ-η1:η2-CRCH2)(μ-PCy2)(CO)2] and trans-[Mo2Cp2(μ-η1:η2-CHCHR)(μ-PCy2)(CO)2] (R = ptol; Cp = η5-C5H5), with the α-substituted alkenyl complex being transformed completely into its β-substituted isomer slowly at room temperature. In solution, both compounds exhibit an isomeric equilibrium (rapid on the NMR time scale) involving the alternate π-binding of the alkenyl ligand to each of the metal centers. In addition, the presence of CO allows the partial conversion of the α-substituted complex into its cis-dicarbonyl isomer cis-[Mo2Cp2(μ-η1:η2-CRCH2)(μ-PCy2)(CO)2], so as to reach a roughly equimolar equilibrium ratio. In contrast, the β-substituted alkenyl complex experiences full carbonylation under the same conditions to give the tricarbonyl complex [Mo2Cp2{μ-η1:η2-CHCHR}(μ-PCy2)(CO)3], but similarly displaying a cisoid arrangement o...