Main Group Chemistry on a Metal Framework: Reactions of - (R=H, CH3) with Lewis Bases

Article abstract of DOI:10.1021/ja00276a026

The reactions of <(μ-H)Fe3(CO)9BH2R>^- (R=H, CH3) with Lewis bases (L=CO, PhMe2P, NEt3, and H2O) are explored.For R=H and L=PhMe2P, substitution via H2 rather than CO elimination to yield <(μ-H)Fe3(CO)8(μ-CO)(PhMe2P)2^-, Fe(CO)3(PhMe2P)2, and a ferroborane anion spectroscopically characterized in situ.The fragmentation pathway predominates in the presence of excess Lewis base, whereas H2 elimination is favored by low ligand levels.For L=PhMe2P the H2 displacement pathway is promoted with R=CH3.A kinetic study for L=PhMe2P reveals a first-order rate dependence on both substrate and ligand for fragmentation, suggesting associative activation.The dual-fragmentation path observed illustrates competitive base displacement of isoglobal fragments from a single cluster.An analysis at intermediate ligand levels results in the definition of base-promoted cluster substitution via H2 elimination.Under the conditions explored here, CO yields only H2 displacement, H2O only fragmentation, and NEt3 adduct formation with slow fragmentation but no H2 displacement.