Hexakis(trimethylphosphine)molybdenum chemistry: dinitrogen, ethylene, butadiene, η-cyclopentadienyl, and related derivatives

Abstract

Co-condensation of molybdenum atoms with trimethylphosphine gives octahedral [ Mo(PMe₃)₆](1) whose crystal structure has been determined. Treatment of (1) with dinitrogen, ethylene, carbon monoxide, iodine, or butadiene gives [Mo(N₂)(PMe₃)₅], trans-[Mo(η-C₂H₄)₂(PMe₃)₄]fac-[Mo(CO)₃(PMe₃)₃], trans-[MoI₂(PMe₃)₄], and cis-[Mo(η-C₄H₆)₂(PMe₃)₂] respectively. Protonation of cis-[Mo(η-C₄H₆)₂(PMe₃)₂] with tetrafluoroboric acid forms the compound cis-[[graphic omitted]CH₂CHCHCH₂)(η-C₄H₆)(PMe₃)₂]BF₄. The presence of the Mo–H–C bond is shown by low-temperature n.m.r. spectra, and variable-temperature n.m.r. shows that the agostic hydrogen can scramble between the four terminal carbons of the two C₄ ligands. The rate constants and activation parameters for the hydrogen-scrambling process have been determined and a mechanism is proposed. Reaction of cis-[Mo(η-C₄H₆)₂(PMe₃)₂] with trifluoroacetic acid gives [Mo(η-MeC₃H₄)(η-C₄H₆)(PMe₃)₂(O₂CCF₃)]. Treatment of [Mo(PMe₃)₆] with cyclopentadiene forms [MoH(η-C₅H₅)(PMe₃)₃] which reacts with aqueous tetrafluoroboric acid giving [MoH₂(η-C₅H₅)(PMe₃)₃]BF₄ and [Mo(η-C₅H₅)(PMe₃)₂O]BF₄. Reaction of [MoH(η-C₅H₅)(PMe₃)₃] with methyl iodide gives [MoH(η-C₅H₅)(PMe₃)₂I₂].