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-[Mo(1-3-η-HCH2CHCHCH2)(η-C4H 6)(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-C4H 6)(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]BF 4. Reaction of [MoH(η-C5H5)(PMe3)3] with methyl iodide gives [MoH(η-C5H5)(PMe3)2I 2].
