BH bond activation of trimethylphosphineborane by transition metal complexes: Synthesis of metal complexes bearing nonsubstituted boryl-trimethylphosphine, Cp*M(CO)(3)(BH2 center dot PMe3) (M = Mo, W)

Photolysis of methylmolybdenum and tungsten complexes, Cp*M(CO)(3)Me (M = M o, W), in the presence of BH3.PMe3 (1) afforded nonsubstituted boryl comple xes Cp*M(CO)(3)(BH2.PMe3) (2a: M = Mo, 3a: M = W) with concomitant evolutio n of methane. The structures of 2a and 3a were determined by single-crystal X-ray crystallography. The boryl group in these complexes adopts a tetra-c oordinate geometry with coordination of trimethylphosphine to the boron ato m. The tungsten-boron bond distance in 3a is significantly longer than thos e of boryltungsten complexes with a tri-coordinate boryl group. The CO stre tching bands in the IR spectra of 2a and 3a were observed at lower wavenumb ers than those of the corresponding methyl complexes, indicating the pronou nced polarization of the M-B bond, M(-)-B(+). Reactivity of the boryl compl exes also featured the polar M-B bond. Boryl complexes having a nonsubstitu ted cyclopentadienyl ligand, CpM(CO)(3)(BH2.PMe3) (2b: M = Mo, 3b: M = W) w ere generated by the similar photoreaction although they were thermally uns table.