Synthesis and characterization of Group VI metal carbonyl complexes containing closo-1,2-(PPh2)(2)-1,2-C2B10H10 and their conversion to metal carbene complexes

The complexes M(CO)(4)-1,2-(PPh2)(2)-1,2-C2B10H10 (M=Cr 2a, Mo 2b, W 2c) have been prepared in good yields from readily available bis-diphenylphosphino-o-carboranyl ligand, closo-1,2-(PPh2)(2)-(1), 2-C2B10H10 (1), by direct reaction with Group VI metal carbonyls. The infrared spectra of the complexes indicate that there is an octahedral disposition of chelate bis-diphenylphosphino-o-carboranyl ligand around the metal atom. The crystal structure of 2a was determined by X-ray diffraction. Complex 2a crystallizes in the monoclinic space group P 2(1)/n with cell parameters a = 12.2360(7), b = 17.156(1), c = 16.2040(6) Angstrom, V = 3354.1(3) Angstrom(3), and Z = 4. Of the reflections measured a total of 2514 unique reflections with F-2>3 sigma(F-2) was used during subsequent structure refinement. Refinement converged to R-1 = 0.066 and R-2 = 0.071. Structural studies showed that the chromium atom had a slightly distorted pseudo-octahedral configuration about the metal center with two phosphine groups of o-carborane occupying the equatorial plane cis-orientation to each other. These metal carbonyl complexes are rapidly converted to the corresponding metal carbene complexes, [(CO)(3)M=C(OCH3)(CH3)]-1,2-(PPh2)(2)-1,2-C2B10-H-10 (M = Cr 3a, Mo 3b, W 3c), via alkylation with methyllithium followed by O-methylation with CF3SO3CH3.