Syntheses and structures of methyltris(pyrazolyl)silane complexes of the group 6 metals

The methyltris(3,5-dimethylpyrazolyl)silane ligand, Tps(Me2), was readily p repared by the metathesis reaction of methyltrichlorosilane with 3 equiv of lithium 3,5-dimethylpyrazolate. The octahedral tricarbonyl complexes (Tps( Me2))M(CO)(3) were synthesized either by ligand exchange with the labile ni trile adducts M(CO)(3)(NCR)(3) (M = Cr, Mo, R = Me; M = W, R = Et) or therm ally by direct substitution on the hexacarbonyls M(CO)(6) (M = Cr, Mo). The three new complexes were characterized by a combination of analytical and spectroscopic techniques, including electrospray ionization mass spectromet ry and single-crystal X-ray diffraction. They are all isostructural and dis play in the solid state the expected distorted octahedral geometries with f acially coordinated tris(pyrazolyl)silane ligands. Crystallographic data we re used to calculate the ligand cone angles (251-264 degrees) in (Tps(Me2)) M(CO)(3) and also to estimate a value of 1.59 Angstrom for the covalent rad ius of octahedral W(0).