Preparation and crystal and molecular structure of (η3-octamethylcyclotetraphosphazane-P,P,P)tricarbonylmolybdenum(0), [η3-(CH3PNCH3)4]Mo(CO)3

Abstract

The synthesis and physical properties of the phosphazane complex [η3-(CH3PNCH3)4]Mo(CO)3 are reported. Crystals of (η3-octamethylcyclotetraphosphazane-P,P,P)tricarbonylmolybdenum(0) are monoclinic, a = 8.6898(9), b = 16.0987(8), c = 14.1156(17) Å, β = 98.321(6)°, Z = 4, space group Cc. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to R = 0.020 and Rw = 0.024 for 2286 reflections with I ≥ 3σ(I). The molybdenum atom is coordinated to three phosphorus atoms of the (MePNMe)4 ligand and to three carbonyl ligands in a distorted octahedral geometry. The molecule has approximate mirror symmetry in the solid state. Important bond lengths (corrected for libration) are: Mo—P = 2.537(1), 2.467(1), and 2.513(1), Mo—C = 1.971(4), 2.002(4), and 1.978(4), mean P—N = 1.704(8) for coordinated P, 1.735(7) Å for uncoordinated P. The structural evidence indicates that the phosphazane is a weaker donor to Mo(CO)3 than to three sulphur atoms, and that coordination withdraws electron density from the fourth phosphorus atom. The complex is fluxional in solution.