31P chemical shift anisotropies of trimethyl- and triphenylphosphine-substituted Group 6 metal pentacarbonyl complexes

The 31 P chemical shift tensor components and anisotropies of the trimethyl- and triphenylphosphine complexes of the group 6 metal pentacarbonyls, M(CO) 5 PR 3 (M = Cr, Mo, W and R = Me, Ph), have been measured using solid-state CP-MAS 31 P NMR spectroscopy. For the trimethylphosphine derivatives, the chemical shift tensors have near axial symmetry and the shift tensor components are in reasonable agreement with the calculated values for the chromium and molybdenum complexes. In the triphenylphosphine complexes, the tensors are asymmetric due to the different torsion angles of the phenyl rings. The trend to higher shielding of the isotropic 31 P chemical shifts on descending group 6 arises from changes in the perpendicular components of the shift tensor. The one-bond coupling constants, 1 J( 95/97 Mo- 31 P), for the trimethyl- and triphenylphosphine complexes are 129 and 133 Hz, respectively.Key words: chemical shift anisotropy, phosphines, chromium, molybdenum, tungsten.