STRUCTURAL-PROPERTIES OF CATIONIC MOLYBDENUM AND TUNGSTEN ALLYL DERIVATIVES

Cationic allyldicarbonyl derivatives of molybdenum and tungsten of the types [M(CO)2(eta-3-allyl)(L3)]PF6 (M = W, allyl = C3H5 or 2-MeC3H4, L3 = bis(2-pyridylmethyl)amine, bpma) and [M(CO)2(eta-3-allyl)(L4)]PF6 (M = Mo or W, allyl = C3H5 or 2-MeC3H4, L4 = tris(2-pyridylmethyl)amine, tpma) have been prepared, and their isomerism and dynamic behaviour in solution examined. In the solid state, [W(CO)2(eta-3-C3H5)(bpma)]PF6 (1a) exhibits an unsymmetric, and [Mo(CO)2(eta-3-C3H5)(tpma)]PF6 (3) a symmetric, orientation of the N-donor set, which comprises two pyridyl rings and the central, exocyclic N of each ligand, with respect to the pi-allyl group. The third bipyridyl ring of tpma in the latter complex is orientated away from the metal centre in the solid, but undergoes rapid exchange with N-donors within the coordination sphere at elevated temperatures in solution. Neither of the 2-MeC3H4 analogues of 3 are dynamic under similar conditions, whereas the 2-MeC3H4 analogue of 1 undergoes a facile trigonal twist rearrangement.