PHOTOOXIDATION OF THE MOLYBDENUM AND TUNGSTEN CARBYNES (ETA-5-C5H5)L2M=CR [L = P(OME)3, CO AND R = PH, ME, C-C3H5]

Photolysis of the carbyne complexes CpL1L2M = CR, 3a-d and 4a,b (M = Mo, W; L1 = P(OMe)3; L2 = CO, P(OMe)3; R = Ph, Me, c-C3H5), in chlorinated solvents in the presence of PMe3 results in the formation of the cationic complexes [Cp(Cl)(PMe3)2M = CR]+Cl- (5a-d). All of the carbyne complexes were spectroscopically characterized. The formation of 5a-d is postulated to involve electron transfer from the MLCT excited states of the carbynes to the chlorinated solvent. The resulting 17e- species then undergo ligand exchange followed by halogen atom abstraction to afford the observed cationic complexes. UV-visible spectroscopy of 3a-d and 4a,b has established that electron transfer occurs upon MLCT excitation rather than from CTTS transitions, while EHMO calculations on the model system Cp[P(OH)3]2Mo = CPh are in agreement with the MLCT band being d - pi* in nature. For the cases L1 = P(OMe)3, L2 = CO, R = Ph or tolyl, the MLCT state was also responsible for emission in fluid solution at room temperature. The carbyne Cp(CO)[P(OMe)3]W = C(o-Tol) (3e) was characterized by X-ray crystallography: monoclinic, C2/c, a = 32.754 (10) angstrom, b = 7.294 (3) angstrom, c = 15.521 (7) angstrom, beta = 98.982 (5)degrees, V = 3662.5 (5) angstrom3, Z = 8, R(F) = 5.0%, R(wF) = 5.6% for 1692 reflections, F(o) greater-than-or-equal-to 3-sigma(F(o)).