REACTIONS OF THE TRIOSMIUM COMPLEX OS3(CO)10(MU-BR)(CH=CHPH) WITH BENZYL ISONITRILE AND TRIPHENYLPHOSPHINE - CRYSTAL-STRUCTURE AND SOLUTION FLUXIONALITY OF THE ETHENYL DERIVATIVES

Reaction of Os3(CO)10(mu-Br)(CH = CHPh) (1) with benzyl isonitrile in toluene at 85-degrees-C gave a trinuclear complex Os3(CO)9(CNCH2Ph) (mu-Br)(CH = CHPh) (2). In contrast, the analogous reaction with triphenylphosphine at 110-degrees-C produced dinuclear complexes Os2(CO)5(PPh3)(mu-Br)(CH = CHPh) (4). The ethenyl group of complex 2 is static; however, variable temperature NMR studies indicate that the ethenyl groups of 3 and 4 undergo rapid pi --> sigma, sigma --> pi rearrangement (reversible flipping of the vinyl group) in solution. The structures of 2 and 3 were also determined by single-crystal X-ray diffraction. Crystal data for 2: space group P2(1)/c; a = 9.977(2), b = 22.779(6), c = 25.323(5) angstrom, beta = 95.08(2)-degrees, Z = 8; final R = 0.038, R(w) = 0.037 for 3445 reflections with I greater-than-or-equal-to 3-sigma(I). Crystal data for 3: space group P1BAR; a = 10.749(2), b = 13.101(3), c = 13.208(3) angstrom, alpha = 118.73(2), beta = 105.4992), gamma = 97.62(2)-degrees; Z = 2; final R = 0.027, R(w) = 0.026 for 4211 reflections with I > 2-sigma(I).