DIBROMOALKYNE COMPLEXES OF TUNGSTEN(II)

Treatment of [WBr2(CO)(3)(NCMe)(2)] with an excess of MeC(2)Me or two equivalents of RC(2)R (R = Ph or CH2Cl) in CH2Cl2 at room temperature gave the bis(alkyne) complexes [WBr2(CO)(NCMe)(eta(2)-RC(2)R)(2)]. Two equivalents of PPh(2)Cy reacts with [WBr2(CO)(NCMe)(eta(2)-MeC(2)Me)( 2)] to afford the bis(phosphine complex [WBr2(CO)(PPh(2)Cy)(2)(eta(2)- MeC(2)Me)]. Equimolar quantities of [WBr2(CO)(NCMe)(eta(2)-MeC(2)Me)(2 )] and L Lambda L [L Lambda L = Ph(2)P(CH2)(n)PPh(2) (n = 1-6) or 2,2' -bipy] react in CH2Cl2 at room temperature to give either [WBr2(CO){Ph (2)P(CH2)(n)PPh(2)}(eta(2)-MeC(2)Me)] or [WBr(CO)(2,2'bipy) (eta(2)-Me C(2)Me)2]Br, respectively. The cationic nature of [WBr(CO)(2,2'-bipy)( eta(2)-MeC(2)Me)(2)]Br was confirmed by reaction with Na[BPh(4)] in ac etonitrile to give [WBr(CO)2,2'-bipy)(eta(2)-MeC(2)Me)(2)][BPh(4)]. Th e barrier to but-2-yne rotation of selected mono(but-2-yne) complexes was determined by using variable temperature H-1 NMR spectroscopy. C-1 3 NMR spectroscopy was used to suggest the number of electrons donated to the metal for selected complexes.