Reactivity of (phosphaalkenyl)metal species: Transmetalations and reactions with carbonyl compounds

The (phosphaalkenyl)lithium carbenoid (Z)-Mes*P=CClLi (2; Mes* = supermesityl = 2,4,6-tri-tert-butylphenyl) was transmetalated with MgBr2, ZnCl2, and HgCl2 to furnish the new (phosphavinylidene)metal carbenoids Mes*P=CClMX ((Z)-5a, MX = MgBr; (E)-5b, MX = ZnCl; (E)-5c, MX = HgCl), while with 0.5 equiv of the metal halide, the bis(phosphaalkenyl)metal carbenoids (Mes*P=CCl)(2)M((Z,Z)-6a, M = Mg; (E,E)-6b, M = Zn; (E,E)-6c, M = Hg) were formed. Compounds 2 and 5a were reacted with carbonyl compounds under 1,2-addition, leading to the B-phosphaallyl alcohols 7-10. Bromine-lithium exchange at -90 degrees C between (Z)-Mes*P=CBrSiMe(3) ((Z)-14) and n-butyllithium furnished (E)-/(Z)Mes*P=CLiSiMe(3) ((E)-/(Z)-16; E:Z = 1:1. Transmetalation of (E)-/(Z)-16 with MgBr2 or ZnCl2 furnished only the trans-metal isomer of Mes*P=CMXSiMe(3) ((Z)-18a, MX = MgBr; (E)-18b, MX = ZnCl). From (E)-/(Z)-16, a new access to the phosphaallene Mes*P=C=CPh(2) (20) was obtained by reaction with benzophenone.