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 MgBr 2, ZnCl 2, and HgCl 2 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 β-phosphaallyl alcohols 7 − 10 . Bromine−lithium exchange at −90 °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 MgBr 2 or ZnCl 2 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.