C-(Halide) Oxidative Addition Routes to Ruthenium Carbenes

Ru(H)(2)(H(2))(2)L(2) (L = PCy(3)) reacts with CHRCl(2) (R = H, Ph) to give Ru(CHR)Cl(2)L(2) and H(2). Using Cl(2)C=CH(2) as the gem-dihalide gives Ru(CHCH(3))Cl(2)L(2), due to hydrogenation of the C=C bond of the presumed vinylidene primary product by released H(2). Released H(2) also reacts with Ru(CHR)Cl(2)L(2) (R = H, Ph) to give H(3)CR, HCl and RuHCl(H(2))L(2). This undesirability of H(2) as a coproduct can be diminished by using Ru(H)(2)(N(2))(2)L(2) as the reagent, giving Ru(CHR)Cl(2)L(2) and 1H(2) and 2N(2) as products. Reaction of Ru(H)(2)(N(2))(2)L(2) with Cl(2)CHEt gives RuCl(2)(CHEt)L(2) and RuHCl(N(2))L(2), the latter apparently by competitive beta-H migration from an intermediate RuHCl(CHClEt)L(2) species. When Ru(H)(2)(N(2))(2)L(2) is reacted with the monochloride PhCH(2)Cl, the primary product RuCl(CH(2)Ph)(H(2))L(2) slowly (hours) evolves further to give RuHCl(N(2))L(2) and PhCH(3). Reaction of Ru(H)(2)(N(2))(2)L(2) with C(6)F(6), BrHC=CHPh, and CH(3)I give RuHX(N(2))L(2) (X = F, Br, I, respectively). The N(2) ligand in RuHCl(N(2))L(2) can be displaced by H(2) and by CO, while H(2) converts RuHF(N(2))L(2) to Ru(H)(2)(H(2))(2)L(2) and HF.