Zn-Promoted C-H Reductive Elimination and H Activation via a Dual Unsaturated Heterobimetallic Ru-Zn Intermediate.

Reaction of [Ru(PPh)HCl] with LiCHTMS, MgMe, and ZnMe proceeds with chloride abstraction and alkane elimination to form the bis-cyclometalated derivatives [Ru(PPh)(CHPPh)H][M'] where [M'] = [Li(THF)] (), [MgMe(THF)] (), and [ZnMe] (), respectively. In the presence of 12-crown-4, the reaction with LiCHTMS yields [Ru(PPh)(CHPPh)H][Li(12-crown-4)] (). These four complexes demonstrate increasing interaction between M' and the hydride ligand in the [Ru(PPh)(CHPPh)H] anion following the trend (no interaction) < < < both in the solid-state and solution. Zn species is present as three isomers in solution including square-pyramidal [Ru(PPh)(CHPPh)(ZnMe)] (), that is formed via C-H reductive elimination and features unsaturated Ru and Zn centers and an axial Z-type [ZnMe] ligand. A [ZnMe] adduct of , [Ru(PPh)(CHPPh)(ZnMe)][BAr] () can be trapped and structurally characterized. reacts with H at -40 °C to form [Ru(PPh)(H)(ZnMe)], , and contrasts the analogous reactions of , , and that all require heating to 60 °C. This marked difference in reactivity reflects the ability of Zn to promote a rate-limiting C-H reductive elimination step, and calculations attribute this to a significant stabilization of via Ru → Zn donation. therefore acts as a latent source of and this operational "dual unsaturation" highlights the ability of Zn to promote reductive elimination in these heterobimetallic systems. Calculations also highlight the ability of the heterobimetallic systems to stabilize developing protic character of the transferring hydrogen in the rate-limiting C-H reductive elimination transition states.