Attempted syntheses of ZnPhos-ruthenium complexes (ZnPhos = bis(2-diphenylphosphinophenyl)zinc)

Efforts to prepare Ru-ZnPhos complexes (ZnPhos = bis(2-diphenylphosphinophenyl)zinc) through in situ reactions of the bis-cyclometallated phosphine RuZn₂ complex [Ru(PPh₃)(C₆H₄PPh₂)₂(ZnMe)₂] (1) with the N-Et and N-ⁱPr substituted N-heterocyclic carbenes IEt₂Me₂ (1,3-diethyl-4,5-dimethylimidazol-2-ylidene) and IⁱPr₂Me₂ (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) gave instead the cycloruthenated/cyclozincated bimetallic species [Ru(IEt₂Me₂')(C₆H₄PPh₂)(PPh₂(C₆H₄)Zn{IEt₂Me₂})H] (5; IEt₂Me₂' = cyclometallated IEt₂Me₂) and [Ru(PPh₃)(C₆H₄PPh₂)(PPh(C₆H₄)₂Zn{IⁱPr₂Me₂})H] (7) respectively, both of which feature new Zn-NHC bonds. An alternative approach involving substitution of free ZnPhos into ruthenium monodentate phosphine precursors proved marginally more successful. Heating [Ru(PPh₃)₃(CO)H₂] with excess ZnPhos gave a tetrametallic species 13 comprised of a Ru centre coordinated to ZnPhos and two ZnC₆H₄PPh₂ ligands formed via Zn-C cleavage of two ZnPhos ligands. Substitution into the NHC analogue [Ru(PPh₃)₂(IMe₄)(CO)H₂] (IMe₄ = 1,3,4,5-tetramethylimidazol-2-ylidene) was successful and generated the bridging dihydride complex [Ru(ZnPhos)(IMe₄)(CO)(μ-H)₂] (14).