Transforming PPh3 into Bidentate Phosphine Ligands at Ru-Zn Heterobimetallic Complexes

The reaction of [Ru(PPh ₃) ₃Cl ₂] with excess ZnMe ₂ led to P-C/C-H bond activation and P-C/C-C bond formation to generate a chelating diphenylphosphinobenzene ligand as well as a cyclometallated (diphenylphosphino)biphenyl group in the final product of the reaction, [Ru(dppbz)(PPh ₂(biphenyl)′)(ZnMe)] (1; dppbz = 1,2-bis(diphenylphosphino)benzene); PPh ₂(biphenyl)′ = cyclometallated PPh ₂(biphenyl). The mechanism of reaction was studied and C-C coupling to give a bidentate 2,2′-bis(diphenylphosphino)biphenyl (BIPHEP) ligand was suggested to be one of the key steps of the process. This was confirmed by the reaction of [Ru(BIPHEP)(PPh ₃)HCl] with ZnMe ₂, which also gave 1. An analogous set of steps took place upon addition of ZnMe ₂ to [Ru(rac-BINAP)(PPh ₃)HCl] (rac-BINAP = racemic(2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) to give [Ru(dppbz)(PPh ₂(binaphthyl)′)ZnMe] (3). H ₂ and the C-H bond of PhCCH added across the Ru-Zn bond of 1, and also reversed the phosphine cyclometallation, to give [Ru(dppbz)(Ph ₂P(biphenyl))(H) ₂(H)(ZnMe)] (4) and [Ru(dppbz)(Ph ₂P(biphenyl))(CCPh) ₂(H)(ZnMe)] (5) respectively.