Zinc-Promoted ZnMe/ZnPh Exchange in Eight-Coordinate [Ru(PPh 3 ) 2 (ZnMe) 4 H 2 ].

The syntheses, reactivity and electronic structure analyses of [Ru(PPh 3 ) 2 (ZnMe) 4 H 2 ], 1 a, and [Ru(PPh 3 ) 2 (ZnPh) 4 H 2 ], 2 b, are reported. 1 a exhibits an 8-coordinate Ru centre with axial phosphines and a symmetrical (2 : 2) arrangement of ZnMe ligands in the equatorial plane. The ZnMe ligands in 1 a undergo facile, sequential exchange with ZnPh 2 to give 2 b, which shows a 3 : 1 arrangement of ZnPh ligands. Both 1 a and 2 b exist in equilibrium with their respective 3 : 1 and 2 : 2 isomers. Mechanisms for ZnMe/ZnPh exchange and isomerisation are proposed using DFT calculations. The relationships of these {Ru(ZnR) 4 H 2 } species to isoelectronic Group 8 transition metal polyhydrides and related Schlenk equilibria in the Negishi reaction are discussed.