Synthesis, solid-state structure and solution behavior of hydrido-bridged adducts between the group 11 [M(PPh3)]+ cations and the triangular cluster anion [Re3(μ-H)4(CO)9(PPh3)]

The reactions of the unsaturated anion [Re3(μ-H)4(CO)9(PPh3)]- (1) with the metallic Lewis acids [M(PPh3)]+ (M = Cu, Ag, Au) afford the addition derivatives [Re3μ-M(PPh3)(μ3-H)-(μ-H)3(CO)9(PPh3)], which have been characterized in solution and in the solid state, by X-ray analysis. The copper derivative is obtained also by reaction of [Re3(μ-H)3(μs3-H)(CO)9]- (as the [Re(CO)3(Me2CO)3]+ salt) with [Cu(PPh3)2NO3]. Treatment with PPh3 extrudes the [M(PPh3)]+ groups, restoring the starting anion 1. Solid-state structures of the adducts show a butterfly Re3M metal skeleton with one hydride bridging the Re3M face and three hydrides spanning the three Re-Re edges. The interaction of the [M(PPh3)]+ cation with 1 leads only to a minor structural perturbation of the unsaturated Re2(μ-H)2 moiety. The solid-state structure is maintained in nondonor solvents, while in acetone partial (Au, Ag) or complete (Cu) reversible ionic dissociation of the adducts is observed, affording 1 and solvated [M(PPh3)]+ cations. Experiments performed in different solvents show that the donor power and not the dielectric constant is the key factor responsible for dissociation. For the silver adduct the dissociation in acetone is fast on the NMR time scale. The exchange between 1 and the silver or copper (but not gold) adducts occurs even in CD2Cl2.