Reversible Opening of the Triangular Structure of a Sulfido-Bridged ZrRh₂ Early−Late Heterobimetallic Complex Induced by Bis-(diphenylphosphino)methane

Reaction of the early−late heterobimetallic complexes [Cp^tt₂Zr(μ₃-S)₂{M(CO)}₂(μ-dppm)] (M = Rh, Ir) with dppm (bis-(diphenylphosphino)methane) yields the compounds [Cp^tt₂Zr(μ-S)₂M(μ-CO)₂(μ-dppm)M(η²-dppm)] (M = Rh (3), Ir (4)). The molecular structure of 3 shows a bent trimetallic ZrRhRh chain with tetrahedral, trigonal-bipyramidal, and square-pyramidal geometries, respectively. This trinuclear compound exhibits a mixed-valence Rh(II)−Rh(0) metal−metal bonded unit that results from the unusual chelating coordination of the metalloligand [Cp^tt₂Zr(S)₂]^2- and is further stabilized by the presence of two unsymmetrical bridging carbonyl ligands, which interact with the unsaturated Rh(II) metal. The formation of 3 is reversible, and the equilibrium 1 + dppm 3 has been observed in solution (K ≈ 16 at 22 °C in C₆D₆). The opening of the triangular core in the heterotrimetallic compound [Cp^tt₂Zr(μ₃-S)₂{Rh(CO)}{Ir(CO)}(μ-dppm)] (5) is not selective and gives the compounds [Cp^tt₂Zr(μ-S)₂Rh(μ-CO)₂(μ-dppm)Ir(η²-dppm)] (6) and [Cp^tt₂Zr(μ-S)₂Ir(μ-CO)₂(μ-dppm)Rh(η²-dppm)] (7) in a 3:1 molar ratio.