Mono- and binuclear quinaldinate complexes of rhodium with (PP) donor ligands. Crystal structure of [Rh 2(quin) 2(CO) 2(μ-dppm)]. Oxidative addition reactionsV

Abstract

Reactions of [Rh(quin)(CO) 2] (quin = 2-quinaldinate, C 9H 6N-COO − with diphosphine ligands [dppm (bis(diphenylphosphino)methane) or dppe ([1,2-bis(diphenylphosphino)ethane)] gave two types of compound, [Rh 2(quin) 2(CO) 2(μ-PP)] and [Rh(quin)(PP)] (PP = dppm, dppe) depending on the Rh: PP molar ratio employed. 2:1 or 1:1, respectively. The binuclear [Rh 2(quin) 2(CO) 2(μPP)] species present a square-planar environment for each rhodium atom, which are bonded by a PP bridging ligand. These results were also proved by the resolution of the crystal structure of [Rh 2(quin) 2 (CO) 2(μ-dppm)]. The molecular structure shows the two CO groups occupying trans positions. This could prevent the formation of possible binuclear CO-free species. The RhRh intramolecular distance was consistent with no formal RhRh bond. The addition of I 2 or CH 3I to the above [Rh 2(quin) 2(CO) 2(μ-PP)] gave rise to the corresponding binuclear hexacoordinate rhodium(III) compounds [Rh 2(I) 2(X) 2(quin) 2(CO) 2(μ-PP)] (X = I, CH 3). Two isomers were detected in solution by 1H and 31P NMR spectroscopy for [Rh 2(I) 2(CH 3) 2(quin) 2(CO) 2(μ-PP)].