Synthesis and Structural Comparison of Tp^iPr₂Rh[cis-1,2-bis(diphenylphosphino)ethene]:  Factors Determining Hapticity (κ² vs κ³) of the Tp^iPr₂ Ligand in Tp^iPr₂Rh(diphosphine) Complexes

Comparison of structural and spectroscopic features of the Rh(I)−diphosphine complexes Tp^iPr₂Rh(Ph₂P−X−PPh₂) reveals that the dominant factor governing hapticity of the Tp^iPr₂ ligand (κ² vs κ³) is conformation of the central rhodadiphosphacycle. A folded RhP₂X conformation hinders coordination of the pendant pyrazolyl group due to steric repulsion with the bridging part (X) in diphosphine to lead to a κ²-Tp^iPr₂ species, whereas κ³-coordination is found in complexes with a flat RhP₂X conformation.