Synthesis and Structural Comparison of TpiPr2Rh[cis-1,2-bis(diphenylphosphino)ethene]:  Factors Determining Hapticity (κ2 vs κ3) of the TpiPr2 Ligand in TpiPr2Rh(diphosphine) Complexes

Comparison of structural and spectroscopic features of the Rh(I)−diphosphine complexes TpiPr2Rh(Ph2P−X−PPh2) reveals that the dominant factor governing hapticity of the TpiPr2 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-TpiPr2 species, whereas κ3-coordination is found in complexes with a flat RhP2X conformation.