Structure and reactivity in complexes of iridium and rhodium. Part I. Crystal and molecular structure of bis-[1,2-bis(diphenylphosphino)ethane]rhodium( I ) perchlorate

Crystals of bis-[1,2-bis(diphenylphosphino)ethane]rhodium(I) perchlorate (monoclinic, space group P21/c, a= 16·264, b= 16·807, c= 21·020 Å, β= 125·29, Z= 4) contain square-planar co-ordinated rhodium with Rh–P 2·306 Å(mean of four) and P–Rh–P (intraligand) 82·7°(mean). The exact conformation adopted in the cation by the bidentate diphosphine ligand, Ph2P·CH2·CH2·PPh2, appears to be determined by non-bonded interactions between the phenyl substituents on the phosphorus atoms. Consideration of the conformations of chelating bidentate diphosphine ligands in this and other structures shows that such ligands are flexible; the feature dominating the structure of these five-membered chelate rings is the staggered conformation about the CH2–CH2 bond. The barriers to torsion about M–P and P–C bonds are apparently lower than about CH2–CH2 bonds.