MONOSUBSTITUTED CYCLOPENTADIENYL HALF-SANDWICH TRANSITION-METAL COMPLEXES - LIGAND ORIENTATIONAL EFFECTS

An analysis of crystal structures of the type (eta5-C5H4R)MLx (x = 1-5 ) has been undertaken. A measure of the steric and electronic effects associated with L and R has been assessed from the arrangement of the L ligands relative to R and from the bending of R out of the cyclopent adienyl plane. The analysis revealed that when L and R were large, ste ric effects were dominant and the preferred conformer was such that L and R avoided each other as far as possible. Steric effects for small L and R were significant when x was large. For instance L groups were always staggered with respect to R for x = 4 but for x = 2 both stagge red and eclipsed conformers were observed. Thus electronic factors wer e only dominant for a limited number of structures in which L, R and x were small. The results thus confirm an earlier proposal (N. J. Covil le, K. E. du Plooy and W. Pickl, Coord. Chem. Rev., 116 (1991) 1) that significant steric interactions are anticipated between the ring and the ligand set in (eta5-C5H4R)MLx complexes.