THE ASYMMETRIC PI-BASES FAC-(RE(DIEN)(PPH3)(PF3))(-(RE(DIEN)(PPH3)(CO))(+) - EVIDENCE FOR FORMATION OF AN ETA(2)-FURAN COMPLEX() AND FAC)

A series of complexes has been prepared of the form [Re(dien)(PPh3)(PF 3)(L)](+) (dien = diethylenetriamine), where L is an unsaturated organ ic molecule. The range of ligands which form eta(2)-coordinate complex es with this metal center includes aldehydes, olefins, and dienes. In addition, thiophene, benzo[b]thiophene, and acetonitrile bind through their heteroatoms. Although {Re(dien)(PPh3)(PF3)}(+) (dien = diethylen etriamine) displays chemical and spectroscopic characteristics of a po tent pi-base, it fails to form stable eta(2)-coordinated complexes wit h aromatic molecules. However, its carbonyl analogue {Re(dien)(PPh3)(C O)}(+), when combined with furan, forms the complex [Re(eta(2)-furan)( dien)(PPh3)(CO)][OTf], a rare example of a thermally stable eta(2)-het erocycle.