The asymmetric π-bases fac-{Re(dien)(PPh3)(PF3)}+ and fac-{Re(dien)(PPh3)(CO)}+:: Evidence for formation of an η2-furan complex

A series of complexes has been prepared of the form [Re(dien)(PPh3)(PF3)(L)](+) (dien = diethylenetriamine), where L is an unsaturated organic molecule. The range of ligands which form eta(2)-coordinate complexes 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 = diethylenetriamine) displays chemical and spectroscopic characteristics of a potent pi-base, it fails to form stable eta(2)-coordinated complexes with aromatic molecules. However, its carbonyl analogue {Re(dien)(PPh3)(CO)}(+), when combined with furan, forms the complex [Re(eta(2)-furan)(dien)(PPh3)(CO)][OTf], a rare example of a thermally stable eta(2)-heterocycle.