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)(PPh 3 )(PF 3 )(L)] + (dien = diethylenetriamine), where L is an unsaturated organic molecule. The range of ligands which form η 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)(PPh 3 )(PF 3 )} + (dien = diethylenetriamine) displays chemical and spectroscopic characteristics of a potent π-base, it fails to form stable η 2 -coordinated complexes with aromatic molecules. However, its carbonyl analogue {Re(dien)(PPh 3 )(CO)} +, when combined with furan, forms the complex [Re(η 2 -furan)(dien)(PPh 3 )(CO)][OTf], a rare example of a thermally stable η 2 -heterocycle.