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.

The dinuclear polyhydride [Cp*RuH 2 ] 2 (Cp* ) C 5 Me 5 ) reacts with thiophene at ambient temperature to give a C-S ring-opened "flyover" complex in which all atoms are bound to the metal centers. A similar reaction with 2-methylthiophene also gives a related product. The products were characterized by singlecrystal X-ray diffraction.