A delicate balance of complexation vs. activation of alkanes interacting with [Re(Cp)(CO)(PF₃)] studied with NMR and time-resolved IR spectroscopy

The organometallic alkane complexes Re(Cp)(CO)(PF₃)(alkane) and Re(Cp)(CO)₂(alkane) have been detected after the photolysis of Re(Cp)(CO)₂(PF₃) in alkane solvent. NMR and time-resolved IR experiments reveal that the species produced by the interaction of n-pentane with [Re(Cp)(CO)(PF₃)] are an equilibrium mixture of Re(Cp)(CO)(PF₃)(pentane) and Re(Cp)(CO)(PF₃)(pentyl)H. The interaction of cyclopentane with [Re(Cp)(CO)(PF₃)] most likely results in a similar equilibrium between cyclopentyl hydride and cyclopentane complexes. An increasing proportion of alkane complex is observed on going from n-pentane to cyclopentane to cyclohexane, where only a small amount, if any, of the cyclohexyl hydride form is present. In general, when [Re(Cp)(CO)(PF ₃)] reacts with alkanes, the products display a higher degree of oxidative cleavage in comparison with [Re(Cp)(CO)₂], which favors alkane complexation without activation. Species with the formula Re(Cp)(CO)(PF₃)(alkane) have higher thermal stability and lower reactivity toward CO than the analogous Re(Cp)(CO)₂(alkane) complexes.