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)(PF3)] 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.