Investigation into the reactivity of M(η5-C5R5)(CO)2(alkane) (M = Mn or Re; R = H, Me or Ph; alkane = n-heptane or cyclopentane) and Re(η5-C5H5)(CO)2(Xe) in solution at cryogenic and room temperature

Abstract

A series of M(η5-C5R5)(CO)2(C5H10) complexes (R = H, Me or Ph; M = Mn or Re) have been characterised at low (Re only) and room temperature (R = H only) using infrared spectroscopy. The decay rates of these complexes have been measured and compared to those of the corresponding n-heptane analogues. These comparisons show that the organometallic cyclopentane complexes are significantly longer-lived than the related n-heptane complexes. The activation parameters for the reaction of the alkane complexes with CO, determined above room temperature, suggest that the reactivity of these complexes is governed by entropic rather than enthalpic factors. The decay rates measured for the permethylated and perphenylated cyclopentadienyl rhenium cyclopentane complexes show that these are more reactive towards CO than Re(η5-C5H5)(CO)2(C5H10). The complex Re(η5-C5H5)(CO)2(Xe) has been characterised in liquid xenon at low temperature, with decay rate studies showing this to have a similar lifetime to Re(η5-C5H5)(CO)2(n-C7H16) in heptane at a similar temperature.