Time-resolved IR spectroscopy in liquid rare gases: direct rate measurement of an intermolecular alkane carbon-hydrogen oxidative addition reaction

Abstract

Since the first demonstration of the intermolecular oxidative addition of alkane C-H bonds to transition-metal centers, there have been many studies of the mechanism of this reaction. While these studies have illuminated many aspects of the C-H activation process, they do not provide direct information about the reactive intermediates or the potential energy surface for the elementary insertion reaction. Flash photolysis studies have been thwarted by extremely fast insertion rates in neat alkane solution and by the lack of a suitable inert and transparent solvent for dilution of the alkane. The authors have overcome these difficulties with the use of liquid rare gases as solvents. Using a novel combination of low-temperature and IR laser flash kinetic techniques, we are able to detect the C-H activating transient intermediate formed from Cp*Rh(CO){sub 2} (Cp* = ({eta}{sup 5}-C{sub 5}Me{sub 5})) and measure its rate of reaction with cyclohexane over a wide range of concentrations and temperatures.