Organometallic carbonyl substitution kinetics in liquid xenon by fast time-resolved IR spectroscopy

Abstract

The reaction of Cp*Rh(CO)Xe (Cp* = C[sub 5]Me[sub 5]) with CO was studied using time-resolved IR spectroscopy of liquid rare gas solutions. IR spectra for Cp*Rh(CO)Xe were obtained using pulsed UV laser photolysis of Cp*Rh(CO)[sub 2] in liquid Xe and a rapid-scan FTIR spectrometer with 0.09-s time resolution. Assignment to the Xe complex was confirmed from the similarity of the spectra and lifetime of the complex when a mixture of Xe in liquid Kr was used. The reaction of Cp*Rh(CO)Xe with added CO is very fast, and the rate constant was measured by fast time-resolved IR spectroscopy to be (5.7 [+-] 0.6) [times] 10[sup 5] to (1.9 [+-] 0.2) [times] 10[sup 6] M[sup [minus]1] s[sup [minus]1] over the temperature range 202-242 K. The kinetics are consistent with an associative substitution mechanism with activation parameters for the bimolecular rate constant of log(A) = 8.8 [+-] 0.3 ([delta]S* = [minus]20 [+-] 1 cal/(mol K)) and E[sub a] = 2.8 [+-] 0.3 kcal/mol ([delta]H* = 2.4 [+-] 0.3 kcal/mol). 32 refs., 4 figs., 1 tab.