Flash infrared kinetics of the photochemistry of Tp*Rh(CO)(2) and Bp*Rh(CO)(2) in liquid xenon solution

The photochemistry of Tp*Rh(CO)(2) (1; Tp* = hydridotris(3,5-dimethylpyrazo lyl)borate) in liquid xenon solution at -50 degrees C has been examined by flash IR kinetic spectroscopy. IR spectra of the solution taken 2 mu s afte r 308 nm photolysis exhibit two transient bands at 1976-1980 and. 1994-1998 cm(-1), respectively, both of which decay with the same first-order rate c onstant (k = 2 x 10(4) s(-1)). In the presence of excess CO, the rates of d ecay of both of these bands increase by an order of magnitude and correlate with the rate of recovery of the CO stretch of the parent complex. Photoly sis of xenon solutions of Bp*Rh(CO)(2) (5; Bp* = dihydridobis(3,5-dimethylp yrazolyl)borate) produces a transient species with a single IR absorption a t 1996-2000 cm(-1). Upon addition of pyridine to the solution, this transie nt photoproduct reacts to form the new, stable complex Bp*Rh(CO)(pyridine), with an IR absorption at 1978 cm(-1). On the basis of these results, the 1 978 and 1996 cm(-1) bands observed upon photolysis of 1 are attributed to t he solvates (eta(3)-Tp*)Rh(CO).Xe and (eta(2)-Tp*)Rh(CO). Xe (2 Xe and 3 Xe , respectively). Preliminary kinetic data for the reaction of 1 with cycloh exane in xenon solution indicate that both the 1978 and 1996 cm(-1) transie nt bands still appear and that their rates of decay correlate with formatio n of the Ph alkyl hydride product Tp*Rh(CO)(cyclohexyl)(H) (4), absorbing a t 2032 cm(-1).