Reaction intermediates in organometallic chemistry studied by time-resolved infrared spectral techniques

Abstract

Applications of flash photolysis with time resolved infrared (TRIR) detection techniques to kinetics investigations of reactive organometallic intermediates are described. The apparatus used a XeCl excimer laser as the pump source and lead salt diode lasers as probe sources with an overall tuning range from 1550 to 2200 cm1. For illustration, flash photolysis studies of some ruthenium and iron carbonyl complexes relevant to the catalytic activation of carbon monoxide and of other small molecules will be reviewed.

Time-Resolved Infrared Spectral Studies of Photochemically Induced Oxidative Addition of Benzene to trans-RhCl(CO)(PMe3)2

“…The transient difference spectrum displays a bleaching at 1962 cm -1 representing the loss of 1 and a new, broad absorbance at 2050 cm -1 corresponding to the formation of an intermediate. When temporal absorbance changes in the IR were examined using a tunable single-frequency probe source, formation of the transient shows a prompt rise (within the 150 ns rise time of the system), consistent with direct reaction with the short-lived excited state as shown in Scheme (Figure inset). However, these data also indicate another process, a “delayed” rise of the absorbance attributed to 2 , which could be fit to a first-order rate law with k obs = (8.3 ± 1) × 10 4 s -1 .…”

Room-Temperature Reactions of the Intermediate(s) Generated by Flash Photolysis of (η5-C5H5)Fe(CO)2CH3

“…TRIR Spectra. The time-resolved infrared instrumentation with modifications in sample handling, has been described. 1b, After flash photolysis by XeCl excimer laser pulses at 308 nm (∼20 ns pulse length) to generate transient species, the temporal absorbances were recorded using a continuous IR probe source (lead salt diode laser system), operating at a single, but tunable, frequency, and a fast rise-time Hg/Cd/Te IR detector. Each absorbance vs time ( t ) trace was signal-averaged at least 30 times or until a good signal-to-noise ratio was obtained.…”