Detection of Transient Organometallic Species by Fast Time-Resolved IR Spectroscopy

This chapter discusses the role of matrix isolation in characterizing transition-metal fragments and then considers what conventional flash photolysis with uv-vis detection has revealed about the reactivity of these fragments. It is the timescale of these reactions that dictates the speed of the infrared (IR) spectroscopy required to detect the intermediates. The principles of these new IR techniques are explained and the apparatus involved is described. The chapter presents a self-contained summary of the organometallic chemistry that has already been unraveled by time-resolved IR spectroscopy. The basic principles of matrix isolation are relatively well known, and its application to organometallic chemistry has been recently reviewed. Many of the species generated in low-temperature matrices are coordinatively saturated species. Unlike the unsaturated transition-metal fragments, these species may have significant activation barriers for reaction or decomposition and can be stabilized by merely lowering the temperature. IR kinetic spectroscopy involves uv flash generation of transients and monitoring of transients at a finite number of IR wavelengths. There have been three primary motives behind the study of metal–carbonyl photochemistry in the gas phase: to discover the shapes of metal–carbonyl fragments in the absence of perturbing solvents or matrices, to probe the effect of uv photolysis wavelength on product distribution, and to measure the reaction kinetics of carbonyl fragments.