Elementary rate constants and thermal activation parameters for the gas phase unimolecular decomposition of group VI metal olefin complexes
Abstract
The thermal decomposition of a number of metal olefin complexes is followed in the gas phase, using infrared radiation as a probe. The thesis is divided into two parts preceded by an introduction. Part One reports elementary rates and activation data for the CO-for-ethylene exchange reaction on photoprepared Cr(CO)$\sb5.$ Experimental procedure and instrumental performance are evaluated. Part Two discusses the construction of a transient infrared absorption spectrophotometer and also evaluates the signal to noise characteristics of this instrument. Additionally, Part Two presents further results on the relative labilities of a series of Cr(CO)$\sb5$(olefin) complexes. The activation data presented here are the first to stress the importance of statistical effects in unimolecular decomposition of metal-ligand complexes. Elementary rates of complex formation indicate that olefin association with the unsaturated metal center is faster than CO recombination, suggesting that electronic effects influence the capture event. Empirical results for unimolecular decomposition for the Cr(CO)$\sb5$(olefin) systems are supported by RRKM calculations. An increase in decomposition rate for successively more complex olefins may be explained almost wholly by gains in the rotational and vibrational partition functions of the complex relative to the transition state complex. Solution phase accounts of the effect of increasing fluorine substitution in metal olefin complexes suggest a bifurcation in the bonding mode of these ligands. Rates of decomposition and activation data are reported for some fluorinated and perfluorinated olefin complexes of Cr(CO)$\sb6$ and Fe(CO)$\sb5.$
Degree
Ph.D.
Advisors
Grant, Purdue University.
Subject Area
Chemistry|Chemistry
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