FLOWING AFTERGLOW STUDIES OF GAS-PHASE ANIONIC TRANSITION-METAL CHEMISTRY (NUCLEOPHILIC ADDITION, BOND ENERGIES, OXIDATION, CARBONYLS)

KELLEY RAY LANE, Purdue University

Abstract

The flowing afterglow technique was used to investigate the gas phase reactions of anionic nucleophiles and negative ion clusters with several transition metal carbonyls and organometallic complexes. The reactions of many anionic transition metal complexes with small molecules were also examined. The experimental system is described and the data analysis is presented. An extensive series of anion reactants possessing a wide range of basicities, heteroatoms and molecular sizes have been reacted with Fe(CO)(,5) and the results have revealed a general mechanism wherein nucleophilic addition of the ion at a carbonyl is followed by expulsion of 0, 1, or 2 CO ligands from the metal. An analysis of the observed trends indicated that the extent of CO loss is directly related to the basicity and size of the attacking anion as well as the type of heteroatom which is present at the nucleophilic site of the anion. To help rationalize the basicity/reactivity relationship, the binding energies of Fe(CO)(,5) to a number of anions D (CO)(,4)FeC(O)-X('-) were determined from ion transfer reactions and equilibrium measurements. Direct comparison of the binding energies with other available affinity data for the anions resulted in two correlations which were used in the prediction of other Fe(CO)(,5)/anion binding energies. From the D (CO)(,4)FeC(O)-X('-) values, additional thermochemical information was derived for a series iron tetracarbonyl-acyl anions. These data are discussed in light of their relevance to homogeneous catalysis. An investigation of gas phase hydride transfer reactions provided hydride binding energies for a number of transition metal carbonyl complexes. These hydride binding energies were used to determine the heats of formation for several metal formyl anions which are of importance in catalytic reduction of CO. The direct reaction of hydride ion with a series of transition metal complexes was found to produce coordinatively unsaturated metal hydrides. The mechanisms of these reactions are discussed and the reactions of the metal hydrides with small molecules are described. The oxidation of anionic transition metal complexes with O(,2) is also described. These oxidation reactions yielded an array of metal carbonyl oxide and polyoxide ion products. The different product distributions for the different metal complexes are rationalized and a theoretical analysis of the structures for CrO(,n)('-), n = 1-5 is presented. The structures and reactivity of several C(,2)HCl(,2)('-) isomers and the C(,2)Cl(,3)('-) ion were also examined and it was concluded that the C(,2)HCl(,2)('-) ion derived by proton abstraction from trans-1,2-dichloroethylene possesses a vinylic anion structure.

Degree

Ph.D.

Subject Area

Chemistry

COinS