Doctoral Dissertations

Date of Award

5-1993

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Clifton Woods, III

Committee Members

Gilbert M. Brown, D. Paul Rillema, Kelsey D. Cook

Abstract

Spectroscopic behaviors of dpam-containing (dpam=bis(diphenylarsino)- methane) dirhodium-μ-pyrazolato A-frame complexes have been compared to those of the (diphenylarsino)(diphenylphosphino)methane (dapm) and bls(diphenylphosphino)methane (dppm) analogs through ligand substitution and electrochemical oxidation. Thermochromism of isocyanide-containing dirhodium(l,ll) compounds has been examined. To clarify the role of electronegativity of pyrazolate substituents in inducing thermochromism, dapm and dppm dirhodium A-frame species containing trifluoromethylpyrazole ligands have been examined. increases in electronegativity of pyrazole substituents have been shown to cause decreases in the thermochromic isomerization temperature. Examination of dirhodium-μ-hydroxypyridinato A-frame complexes has been undertaken to evaluate spectroscopic and structural effects of bifunctional asymmetric bridgehead ligands with π systems that might induce thermochromism similar to that of the pyrazolate complexes. Neither one-electron oxidized dirhodium-μ-hydroxypyridinato species nor those containing dpam or isocyanide could be isolated. Spectroscopic properties of the complexes synthesized were similar to those of dirhodlum-μ-pyrazole analogs. Fluxional behavior of μ-hydroxypyridinate ligands was characterized using 31P NMR. This fluxional behavior depends on the bis-transoid bridges and on the 6-substitution of the hydroxypyridinate ligand. Crystal structures of two dirhodium-μ.-hydroxypyridinato compounds have shown that hydroxypyridinate coordination is bidentate in the solid state. The crystal structure of an unexpected trirhodium species, [Rh3(μ-dppm)2(μ-CO)3(CO)3][PF6], has been determined. Fast atom bombardment (FAB) and collision-induced dissociation (CID) mass spectrometries were used to study certain dirhodium-μ-pyrazolato A-frame complexes. Both the atom beam and m-nitrobenzyl alcohol have been shown to promote redox reactions of certain of the complexes examined by FAB. Analysis of FAB spectra were complicated by species formed by beam- and matrix-induced damage. CID tandem mass spectrometry allowed more accurate structural interpretation. Dirhodium fragmentation can be understood by correlation with reactivities of similar complexes. Kinetics of the disproportionation of the dirhodium (1,11) bis(isocyanide) complexes with halide in methylene chloride were examined. Complex reaction kinetics were not successfully modelled. A study of initial rates Indicated the reaction to be first order in dirhodium(l,ll) species and to depend on chloride in a variable but explicable fashion.

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