B.S. University of Wisconsin, 1958
PhD. University of California, Berkeley, 1961
Dr. Krueger's research involves the synthesis of transition-metal complexes and detailed studies of the kinetics and mechanism of reactions which they undergo. Of particular interest is the stabilization and characterization of reactive functional groups through binding to a metal ion.
Alkyl sulfenates, -CH2SO-, are too reactive to exist in the free-ligand state, but have been stabilized in cobalt (III) complexes. For example, they have been studying the synthesis of several sulfenato stereoisomers formed from H202 oxidation of CoIII(PenS)2-. PenS represents the sulfur amino acid, penicillamine, in the anion form, SC(CH3)2CH(COO-) NH2. A stable monosulfenato complex is shown in the figure below.
The results of a kinetics study indicate that the hydrogen peroxide oxidation reaction proceeds via a nucleophilic substitution pathway. The coordinated sulfenate sulfur is a chiral center. Optical isomerization occurs and this can be followed using the technique of circular dichroism spectroscopy.
Sulfenates are believed to be intermediates in some biological reactions involving oxidation of thiolates such as cysteine and penicillamine. They are interested in finding new ways of stabilizing sulfenates to study their role as intermediates. It appears that coordination to an iron center is an important feature of these oxidative processes. Thus, the chemistry of thiolato iron complexes is under investigation.
The sulfenamide group, -CH2SNH2, is another reactive group reactivity that is modified by coordination to a metal center. Formation and characterization of (en)2 Co-[S(NH2)CH2CH(COO)-NH2]2+, and its base-catalyzed isomerization and hydrolysis are being investigated.
A variety of analytical nad physical techniques are utilized in characterizing the complexes: chromatographic separation of the species, identification by UV-visible, 1H and 13C NMR, circular dichroism, and IR spectroscopy, stopped-flow kinetics measurements for following rapid reactions, and x-ray diffraction to determine structure.