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X 104 M'1 cm'1. Again the excited electron preferentially resides in the bpm moiety, and the localized picture, over the time scale of the experiment, is further enhanced.Acknowledgment. The bulk of the experiments reported were perforemd at the Center for Fast Kinetics Research (CFKR). The CFKR is supported jointly by the Biomedical Research Technology Program of the Division of Research Resources of NIH (RR 00886) and by the University of Texas at Austin. A British Council Fellowship and the continuing support of the Yarmouk University Research Fund is gratefully acknolwedged (T. A.).

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A series of new cobalt(III)-, iron(III)-, and chromium(III)-based complexes of the general formula [M(N∩O)2Cl] (N∩O: N-salicylidene(X)amine and sodium N-(4-sulfonatosalicylidene(X)amine)) (X = cyclohexyl and 1-naphthyl) was prepared and characterized. Some of the isolated complexes have been evaluated as catalysts for the oxidation of L-cysteine. Preliminary results show that the rate of oxidation of L-cysteine is influenced by the nature of the metal center, the geometry of the complex, the auxiliary substituents, and the backbone of the ligand.

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Kinetics of oxidation of L-cysteine by pairs of trans and racemic cis isomers of cobalt(III) and iron(III) based transition metal complexes have been studied in aqueous solution. Kinetics measurements were run under pseudo first order conditions in which the concentration of cysteine is between one and two orders of magnitude greater than that of the isomers of the transition metal complex. The orders of the reaction with respect to both cysteine and the isomer were determined.The observed rate constants and the overall rate constants of the oxidation process were measured. For all geometrical isomers, it was found that the rate constant of oxidation of L-cysteine by the trans isomer is between one to three orders of magnitude greater than that by the cis isomer. The difference in rates can be explained by a geometric factor around the metal ion center in the complex. The less crowded isomer (trans) makes electron transfer easier and hence facilitates the oxidation process which leads to a higher oxidation rate.

The synthesis of a new series of trans and racemic cis isomers of cobalt(III)-, iron(III)-, and chromium(III)-based complexes with the α-and γ-diimine Schiff base ligands, N,NЈ-bis(X)-2,3-butandiimine and N,NЈ-bis(X)-1,2-phenyldiimine (X ϭ cyclohexyl, 2-isopropylphenyl, 1-naphthyl) is described. To confirm the identity of the complexes prepared in the present study, a variety of techniques including elemental analysis, magnetic susceptibility, infrared-, mass-(EI), and UV/Vis-spectroscopy have been utilized.Some of the isolated complexes have been evaluated as catalysts for the oxidation of L-cysteine. Preliminary results showed that the metal atoms, geometry of the complexes, auxiliary substituents, and the backbone of the ligand influenced the rate of oxidation reaction. Recently, we have reported that the rates of oxidation of L-cysteine by pairs of trans-and racemic cis-isomers of Co III -and Fe III -complexes bearing the ligands, ethylenedi-Scheme 2 Synthesis and suggested structures of Co(III)-, Fe(III)-, and Cr(III)-based α-diimine complexes (6Ϫ11) Z. Anorg. Allg. Chem. 2008, 956Ϫ961

A new series of penta-coordinated Co(III)-, Fe(III)-, and Cr(III)-complexes (6-10) bearing N-salicylidineisopropylaniline and sodium N-(4-sulfonitsalicylidineisopropyl-aniline) ligands has been synthesized and utilized, after activation with methyl aluminoxane, as catalysts for the polymerization of tert-butylacrylate (t-BA). High molar mass P(t-BA) polymers with very low molecular weight distributions were produced (M w /M n = 1.06-1.09). Cobalt-and chromium-based precatalysts showed higher activity towards the polymerization reaction than those of the iron complexes. The presence of sulfonated groups on the para position of the aryl group in the backbone of the ligand decreases the catalytic activity of the complexes. The ortho alkyl substituents on the aryl groups of the ligand have a favorable influence on the polymerization activity compared to the alkyl-free analogue (11).