INVESTIGATIONS OF OXYGEN REACTIVITY WITH SYNTHETIC COPPER(I), IRON(II), COBALT(II), AND COBALT(I) COMPLEXES DERIVED FROM NITROGENOUS PENTADENTATE LIGANDS

[摘要] The {bis-2,6-{1-(2-imidazol-4-ylethylimino)ethyl}pyridine}copper(I) cation, {Cu(I)(imidH)(,2)DAP}('+), has previously been reported to react reversibly with O(,2) in a 2:1 stoichiometry under ambient conditions in solution, thus providing a copper(I) complex to model the active site function of hemocyanin {J. Chem. Soc. (Dalton), 1827 (1980)}. The reactivity of O(,2) with other closely related derivatives of this complex has been previously studied, with those derivatives found to be either less reversible in their reactivity with O(,2) or to be unreactive toward O(,2). In the present work, a new, closely related series of copper(I) derivatives, {Cu(I)(imidH)(,2)PDA}('+), {Cu(I)(imidR)(,2)PDA}('+), and {Cu(I)(py)(,2)PDA}('+), have been synthesized, characterized, and their reaction with O(,2) studied in order to better understand what determines the degree of reversible O(,2) reactivity. These new complexes were found to be either unreactive with O(,2) or their reactivity to be less reversible than that of the previously studied parent complexes. It was found possible to relate the O(,2) reactivity and degree of reversibility to the E(, 1/2) of the copper center for a series of closely related complexes. The zinc(II) and copper(II) complexes were also synthesized and characterized for comparison.In a continuing study of O(,2) reactivity with transition metal complexes, the ligand systems {(imidH)(,2)DAP} and {(py)(,2)DAP} were studied with iron(II) to investigate the possibility that these complexes might also serve as model compounds for the active site function of hemerythrin. Whereas {Fe(II)(py)(,2)DAP}(BF(,4))(,2) was found to be unreactive with O(,2), {Fe(II)(imidH)(,2)DAP}(BF(,4))(,2) was found to react slowly and irreversibly under ambient conditions in a ratio of one O(,2) molecule per iron center.As there are now many known cobalt(II) O(,2)-carriers, these same ligands were also studied with cobalt as the metal center. The {Co(II)(py)(,2)DAP}(BF(,4))(,2) complex was found to be unreactive toward O(,2), whereas both {Co(I)(py)(,2)DAP}(BF(,4)) and {Co(II)(imidH)(,2)DAP}(BF(,4))(,2) reacted slowly and irreversibly with O(,2) in a ratio of one O(,2) molecule per cobalt center. In addition, {Co(II)(imidH)(,2)DAP}(BF(,4))(,2) yielded an isolatable and characterizable monomeric cobalt-O(,2) complex.In summary, a total of fifteen new complexes of zinc(II), copper(II), copper(I), iron(II), cobalt(II) and cobalt(I) were synthesized, characterized, and studied for reversible reactivity with O(,2), with some insight gained into the mechanism responsible for irreversible oxidation of the O(,2) reactive complexes.

[发布机构] Rice University

[效力级别] chemistry