SOLVENT AND STRUCTURAL EFFECTS ON CATALASE-LIKE FUNCTION OF BINUCLEARMANGANESE(II) COMPOUNDS WITH MU-PHENOXIDE BRIDGE

The structures and ESR spectral properties of binuclear manganese(II) compounds which functionally mimic the bacterial dimanganese catalase enzyme have been developed. These compounds are formulated as [(L-1)Mn 2X2]Y(X=Cl, Br, CH3COO, C6H5COO, (C6H5)(2)HCCOO; Y=ClO4, PF6), [(L-2)( MnX3)-X-2] (X=Cl, Br), and [(L-2)Mn-2(benzoate)(2) (NCS)], where H(L-1 )=2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4- methyl-phenol and 2,6-bi s[N-(2-dimethylamino)ethyl]-4-methyl-phenol. An X-ray diffraction stru cture determination of [(L-1)Mn2Cl2(CH3OH)(2)]PF6 confirmed the antici pated N6O septadentate coordination of the (L-1)-ligand, binuclear man ganese(II) complex with mu-phenoxide, and two halogenide ions and two methanol molecules. In the crystal of [(L-2)Mn2Cl3]CH3CN, there exists tetranuclear manganese(II) complex having center of symmetry. The ter minal and central manganese(II) ions are bridged by phenoxide oxygen a nd a chloride ion (Mn Mn = 3.440(1) Angstrom), and two central atoms a re bridged by two chloride ions with Mn Mn distance of 3.804(1) Angstr om. In acetonitrile solution, catalase-like function of the manganese( II) compounds with H(L-1)-ligand are found to be highly dependent the anions coordinating the Mn(II) ion, the activity of the X=Cl complex i s much higher than those of the acetate and benzoate. On the other han d, the activity of [(L-2)Mn2Cl3] is slightly lower than that of the [( L-2)Mn-2(benzoate)(2)(NCS)], where two manganese ions are bridged by b enzoate anion. The Mn(II/III) complex of H(L-1), [(L-1)Mn-2(CH3COO)(2) ](2+) exhibits much higher activity than that of the corresponding Mn( II/III) complex, [(L-1)Mn-2(CH3COO)(2)](+). In dimethylformamide(dmf) solutions, an induction period (at least 30 minutes) is necessary befo re vigorous evolution of oxygen gas occurs for both the Mn(II) complex es with (L-1) and (L-2), however, some binuclear Mn-2(II/III) and Mn-2 (III/III) complexes exhibited high catalase-like function in dmf. The latter fact may give a reasonable explanation for the fact that the ma nganese cluster in S-2-state of the Photosystem II shows a high catala se-like function instead of the negligible action in the S-1-state. Ba sed on these facts, it is concluded that the most important factor to control the catalase-like function of binuclear Mn(IE) complex should be the oxidizable nature of the Mn(II) ion to a higher oxidation state , and the unusual behavior in dmf solution was accounted for on the as sumption that dmf molecule may contribute to the activation of peroxid e ion through interaction with an Mn(II)-peroxide adduct, leading to o xidation of the Mn(II) ion. (C) 1997 Elsevier Science Ltd.