Département de chimie moléculaire

Reactions of MnII(PF6)2 and MnII(O2CCH3)2·4H2O with the tridentate facially capping ligand N,N-bis(2-pyridylmethyl)ethylamine (bpea) in EtOH solns. afforded the mononuclear [MnII(bpea)](PF6)2 (1) and the new binuclear [MnII,II2($μ$-O2CCH3)3(bpea)2](PF6) (2) Mn(II) compds., resp. Both 1 and 2 were characterized by x-ray crystallog. studies. Complex 1 crystallizes in the monoclinic system, space group P21/n, with a 11.9288(7), b 22.5424(13), c 13.0773(7) {\AA}, $\alpha$ 90., $\beta$ = 100.5780(10°), $\gamma$ 90.°, and Z = 4. Crystals of complex 2 are orthorhombic, space group C2221, with a 12.5686(16), b 14.4059(16), c 22.515(3) {\AA}, $\alpha$ 90., $\beta$ 90., $\gamma$ 90.°, and Z = 4. The three acetates bridge the two Mn(II) centers in a $μ$1,3 syn-syn mode, with a Mn-Mn sepn. of 3.915 {\AA}. A detailed study of the electrochem. behavior of 1 and 2 in MeCN medium was made. Successive controlled potential oxidns. at 0.6 and 0.9 V vs. Ag/Ag+ for a 10 mM soln. of 2 allowed the selective and nearly quant. formation of [MnIII2($μ$-O)($μ$-O2CCH3)2(bpea)2]2+ (3) and [MnIV2($μ$-O)2($μ$-O2CCH3)(bpea)2]3+ (4), resp. These results showed that each substitution of an acetate group by an oxo group is induced by a two-electron oxidn. of the corresponding dimanganese complexes. Similar transformations were obtained if 2 is formed in situ either by direct mixing of Mn2+ cations, bpea ligand, and CH3COO- anions with a 1:1:3 stoichiometry or by mixing of 1 and CH3COO- with a 1:1.5 stoichiometry. Assocd. electrochem. back-transformations were studied. 2, 3, And the dimanganese [MnIIIMnIV($μ$-O)2($μ$-O2CCH3)(bpea)2]2+ analog (5) were also studied for their ability to disproportionate H2O2. 2 Is far more active compared to 3 and 5. The EPR monitoring of the catalase-like activity showed that the same species are present in the reaction mixt. abeit in slightly different proportions. 2 Operates probably along a mechanism different from that of 3 and 5, and the formation of 3 competes with the disproportionation reaction catalyzed by 2. Indeed a soln. of 2 exhibits the same activity as 3 for the disproportionation reaction of a 2nd batch of H2O2 indicating that 3 is formed in the reaction. [on SciFinder(R)]