Robust and efficient amide-based nonheme manganese(III) hydrocarbon oxidation catalysts: substrate and solvent effects on involvement and partition of multiple active oxidants.

Two new mononuclear nonheme manganese(III) complexes of tetradentate ligands containing two deprotonated amide moieties, [Mn(bpc)Cl(H(2)O)] (1) and [Mn(Me(2)bpb)Cl(H(2)O)]⋅CH(3)OH (2), were prepared and characterized. Complex 2 has also been characterized by X-ray crystallography. Magnetic measurements revealed that the complexes are high spin (S = 5/2) Mn(III) species with typical magnetic moments of 4.76 and 4.95 µ(B), respectively. These nonheme Mn(III) complexes efficiently catalyzed olefin epoxidation and alcohol oxidation upon treatment with MCPBA under mild experimental conditions. Olefin epoxidation by these catalysts is proposed to involve the multiple active oxidants Mn(V)=O, Mn(IV)=O, and Mn(III)-OO(O)CR. Evidence for this approach was derived from reactivity and Hammett studies, KIE (k(H)/k(D)) values, H(2)(18)O-exchange experiments, and the use of peroxyphenylacetic acid as a mechanistic probe. In addition, it has been proposed that the participation of Mn(V)=O, Mn(IV)=O, and Mn(III)-OOR could be controlled by changing the substrate concentration, and that partitioning between heterolysis and homolysis of the O-O bond of a Mn-acylperoxo intermediate (Mn-OOC(O)R) might be significantly affected by the nature of solvent, and that the O-O bond of the Mn-OOC(O)R might proceed predominantly by heterolytic cleavage in protic solvent. Therefore, a discrete Mn(V)=O intermediate appeared to be the dominant reactive species in protic solvents. Furthermore, we have observed close similarities between these nonheme Mn(III) complex systems and Mn(saloph) catalysts previously reported, suggesting that this simultaneous operation of the three active oxidants might prevail in all the manganese-catalyzed olefin epoxidations, including Mn(salen), Mn(nonheme), and even Mn(porphyrin) complexes. This mechanism provides the greatest congruity with related oxidation reactions by using certain Mn complexes as catalysts.

Real-time detection of DNA cleavage induced by [M(2,2'-dipyridylamine)(2)(NO(3))(n)](x+) (M=Cd, Cu, Ni, Zn, n=1,2, x=0,1): effect of central metal ions.

[M(Hdpa)(2)(NO(3))(n)](x+) (M=Zn(II), Cd(II), Cu(II) and Ni(II), n=1,2, and x=0, 1) complexes were synthesized, and their activity as catalysts for DNA cleavage reactions were investigated using electrophoresis and linear dichroism technique (LD). All four metal complexes effectively cleaved pBR322 super-coiled DNA. The electrophoresis analysis showed that the [Zn(Hdpa)(2)(NO(3))](+) and [Cd(Hdpa)(2)(NO(3)) (2)] complexes most effectively cleaved the super-coiled DNA, whereas the [Ni(Hdpa)(2)(NO(3))](+) complex was least effective. The magnitude of LD in the DNA absorption region reflects the flexibility and length of DNA when the conditions for measurement are properly adjusted. The double stranded DNA cleavage increases the flexibility of DNA and reduces the length, reducing the magnitude of LD in DNA absorption region. Utilizing this LD property, the cleavage was detected in real-time by measuring the LD magnitude with respect to time. The decrease in the LD magnitude was described as the sum of two exponentials. The fast component was tentatively assigned to the cleavage of the single strand, reflecting the increase in the flexibility of DNA, and the slow component was assigned to the cut of the double strand which reduced the length of DNA. The average reaction time was the fastest for the Zn(II) complex and the slowest for the Ni(II) complex. The reaction time of the Cd(II) complex was as fast as that of the Zn(II) complex. Both the Zn(II) and Cd(II) belong to group 12, suggesting that [M(Hdpa)(2)(NO(3))(n)](x+) with central metal ions from group 12 most efficiently cleaved double stranded DNA.