-
Young Joo Song,
Sun Hwa Lee,
Hyun Min Park, Soo Hyun Kim,
Hyo Geun Goo,
Geun Hee Eom,
Ju Hoon Lee,
Myoung Soo Lah,
Youngmee Kim,
Sung-Jin Kim,
Ju Eun Lee,
Hong-In Lee,
Cheal Kim
[show abstract]
[hide abstract]
ABSTRACT: 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.
Chemistry 06/2011; 17(26):7336-44. · 5.93 Impact Factor
-
Chemistry 03/2010; 16(15):4678 - 4685. · 5.93 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Two new tetranuclear chalcocyanide cluster complexes, [{Mn(saloph)H(2)O}(4)Re(4)Q(4)(CN)(12)]4 CH(3)OH 8 H(2)O (saloph=N,N'-o-phenylenebis(salicylidenaminato), Q=Se (1-Se), Te (2-Te)), have been synthesized by the diffusion of a methanolic solution of [PPh(4)](4)[Re(4)Q(4)(CN)(12)] into a methanolic solution of [Mn(saloph)](+). The structure of 2-Te has been determined by X-ray crystallography. These rhenium cluster-supported [Mn(III)(saloph)] complexes have been found to efficiently catalyze a wide range of olefin epoxidations under mild experimental conditions in the presence of meta-chloroperbenzoic acid (mCPBA). Olefin epoxidation by these catalysts is proposed to involve the multiple active oxidants Mn(V)==O, Mn(IV)==O, and Mn(III)--OOC(O)R. Evidence in support of this interpretation has been derived from reactivity and Hammett studies, H(2) (18)O-exchange experiments, and the use of peroxyphenylacetic acid as a mechanistic probe. Moreover, it has been observed that the participation of Mn(V)==O, Mn(IV)==O, and Mn(III)--OOC(O)R can be controlled by changing the substrate concentration. This mechanism provides the greatest congruity with related oxidation reactions that employ certain Mn complexes as catalysts.
Chemistry 03/2010; 16(15):4678-4685. · 5.93 Impact Factor
-
Polyhedron 27(17):3484-3492. · 2.06 Impact Factor
