Efficient olefin epoxidation by robust Re4 cluster-supported Mn(III) complexes with peracids: evidence of simultaneous operation of multiple active oxidant species, Mn(V)=O, Mn(IV)=O, and Mn(III)-OOC(O)R.
Two new tetranuclear chalcocyanide cluster complexes, [{Mn(saloph)H2O}4Re4Q4(CN)12]⋅4 CH3OH⋅ 8 H2O (saloph = N,N'-o-phenylenebis(salicylidenaminato), Q = Se (1-Se), Te (2-Te)), have been synthesized by the diffusion of a methanolic solution of [PPh4]4[Re4Q4(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, H2(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.
Department of Fine Chemistry and Eco-Product and Materials Education Center, Seoul National University of Technology, Seoul 139-743 (Korea), Fax: (+82) 2-973-9149.
Sun Hwa
SH
Lee
Li
L
Xu
Byeong Kwon
BK
Park
Yuri V
YV
Mironov
Soo Hyun
SH
Kim
Young Ju
YJ
Song
Cheal
C
Kim
Youngmee
Y
Kim
Sung-Jin
SJ
Kim
D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D002723:Chlorobenzoates / Q000737:chemistry; D018360:Crystallography, X-Ray; D008345:Manganese / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D016877:Oxidants / Q000737:chemistry*; D010084:Oxidation-Reduction; D012211:Rhenium / Q000737:chemistry*
D000475:Alkenes; D002723:Chlorobenzoates; D009942:Organometallic Compounds; D016877:Oxidants; D008345:Manganese; D012211:Rhenium
cluster compounds; epoxidation; manganese; rhenium