Min Young Hyun

Remarkable Solvent, Porphyrin Ligand, and Substrate Effects on Participation of Multiple Active Oxidants in Manganese(III) Porphyrin Catalyzed Oxidation Reactions

The participation of multiple active oxidants generated from the reactions of two manganese(III) porphyrin complexes containing electron-withdrawing and -donating substituents with peroxyphenylacetic acid (PPAA) as a mechanistic probe was studied by carrying out catalytic oxidations of cyclohexene, 1-octene, and ethylbenzene in various solvent systems, namely, toluene, CH(2) Cl(2) , CH(3) CN, and H(2) O/CH(3) CN (1:4). With an increase in the concentration of the easy-to-oxidize substrate cyclohexene in the presence of [(TMP)MnCl] (1a) with electron-donating substituents, the ratio of heterolysis to homolysis increased gradually in all solvent systems, suggesting that [(TMP)Mn-OOC(O)R] species 2a is the major active species. When the substrate was changed from the easy-to-oxidize one (cyclohexene) to difficult-to-oxidize ones (1-octene and ethylbenzene), the ratio of heterolysis to homolysis increased a little or did not change. [(F(20) TPP)Mn-OOC(O)R] species 2b generated from the reaction of [(F(20) TPP)MnCl] (1b) with electron-withdrawing substituents and PPAA also gradually becomes involved in olefin epoxidation (although to a much lesser degree than with [(TMP)Mn-OOR] 2a) depending on the concentration of the easy-to-oxidize substrate cyclohexene in all aprotic solvent systems except for CH(3) CN, whereas Mn(V)=O species is the major active oxidant in the protic solvent system. With difficult-to-oxidize substrates, the ratio of heterolysis to homolysis did not vary except for 1-octene in toluene, indicating that a Mn(V)=O intermediate generated from the heterolytic cleavage of 2b becomes a major reactive species. We also studied the competitive epoxidations of cis-2-octene and trans-2-octene with two manganese(III) porphyrin complexes by meta-chloroperbenzoic acid (MCPBA) in various solvents under catalytic reaction conditions. The ratios of cis- to trans-2-octene oxide formed in the reactions of MCPBA varied depending on the substrate concentration, further supporting the contention that the reactions of manganese porphyrin complexes with peracids generate multiple reactive oxidizing intermediates.

Amide-Based Nonheme Cobalt(III) Olefin Epoxidation Catalyst: Partition of Multiple Active Oxidants CoVO, CoIVO, and CoIIIOO(O)CR

A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl(2)][Et(4)N] (1; H(2)bpc = 4,5-dichloro-1,2-bis(2-pyridine-2-carboxamido)benzene), was prepared and then characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy, and X-ray crystallography. This nonheme Co(III) complex catalyzes olefin epoxidation upon treatment with meta-chloroperbenzoic acid. It is proposed that complex 1 shows partitioning between the heterolytic and homolytic cleavage of an O-O bond to afford Co(V)=O (3) and Co(IV)=O (4) intermediates, proposed to be responsible for the stereospecific olefin epoxidation and radical-type oxidations, respectively. Moreover, under extreme conditions, in which the concentration of an active substrate is very high, the Co-OOC(O)R (2) species is a possible reactive species for epoxidation. Furthermore, partitioning between heterolysis and homolysis of the O-O bond of the intermediate 2 might be very sensitive to the nature of the solvent, and the O-O bond of the Co-OOC(O)R species might proceed predominantly by heterolytic cleavage, even in the presence of small amounts of protic solvent, to produce a discrete Co(V) O intermediate as the dominant reactive species. Evidence for these multiple active oxidants was derived from product analysis, the use of peroxyphenylacetic acid as the peracid, and EPR measurements. The results suggest that a less accessible Co(V)=O moiety can form in a system in which the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors.

catena-Poly[[tetra-aqua-[trans-1,2-bis-(4-pyrid-yl)ethene-κN:N']nickel(II)] dinitrate].

In the title compound, {[Ni(C12H10N2)(H2O)4](NO3)2}n, the NiII ion, lying on a crystallographic inversion center, has a distorted octahedral coordination sphere comprising four water ligands and two N-atom donors from the trans-related 1,2-bis(4-pyridyl)ethene ligands, which also have crystallographic inversion symmetry. These ligands bridge the NiII complex units, forming chains extending along the [110] and [10] directions. The nitrate counter-anions stabilize the crystal structure through water–nitrate O—H⋯O hydrogen bonds.

catena-Poly[[bis-(2,4-dichloro-benzoato)bis-(methanol-κO)cobalt(II)]-μ-4,4'-bipyridine-κN:N'].

In the title compound, [Co(C7H3Cl2O2)2(C10H8N2)(CH3OH)2]n, the CoII ion lies on a twofold rotation axis and is in a slightly distorted octahedral CdO4N2 environment, formed by two O atoms from monodentate dichlorobenzoate ligands, two O atoms from methanol ligands, and two N atoms from trans-related 4,4′-bipyridine ligands. The bipyridine ligands also lies on a twofold rotation axis and bridge the CoII ions, forming chains extending along [010]. An intrachain O—H⋯O hydrogen bond is observed.