Oxidations of hydrocarbons by manganese(III) tris(hexafluoroacetylacetonate).
Mn(hfacac)(3) is an easily prepared and reactive oxidant (hfacac = hexafluoroacetylacetonate). It forms stable solutions in benzene and methylene chloride but is rapidly reduced in acetonitrile, DMSO, acetone, and ethers. It is reduced by ferrocene to give the Mn(II) complex [Cp(2)Fe][Mn(hfacac)(3)], which has been structurally characterized. Mn(hfacac)(3) also rapidly oxidizes 1-acetylferrocene, 1,1'-diacetylferrocene, and tris(4-bromophenyl)amine. Based on an equilibrium established with tris(2,4-dibromophenyl)amine, a redox potential of 0.9 +/- 0.1 V vs Cp(2)Fe(+/0) is calculated. Mn(hfacac)(3) oxidizes 9,10-dihydroanthracene (DHA) cleanly to anthracene, with a bimolecular rate constant of 6.8 x 10(-4) M(-1) s(-1) at 25 degrees C in benzene solution. In the presence of small amounts of water, the manganese(II) product is isolated as cis-Mn(hfacac)(2)(H(2)O)(2), which has also been structurally characterized. Mn(hfacac)(3) also oxidizes xanthene to 9,9'-bixanthene, 1,4-cyclohexadiene to benzene, and 2,4-di-tert-butylphenol to the phenol dimer. Toluene and substituted toluenes are oxidized to tolylphenylmethanes. Product analyses and relative rates--for instance that p-methoxytoluene reacts much faster than toluene--indicate that the more electron rich substrates react by initial electron transfer to manganese. For the less electron rich substrates, such as 1,4-cyclohexadiene, a mechanism of initial hydrogen atom transfer to Mn(hfacac)(3) is suggested. The ability of Mn(hfacac)(3) to abstract H* is reasonable given its high redox potential and the basicity of [Mn(hfacac)(3)](-). In CH(2)Cl(2) solution, oxidation of DHA is catalyzed by chloride ion.
Bryant
Jasmine R
JR
Department of Chemistry, Box 351700, University of Washington, Seattle, Washington 98195-1700, USA.
Taves
Janelle E
JE
Mayer
James M
JM
D000096:Acetone; D000097:Acetonitriles; D000588:Amines / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray; D004121:Dimethyl Sulfoxide; D004578:Electron Spin Resonance Spectroscopy; D004987:Ethers; D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008345:Manganese / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen
D000097:Acetonitriles; D000588:Amines; D004987:Ethers; D006841:Hydrocarbons, Aromatic; D009942:Organometallic Compounds; C465091:manganese(III) tris(hexafluoroacetylacetonate); D000096:Acetone; D008345:Manganese; D010100:Oxygen; D004121:Dimethyl Sulfoxide; C032159:acetonitrile