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Relevant academic research and scientific papers

Hydrocarbon oxidation by bis-μ-oxo manganese dimers: Electron transfer, hydride transfer, and hydrogen atom transfer mechanisms

Described here are oxidations of alkylaromatic compounds by dimanganese μ-xo and μ-hydroxo dimers [(phen)2MnIV (μ-O)2MnIV(phen)2]4+ ([Mn2(O)2]4+), [(phen)2MnIV (μ-O)2MnIII(phen)2]3+ ([Mn2(O)2]3+), and [(phen)2MnIII (μ-O)(μ-OH)MnIII(phen)2]3+ ([Mn2(O)(OH)]3+). Dihydroanthracene, xanthene, and fluorene are oxidized by [Mn2(O)2]3+ to give anthracene, bixanthenyl, and bifluorenyl, respectively. The manganese product is the bis(hydroxide) dimer, [(phen)2MnIII (μ-OH)2Mn(phen)2]3+ ([Mn2(OH)2]3+). Global analysis of the UV/vis spectral kinetic data shows a consecutive reaction with buildup and decay of [Mn2(O)(OH)]3+ as an intermediate. The kinetics and products indicate a mechanism of hydrogen atom transfers from the substrates to oxo groups of [Mn2(O)2]3+ and [Mn2(O)(OH)]3+. [Mn2(O)2]4+ is a much stronger oxidant, converting toluene to tolyl-phenylmethanes and naphthalene to binaphthyl. Kinetic and mechanistic data indicate a mechanism of initial preequilibrium electron transfer for p-methoxytoluene and naphthalenes because, for instance, the reactions are inhibited by addition of [Mn2(O)2]3+. The oxidation of toluene by [Mn2(O)2]4+, however, is not inhibited by [Mn2(O)2]3+. Oxidation of a mixture of C6H5CH3 and C6H5CD3 shows a kinetic isotope effect of 4.3 ± 0.8, consistent with C-H bond cleavage in the rate-determining step. The data indicate a mechanism of initial hydride transfer from toluene to [Mn2(O)2]4+. Thus, oxidations by manganese oxo dimers occur by three different mechanisms: hydrogen atom transfer, electron transfer, and hydride transfer. The thermodynamics of e-, H?, and H- transfers have been determined from redox potential and pKa measurements. For a particular oxidant and a particular substrate, the choice of mechanism is influenced both by the thermochemistry and by the intrinsic barriers. Rate constants for hydrogen atom abstraction by [Mn2(O)2]3+ and [Mn2(O)(OH)]3+ are consistent with their 79 and 75 kcal mol-1 affinities for H?. In the oxidation of p-methoxytoluene by [Mn2(O)2]4+, hydride transfer is thermochemically 24 kcal mol-1 more facile than electron transfer; yet the latter mechanism is preferred. Thus, electron transfer has a substantially smaller intrinsic barrier than does hydride transfer in this system.

Diamino compounds and methods for preparing them

An object of the invention is to propose diamino compounds expressed by the following general formula (1) which are suitable to obtain a raw material, a polyimide resin, for a liquid crystal aligning film without any image sticking and with a high voltage holding ratio at from a low temperature to a high temperature as well as the preparation thereof: STR1