291759-75-6Relevant academic research and scientific papers
Porphyrin-o-quinones as model systems for electron transfer and catecholase reactions
Speck, Marcus,Kurreck, Harry,Senge, Mathias O.
, p. 2303 - 2314 (2007/10/03)
Various porphyrin-o-quinones 1-8 were prepared as model compounds for electron transfer reactions. The synthesis of these compounds could only be accomplished by using o-quinone components stabilized by sterically demanding substituents in the o,o'-positions and by using protected catechol aldehydes for the initial porphyrin condensation step. The stability of the target compounds strongly depends on the steric influence of substituents on the o- quinone, which are necessary to stabilize the o-quinones. To test this steric influence we synthesized the porphyrin-o-quinones both without and with methyl and tert-butyl groups and investigated the influence of the bridging position on the reactivity. The 1H and 13C-NMR spectroscopic characteristics of all compounds are given: The electron transfer properties were determined using optical spectroscopy and cyclic voltammetry. The free base porphyrin-o-quinone 1 with two tert-butyl groups in the o,o'-positions of the quinone readily underwent degradation reactions to muconic acid derivatives similar to those observed in catecholase reactions. Nevertheless, this is the first report of such reactions that do not involve the addition of metal-containing-catalysts. The respective zinc(II) complex 6 and the two separated components tetraphenylporphyrin 26 and 3,6-di-tert-butyl-o-quinone (27) did not undergo this reaction, and we surmise a photochemical mechanism that depends on the steric demand of the o-quinone.
