Electron Transfer Chemistry of Organometallic Porphyrins

烷基和芳基金属sigma键卟啉的单电子氧化通常伴随着sigma键有机配体的金属向氮迁移。对氧化钴sigma键卟啉的一些研究表明，在迁移之前会产生Co^<III>阳离子自由基，而不是Co^<IV>阳离子。本研究结合了电化学、紫外可见光谱和ESR光谱以及停止流动动力学的使用，研究了(P) M (R)和(P) M (R)(L)型单氧化有机卟啉的反应和性质，其中P =取代卟啉的离子：TPP或OEP，M = Co或Fe， R = n-Bu, Et， Me或Ph， L =乙腈或取代吡啶。我们的研究结果清楚地表明，（TPP） Co^<IV> (R)配合物可以在特定的溶液条件下生成，并且通过从R到Co的速率决定的分子内电子转移发生钴碳键的裂解，这导致R基团的金属向氮迁移。以类似的方式，芳基sigma键铁卟啉（OEP） Fe^<III> (R)的单电子氧化导致Fe^<IV>中心的形成，该中心总是在迁移之前生成。

The one-electron oxidation of alkyl and aryl metal sigma-bonded porphyrins is often followed by a metal to nitrogen migration of the sigma-bonded organic ligand. Several studies of oxidized cobalt sigma-bonded porphyrins have suggested that a Co^<III> pi cation radical rather than a Co^<IV> cation is generated prior to the migration.The present study combines the use of electrochemistry, UV-vis and ESR spectroscopy and stopped flow kinetics to investigate the reactions and properties of singly oxidized organoporphyrins of the type (P) M (R) and (P) M (R)(L) where P = the dianion of substituted porphyrins : TPP or OEP,M = Co or Fe, R = n-Bu, Et, Me or Ph, L = acetonitrile or a substituted pyridine. The results of our studies show clearly that a (TPP) Co^<IV> (R) complex can be generated under specific solution conditions and the cleavage of the cobalt-carbon bond occurs via a rate-determining intramolecular electron transfer from R to Co and this results in a metal to nitrogen migration of the R group. In a similar mannar, one-electron oxidation of an aryl sigma-bonded iron porphyrin, (OEP) Fe^<III> (R) results in the formation of an Fe^<IV> center which is invariably generated prior to migration.