Electron Transfer Chemistry of Organometallic Porphyrins

烷基和芳基金属σ-键合的卟啉的单电子氧化之后通常是σ-键合的有机配体的金属到氮的迁移。本<III><IV>研究结合电化学、紫外-可见光谱、ESR和停流动力学研究了（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 =取代卟啉的二价阴离子：TPP或OEP，M = Co或Fe，R = n-Bu、Et、Me或Ph，L =乙腈或取代的吡啶。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，钴-碳键的断裂通过从R到Co的速率决定性的分子内电子转移发生，这导致R基团的金属到氮的迁移。以类似的方式，芳基σ键合的铁卟啉（OEP）Fe^（R）的单电子氧化<III>导致Fe^中心的形成<IV>，其总是在迁移之前产生。

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.