Synthesis, X-ray Structure, Electrochemical, and EPR Studies of a Pentacoordinated Mn(II) Tetramethylcyclam Complex

摘要

It is well-known that manganese has a fundamental importance inbioinorganic chemistry. Particularly, over the past decade ther has been a considerable interest in synthesizing biomimetic complexes that can act as manganoenzymes such as superoxide dismutase (SOD).~(1,2) In this field of great interest, linear polyamines and polyazamacrocycles have been extensively studied because of their possible relevance to these biological systems. For example, many complexes based on tri-, tetra-, or pentaazamacrocycles~(3-7) as well as porphyrins~(8-10) have been shown to exhibit interesting catalytic activities. Among them, several manganese cyclam complexes have been well characterized like a mixed valence Mn(III)-Mn(IV) derivative,~(11-13) C-substituted Mn(III) derivatives,~(14,15) and unsubstituted manganese(III) cyclam derivatives.~(16-18) As part of our work on the coordiantion chemistry of substituted cyclam macro-cycles,~(19,20) we investigated the complexation of manganese with the 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (tmc). In accordance with the well-established steric and electronic influences of N-substitution,~(21-25) and contrary to the case of the unsubstituted homologues, no Mn(III) or dimer mixed valence species could be obtained.