Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA.
Inorg Chem. 2010 Feb 1;49(3):1027-38. doi: 10.1021/ic901851u.
A series of cobalt(II) and cobalt(III) porphyrins with fused quinoxaline rings at one or more beta,beta'-pyrrolic units of the macrocycle were synthesized and characterized as to their electrochemical properties in nonaqueous media. Their UV-visible spectra were also measured before and during oxidation or reduction in a thin-layer cell. The investigated quinoxalinoporphyrins are represented as (PQ)Co, (QPQ)CoCl, (PQ(2))CoCl, Co(P)-TA-(P)Co, and Co(PQ)-(QP)Co, where PQ = the dianion of 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-quinoxalino[2,3-b']porphyrin, QPQ = the dianion of the corresponding linear bisquinoxalino[2,3-b':12,13-b'']porphyrin, PQ(2) = the dianion of the corresponding corner bisquinoxalino[2,3-b':7,8-b'']porphyrin, and (P)-TA-(P) = the tetraanion of the bis-porphyrin with 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrins fused at opposite ends of tetraazaanthracene. (P)Co and (P)CoCl were also characterized where P = the dianion of 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin. Each compound could be cycled between their Co(III), Co(II), and Co(I) forms under the application of a given oxidizing or reducing potential, although a one-electron reduction of the Co(II) quinoxalinoporphyrins led to a product with mixed Co(I) and porphyrin pi-anion radical character followed by generation of a pure Co(I) pi-anion radical species at more negative potentials. The effect of the position and number of quinoxaline groups on the redox potentials and mechanisms of each electron transfer were elucidated, and comparisons made to structurally similar compounds containing both redox active and redox inactive central metal ions. Surprisingly, the position and number of quinoxaline groups on the macrocycle has little or no effect on the redox potentials for the Co(II) --> Co(III) or Co(III) --> Co(II) processes, but this is not the case for other electron transfer reactions where significant differences are seen between the examined compounds. Significant interactions are also observed between the two porphyrin macrocycles of the laterally bridged dicobalt(II) bis-porphyrin dyad Co(P)-TA-(P)Co in its singly and doubly reduced form, but only weak interactions are seen between the two Co(PQ) units of the single bond biquinolalinyl-bridged dicobalt(II) bis-porphyrin dyad Co(PQ)-(QP)Co.
一系列钴（II）和钴（III）卟啉与融合的喹喔啉环在大环的一个或多个β，β'-吡咯单元中被合成并表征为其在非水介质中的电化学性质。在薄层电池中氧化或还原之前和期间，还测量了它们的紫外可见光谱。研究的喹喔啉卟啉表示为（PQ）Co，（QPQ）CoCl，（PQ（2））CoCl，Co（P）-TA-（P）Co和Co（PQ）-（QP）Co，其中 PQ = 5,10,15,20-四（3,5-二叔丁基苯基）-喹喔啉[2,3-b']卟啉的二阴离子，QPQ = 相应的线性双喹喔啉[2,3-b':12,13-b']卟啉的二阴离子，PQ（2）= 相应的角双喹喔啉[2,3-b':7,8-b']卟啉的二阴离子，（P）-TA-（P）= 两端融合有 5,10,15,20-四（3,5-二叔丁基苯基）卟啉的双卟啉的四阴离子。（P）Co和（P）CoCl也被表征，其中 P = 5,10,15,20-四（3,5-二叔丁基苯基）卟啉的二阴离子。尽管钴（II）喹喔啉卟啉的单电子还原导致具有混合钴（I）和卟啉π-阴离子自由基特征的产物，但每种化合物都可以在给定的氧化或还原电势下在其 Co（III），Co（II）和 Co（I）形式之间循环。随后在更负的电位下生成纯 Co（I）π-阴离子自由基物种。阐明了喹喔啉基团的位置和数量对每个电子转移的氧化还原电位和机制的影响，并与含有氧化还原活性和氧化还原非活性中心金属离子的结构相似的化合物进行了比较。令人惊讶的是，大环中环喹喔啉基团的位置和数量对 Co（II）→Co（III）或 Co（III）→Co（II）过程的氧化还原电位几乎没有或没有影响，但对于其他电子转移反应则不是如此，在这些反应中，检查过的化合物之间存在显著差异。在其单和双还原形式的横向桥接双钴（II）双卟啉偶联 Co（P）-TA-（P）Co中，两个卟啉大环之间也观察到显著的相互作用，但在单键双喹喔啉桥接的双钴（II）双卟啉偶联 Co（PQ）-（QP）Co 中仅观察到两个 Co（PQ）单元之间的弱相互作用。
