Fukuzumi Shunichi, Ohkubo Kei, Zhu Weihua, Sintic Maxine, Khoury Tony, Sintic Paul J, E Wenbo, Ou Zhongping, Crossley Maxwell J, Kadish Karl M
Department of Material and Life Science, Graduate School of Engineering, Osaka University, SORST, Japan Science and Technology Agency, Suita, Osaka 565-0871, Japan.
J Am Chem Soc. 2008 Jul 23;130(29):9451-8. doi: 10.1021/ja801318b. Epub 2008 Jun 28.
The metal-centered and macrocycle-centered electron-transfer oxidations and reductions of silver(II) porphyrins were characterized in nonaqueous media by electrochemistry, UV-vis spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The investigated compounds are {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrinato}silver(II), {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b']porphyrinato}silver(II), {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b':7,8-b'']porphyrinato}silver(II), and {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b':12,13-b'']porphyrinato}silver(II). The first one-electron oxidation and first one-electron reduction both occur at the metal center to produce stable compounds with Ag(III) or Ag(I) metal oxidation states, irrespective of the type of porphyrin ligand. The electrochemical HOMO-LUMO gap, determined by the difference in the first oxidation and first reduction potentials, decreases by introduction of quinoxaline groups fused to the Ag(II) porphyrin macrocycle. This provides a unique androgynous character to Ag(II) quinoxalinoporphyrins that enables them to act as both good electron donors and good electron acceptors, something not previously observed in other metalloporphyrin complexes. The second one-electron oxidation and second one-electron reduction of the compounds both occur at the porphyrin macrocycle to produce Ag(III) porphyrin pi-radical cations and Ag(I) porphyrin pi-radical anions, respectively. The macrocycle-centered oxidation potentials of each quinoxalinoporphyrin are shifted in a negative direction, while the macrocycle-centered reduction potentials are shifted in a positive direction as compared to the same electrode reactions of the porphyrin without the fused quinoxaline ring(s). Both potential shifts are due to a stabilization of the radical cations and radical anions by pi-extension of the porphyrin macrocycle after fusion of one or two quinoxaline moieties at the beta-pyrrolic positions of the macrocycle. Introduction of quinoxaline groups fused to the Ag(II) porphyrin macrocycle provides a unique androgynous character to Ag(II) quinoxalinoporphyrins that enables them to act as both good electron donors and good electron acceptors.
通过电化学、紫外-可见光谱电化学、电子顺磁共振光谱和密度泛函理论计算，对非水介质中银（II）卟啉的以金属为中心和以大环为中心的电子转移氧化还原过程进行了表征。所研究的化合物有{5,10,15,20-四（3,5-二叔丁基苯基）卟啉合}银（II）、{5,10,15,20-四（3,5-二叔丁基苯基）喹喔啉并[2,3-b']卟啉合}银（II）、{5,10,15,20-四（3,5-二叔丁基苯基）双喹喔啉并[2,3-b':7,8-b'']卟啉合}银（II）和{5,10,15,20-四（3,5-二叔丁基苯基）双喹喔啉并[2,3-b':12,13-b'']卟啉合}银（II）。第一个单电子氧化和第一个单电子还原均发生在金属中心，生成具有Ag(III)或Ag(I)金属氧化态的稳定化合物，与卟啉配体的类型无关。由第一个氧化电位和第一个还原电位之差确定的电化学HOMO-LUMO能隙，通过引入与Ag(II)卟啉大环稠合的喹喔啉基团而减小。这赋予了Ag(II)喹喔啉卟啉独特的两性特征，使其既能作为良好的电子供体，又能作为良好的电子受体，这在其他金属卟啉配合物中未曾观察到。这些化合物的第二个单电子氧化和第二个单电子还原均发生在卟啉大环上，分别生成Ag(III)卟啉π-自由基阳离子和Ag(I)卟啉π-自由基阴离子。与没有稠合喹喔啉环的卟啉的相同电极反应相比，每种喹喔啉卟啉的以大环为中心的氧化电位向负方向移动，而以大环为中心的还原电位向正方向移动。这两种电位移动都是由于在大环的β-吡咯位置稠合一个或两个喹喔啉部分后，卟啉大环的π-扩展使自由基阳离子和自由基阴离子得以稳定。引入与Ag(II)卟啉大环稠合的喹喔啉基团赋予了Ag(II)喹喔啉卟啉独特的两性特征，使其既能作为良好的电子供体，又能作为良好的电子受体。
