School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China.
Inorg Chem. 2011 Dec 19;50(24):12802-9. doi: 10.1021/ic2019567. Epub 2011 Nov 9.
The electrochemistry of gold(III) mono- and bis-quinoxalinoporphyrins was examined in CH(2)Cl(2) or PhCN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) before and after the addition of trifluoroacetic acid to solution. The investigated porphyrins are represented as Au(PQ)PF(6) and Au(QPQ)PF(6), where P is the dianion of the 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin and Q is a quinoxaline group fused to a β,β'-pyrrolic position of the porphyrin macrocycle; in Au(QPQ)PF(6) there is a linear arrangement where the quinoxalines are fused to pyrrolic positions that are opposite each other. The porphyrin without the fused quinoxaline groups, Au(P)PF(6), was also investigated under the same solution conditions. In the absence of acid, all three gold(III) porphyrins undergo a single reversible Au(III)/Au(II) process leading to the formation of a Au(II) porphyrin which can be further reduced at more negative potentials to give stepwise the Au(II) porphyrin π-anion radical and dianion, respectively. However, in the presence of acid, the initial Au(III)/Au(II) processes of Au(PQ)PF(6) and Au(QPQ)PF(6) are followed by an internal electron transfer and protonation to regenerate new Au(III) porphyrins assigned as Au(III)(PQH)(+) and Au(III)(QPQH)(+). Both protonated gold(III) quinoxalinoporphyrins then undergo a second Au(III)/Au(II) process at more negative potentials. The electrogenerated monoprotonated monoquinoxalinoporphyrin, Au(II)(PQH), is then further reduced to its π-anion radical and dianion forms, but this is not the case for the monoprotonated bis-quinoxalinoporphyrin, Au(II)(QPQH), which accepts a second proton and is rapidly converted to Au(III)(HQPQH)(+) before undergoing a third Au(III)/Au(II) process to produce Au(II)(HQPQH) as a final product. Thus, Au(P)PF(6) undergoes one metal-centered reduction while Au(PQ)PF(6) and Au(QPQ)PF(6) exhibit two and three Au(III)/Au(II) processes, respectively. These unusual multistep sequential Au(III)/Au(II) processes were monitored by thin-layer spectroelectrochemistry and a reduction/oxidation mechanism for Au(PQ)PF(6) and Au(QPQ)PF(6) in acidic media is proposed.
在添加三氟乙酸前后，研究了金（III）单-和双-喹喔啉卟啉在 CH(2)Cl(2)或 PhCN 中的电化学性质，其中含有 0.1 M 四丁基高氯酸铵 (TBAP)。研究的卟啉表示为 Au(PQ)PF(6)和 Au(QPQ)PF(6)，其中 P 是 5,10,15,20-四（3,5-二叔丁基苯基）卟啉的二阴离子，Q 是喹喔啉基团，融合到卟啉大环的β，β'-吡咯位置；在 Au(QPQ)PF(6)中，喹喔啉基团融合到彼此相对的吡咯位置，形成线性排列。在相同的溶液条件下，还研究了没有融合的喹喔啉基团的金（III）卟啉 Au(P)PF(6)。在没有酸的情况下，所有三种金（III）卟啉都经历了一个单一的可逆 Au(III)/Au(II)过程，导致形成 Au(II)卟啉，该卟啉可以在更负的电位下进一步还原，分别依次生成 Au(II)卟啉π-阴离子自由基和二阴离子。然而，在有酸存在的情况下，Au(PQ)PF(6)和 Au(QPQ)PF(6)的初始 Au(III)/Au(II)过程之后是内部电子转移和质子化，以再生新的 Au(III)卟啉，指定为 Au(III)(PQH)(+)和 Au(III)(QPQH)(+)。两个质子化的金（III）喹喔啉卟啉随后在更负的电位下经历第二个 Au(III)/Au(II)过程。然后，电生成的单质子化的单喹喔啉卟啉 Au(II)(PQH)进一步还原为其π-阴离子自由基和二阴离子形式，但单质子化的双喹喔啉卟啉 Au(II)(QPQH)则不是这样，它接受第二个质子，然后迅速转化为 Au(III)(HQPQH)(+)，然后再经历第三个 Au(III)/Au(II)过程，生成最终产物 Au(II)(HQPQH)。因此，Au(P)PF(6)经历了一个金属中心还原，而 Au(PQ)PF(6)和 Au(QPQ)PF(6)分别显示了两个和三个 Au(III)/Au(II)过程。通过薄层光谱电化学监测了这些不寻常的多步顺序的 Au(III)/Au(II)过程，并提出了在酸性介质中 Au(PQ)PF(6)和 Au(QPQ)PF(6)的还原/氧化机制。
