NDLI: Syn–anti conformational switching in an ethane-bridged Co(II)bisporphyrin induced by external stimuli: effects of inter-macrocyclic interactions, axial ligation and chemical and electrochemical oxidations

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Dey, Soumyajit Rath, Sankar Prasad
Description	Author Affiliation: Dey S ( Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India. sprath@iitk.ac.in.)
Abstract	The syn–anti conformational switching has been demonstrated in the ethane-bridged dicobalt(II)bisporphyrin which is present in the syn-form only. The addition of either perylene or axial ligands to $Co^{II}(bisporphyrin)$ completely transforms the syn form into the anti because of strong π–π interaction and axial coordination, respectively. The complex undergoes four 1e-oxidations in $CH_{2}Cl_{2}$ which are indicative of strong through space interactions between the two cofacial Co-porphyrins at 295 K. The first oxidation is a metal centered one and occurs at a potential much lower than that of the monomeric analog. However, the second oxidation, which is again metal centered, was at a significantly higher potential. The large difference between the first two oxidations, as observed here, is due to much stronger inter-porphyrin interactions. The step-wise oxidations have been performed both chemically and electro-chemically while the progress of the reactions was monitored by UV-visible and $^{1}H$ NMR spectroscopy. After 1e-oxidation, a very broad $^{1}H$ NMR signal results with increased difference between two meso resonances, which indicates that the two macrocycles are in the syn-form with lesser interplanar separation as also observed by DFT. However, 2e-oxidation results in the stabilization of the anti form. The addition of axial ligands to $Co^{II}(bisporphyrin)$ also completely transforms the syn form into the anti form. While additions of THF and $I_{2}/I^{−}$ both result in the formation of five-coordinate complexes, Co(II) is oxidized to Co(III) in the case of the latter. However, additions of 1-methylimidazole, pyridine and pyrazine as axial ligands result in the formation of a six-coordinate complex in which Co(II) is spontaneously oxidized to Co(III) in air.
ISSN	14779226
Issue Number	5
Volume Number	43
e-ISSN	13645447
Journal	Dalton Trans.
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2014-02-07
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Ethane Chemistry Macrocyclic Compounds Porphyrins Crystallography, X-Ray Electrochemistry Molecular Conformation Oxidation-Reduction Perylene Journal Article Research Support, Non-U.S. Gov't
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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