Nickel complexes of eight differently substituted 2,2′‐bidipyrrins have been prepared and fully characterized. The X‐ray analyses of three of these complexes revealed helical chiral molecules. Despite the tetrahedral deviation from the square‐planar coordination geometry at the metal centres, all compounds were found to be diamagnetic in nature. For (3,3′,4,4′,8,8′,9,9′‐octaethyl‐10,10′‐dimethyl‐6,6′‐diphenyl2,2′‐bidipyrrinato)nickel, a separation into the enantiomers by chiral MPLC could be achieved, and the first CD spectra of enantiomerically pure tetrapyrrole helicates are reported. An electrochemical study of the new complexes allowed a first insight into the electronic structure of (2,2′‐bidipyrrinato)nickel(II), disclosing a rather high energy HOMO and metal−ligand interaction similar to that observed in metalloporphyrins.
In the present work the effect of spiroconjugation on the electronic spectrum of the recently synthesized metal complex hexadecaethylspirodicorrolato-dinickel(II) (5) (the corrole units in 5 are isoforms) is investigated. To have a suitable reference compound at our disposal, tetraethylhexamethylisocorrolato nickel(II) (7) has been prepared. On comparing the electronic spectra of this reference compound and the spiro-complex, bathochromic shifts of all absorption bands in the NIR/Vis-region are observed for the latter as well as marked changes in the spectral intensities. A detailed analysis of the spectra supported by semiempirical calculations reveals that at least part of the observed changes can be unambiguously attributed to the spiro effect. This effect is further affirmed by electrochemically measured redox potentials.
This work reports on electrochemical investigations of ''figure-eight''-shaped cyclooctapyrrolic macrocycles (octaphyrins) 1−3 and of some of their mono-and dinuclear transition metal complexes. The octaphyrins 1−3 differ mainly in the size of the main conjugation pathway, which involves either 4n π-electrons for 1 and 3, or (4n + 2) π-electrons for 2. All species studied undergo six redox steps, namely two reductions and four oxidations. The two reductions and the first three oxidations are reversible one-electron transfers. The fourth oxidation is either reversible, or irreversible due to a subsequent chemical reaction. Depending on the complex studied, the third and fourth oxidations occur either at similar potentials, so that a global two-electron step is observed, or at distinct potentials, leading to two well-separated signals.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.