Molecular and Electronic Structure of (2,2′-Bidipyrrinato)nickel(II) Complexes

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.