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 Xray 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 ' -diplienyl-2,2 ' -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.