Molecular and electronic structure of (2,2 '-bidipyrrinato)nickel(II) complexes

Nickel complexes of eight differently substituted 2,2 ' -bidipyrrins have b een prepared and fully characterized. The Xray analyses of three of these c omplexes revealed helical chiral molecules. Despite the tetrahedral deviati on from the square-planar coordination geometry at the metal centres, all c ompounds 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) n ickel, a separation into the enantiomers by chiral MPLC could be achieved, and the first CD spectra of enantiomerically pure tetrapyrrole helicates ar e reported. An electrochemical study of the new complexes allowed a first i nsight into the electronic structure of (2,2 ' -bidipyrrinato)nickel(II), d isclosing a rather high energy HOMO and metal-ligand interaction similar to that observed in metalloporphyrins.