Tuning the Helicity of (2,2′-Bidipyrrinato)-nickel(II) Complexes

Summary.  The influence of the terminal substituents of 2,2′-bidipyrrin ligands on the geometrical and spectroscopic properties of the respective nickel(II) complexes was investigated. Helicity was found to be an intrinsic structural feature of all 2,2′-bidipyrrins studied to date, including a species with minimum helical overlap. Surprisingly, no changes became apparent upon increasing the size of the terminal substituent from methyl to 1,4-butadiyl. t-Butyl groups at the termini, however, were found to be sterically too demanding to allow the formation of stable nickel(II) complexes. Received October 5, 2001. Accepted (revised) November 14, 2001