Demonstration of remote steric differentiation of cis/transalkene coordination in copper(i) complexes of aryl-substituted bis(2-pyridyl)amine

Abstract

Complexes of the type [Cu(R-dpa)(η²-olefin)]BF₄ (R = Mes and 2-ⁱPrC₆H₄) for cis- and trans- isomers of 3-octene, as well as those for cis- and trans-4-octene (R = 2-ⁱPrC₆H₄) have been prepared and characterized by ¹H and ¹³C NMR, FTIR, and TGA. The crystal structure of [Cu(Mes-dpa)(η²-trans-3-octene)]BF₄ (2) has been determined via X-ray crystallography. The asymmetric unit in the crystal lattice of 2 contains two unique conformations of the complex cation related by a pseudo center of symmetry, which differ primarily in the orientation of the olefin with respect to the rest of the molecule. The ¹H and ¹³C NMR spectra of [Cu(Ar-dpa)(η²-olefin)]BF₄ exhibit olefin resonances shifted upfield with respect to free olefin. The difference in Δδ(¹³C) relative magnitudes between cis- and trans- complexes, i.e., the binding, correlates with the degree of substitution at the amine nitrogen. The identity of the remote ligand substituent (Ar) controls the differentiation of binding between cis and trans isomers as a consequence of increased folding of the Ar-dpa ligand along the Cu⋯N axis.