Synthesis, structural characterization, and bonding analysis of two-coordinate copper(i) and silver(i) complexes of pyrrole-based bis(phosphinimine): new metal–pyrrole ring π-interactions

Abstract

The reaction between 2,5-bis(diphenylphosphinomethyl)pyrrole and Me₃SiN₃ gave the new pyrrole-based bis(phosphinimine) L1H in an excellent yield. L1H reacts with [CuCl(COD)]₂, AgBF₄, or AgOTf to give the corresponding two-coordinate mononuclear ionic complex formulated as [M{(L1H)-κ²N,N}]⁺[X]⁻ where M = Cu and Ag; X = [CuCl₂], BF₄ or OTf. Their single crystal X-ray diffraction studies confirmed the two-coordinate geometry formed by the chelate bonding mode of L1H. These 10-membered metalacycles exhibit planar chirality and were also characterized by spectroscopic methods. In addition, in all three structures, there exists a hitherto unknown π-interaction between the pyrrole ring atoms and metal, represented as η²-(C_α–N) in the copper(I) complex, and η³-(C_α–N–C_α′) in the silver(I) complexes. These weak interactions were supported by DFT calculations in terms of their electron densities, non-covalent interaction plots and the decrease in the aromaticity of the pyrrole ring.