New silver imidazol-2-ylidene complexes with pendant N-β-chloroethyl and N-vinyl groups. Cl⋅⋅⋅N and C-H⋅⋅⋅Ag weak interactions

Abstract

A series of silver monoimidazol-2-ylidene chlorides and silver bisimidazol-2-ylidene tetraphenylborates, bearing pendant N-β-chloroethyl (-CHEt-CH2Cl; -CHMe-CHPhCl) and N-vinyl (-CEt = CH2; -CMe = CHPh) substituents were synthesized and their structure analysed by IR, mass spectra and NMR. Stereogenic carbon atoms give place to enantiomerically pure carbenes. Organized N-pendant groups provide steric protection and stabilization of the reactive carbenes sites. The bulky substituents acquired recurrent similar conformations that were attributed to the presence of non-classical Cl⋅⋅⋅N and C-H⋅⋅⋅Ag stabilizing interactions. The weak interactions Cl⋅⋅⋅N and C-H⋅⋅⋅Ag were deduced from the close atomic contacts and directionality the bonds in the X-ray diffraction analysis. DFT calculations of the optimised geometries, electrostatic potential, electron density distribution, critical points of the non-covalent weak bonds and critical points of the Laplacian function of the electrostatic potential confirmed the stabilizing character of the weak interaction. Crystals of di(1,3-bis[1′-chlorobutan-2′-yl]-imidazolium)-silver trichloride were isolated from a solution of (1,3-bis[(R)-1′-chlorobutan-2′-yl]-imidazol-2-ylidene)-silver chloride. As far as we know, this is a first example of this free D3h monomer of AgCl32− in the solid state.