Co-ordination chemistry of CuI with 1,3,5-tris[bis(pyridin-2-ylmethyl)aminomethyl]-2,4,6-triethylbenzene, a conformationally constrained trinucleating ligand

Abstract

The new ligand 1,3,5-tris[bis(pyridin-2-ylmethyl)aminomethyl]-2,4,6-triethylbenzene (L) was prepared from 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene (TriBr) and bis(pyridin-2-ylmethyl)amine. In the crystal state TriBr adopts a conformation with the substituents alternately pointing to opposite sides of the plane of the benzene ring. Compound L adopts a similar conformation. With its donor sets thus coming together on the same side of the benzene ring L can co-ordinate three copper(I) species in a defined and close proximity. This is illustrated by the crystal structures of L, [(CuI)₃L] and [(CuNCMe)₃L][PF₆]₃. The electrochemical interdependence of the copper centres in [(CuI)₃L] and [(CuBr)₃L] has been investigated by cyclic voltammetry. With weaker and harder terminal ligands such as acetonitrile the [Cu^I₃L]³⁺ species in CH₂Cl₂ are liable to oxidation by the solvent to give Cu^IICl⁺ species. In one such degradation product L co-ordinates besides an isolated Cu^I, a Cu^I and a Cu^II bridged by a single chloride. The Cu^II is further co-ordinated by an oxygen from a perchlorate anion. From the reaction of only two equivalents of [Cu(NCMe)₄]BF₄ with L a dinuclear compound was obtained, in which both copper atoms experience a distorted trigonal co-ordination from three pyridine nitrogen atoms each.