Co-ordination chemistry of Cu-1 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 I, can co-ordinate three copper(I) species in a defined and close proximity. This is illustrated by the crystal structures of L, [(CuI)(3)L] and [(CuNCMe)(3)L][PF6](3). The electrochemical interdependence of the copper centres in [(CuI)(3)L] and [(CuBr)(3)L] has been investigated by cyclic voltammetry. With weaker and harder terminal ligands such as acetonitrile the [(Cu3L)-L-I](3+) species in CH2Cl2 are liable to oxidation by the solvent to give (CuCl+)-Cl-II 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.