Asymmetric copper complexes of stable mono-tert-butyl monobenzyl dithioether N2S2 ligands

Abstract

Attempts to form copper complexes of new N₂S₂ compounds, in which one sulfur donor is a thiolate and the other a thioether, have been made by protecting the potential thiolate through tert-butylation and benzylating the other. Whereas earlier work with symmetrical bis(tert-butylated thioethers) had shown that de-tert-butylation occurs upon co-ordination to copper, to yield the bis(thiolate) complex, this proves not to be the case with these asymmetric compounds. Thus, complexation of N-[2-(benzylsulfanyl)benzyl]-N′-[2-(tert-butylsulfanyl)benzylidene]ethane-1,2-diamine, L¹, and N-[2-(benzylsulfanyl)benzyl]-N′-{[2-(tert-butylsulfanyl)benzyl]ethane-1,2-diamine, L², leads to stable copper(I) complexes and in the case of L¹ a stable copper(II) complex as well. The copper(I) perchlorate complexes of L¹ and L² have been characterised by X-ray crystallography and both complex cations are found to have distorted-tetrahedral structures [CuN₂–CuS₂ dihedral angles of 74.05(9) and 73.5(2)°, respectively] in which the tert-butyl group is retained. The 2-cyanoethyl group has also been investigated as a protecting group for the thiolate moiety in N-[(2-benzylsulfanyl)benzyl]-N′-[2-(2-cyanoethylsulfanyl)benzylidene]-N′-methylethane-1,2-diamine, L³, which forms a stable complex with copper(II) but not with copper(I). Decyanoethylation of [CuL³]²⁺ could not be induced.