Products of the reactions of sparteine-2-thione with CuBr2 in protic and aprotic solvents

Reactions of copper(II) bromide with racemic sparteine-2-thione (SSp) in a 1:1 M ratio yielded two new complexes, whose structures depend on the solvent used. In acetonitrile, the reaction product is a sulfur-bridged dinuclear CuBr₂(μ-SSp)]₂ complex (1) in which sparteine-2-thione acts as a bridging S-ligand, while in methanol it is a CuBr₂ complex (2) with sparteine deprived of the A-ring. Compound 1 crystallizes as an acetonitrile solvate in a 1:2 ratio and constitutes one of a few Cu(II) doubly bridged heterocyclic thionato complexes. The disorder of the C/D bisquinolizidine fragment in the crystal of 1 reflects the ease of the conversion from the common trans boat-chair to the unprecedented cis chair-boat stereoisomer. Obtained in methanol, the sparteine surrogate (Sp(surr)), is equally effective as a chelating ligand as sparteine and its isomers, and thus can be used as an alternative diamine ligand in metal complexation. Metal coordination with Sp(surr) brings the diamine nitrogens much closer together than in any other sparteine metal complexes.