Investigations on organotin compounds XX. The existence of complexes with five-co-ordinated tin in solutions

Abstract

N-Tributylstannylimidazole forms complexes with basic ligands (B) in which the tin atom becomes pentacovalently bound. In the general structure Bu3SnImB, B may be another molecule of Bu3SnIm, which gives rise to the formation of a co-ordination polymer. In inert solvents this polymer causes the viscosity to rise sharply with increasing concentration. The efficiency of competing complexing agents can be evaluated by following the decrease of the viscosity of solutions of Bu3SnIm upon addition of these agents. Results are (i) that association of Bu3SnIm occurs more readily than association of imidazole over hydrogen bridges, (ii) that Bu3SnIm is complexed preferentially by either second row atoms (P, S) or by unsaturated ligands. A possible explanation, involving stabilization of the complexes by back donation of dπ-electrons from the tin atom towards the ligands, is discussed.