Preparation of a New Ligand Containing Disulfide and Imidazole Donor Groups. Structure of Dibromo[5-(l,2,5-dithiazepan-5-ylmethylene)-4-methyl-2-ethylimidazole]cadmium(II).¹¹³Cd and¹³C NMR Studies of Complex Formation

Received March 16, 1984 The title ligand (MAMI) was prepared by reaction of 2-ethyl-4-methylimidazole and diethanolamine under basic (pH 11) Mannich conditions and treatment of the resultant alcohol with thionyl chloride. The nitrogen mustard formed was derivatized with thiourea to afford a bis(isothiuronium) salt. Hydrolysis of this material to a dimercaptide could only be accomplished efficiently in the presence of transition-metal salts. Treatment of the isothiuronium salt with NiCl₂under basic conditions afforded an incompletely characterized derivative in which, by IR spectroscopy and C:N ratio, the ligand had been completely hydrolyzed to a dimercaptide. Oxidation of this material by I₂and extraction into HCC1₃afforded the title ligand. Changes in the¹3C NMR spectrum of MAMI in Me₂SO-d₆as a function of added Cd(NO₃)₂revealed the formation of a 1:1 complex with K(˜ 60 M^-1.The coordinated and free ligand are in fast exchange on the¹³C NMR scale, and the assessement of the groups involved in complex formation was unclear. However,¹¹³Cd NMR is consistent with coordination by the two N donors in MAMI. The 1:1 complex is in slow exchange on the¹¹³Cd NMR time scale. Crystalline complexes of MAMI with CdCl₂and CdBr₂were isolated. The CdBr₂complexwas investigated by X-ray methods. Crystal data: P2₁/n, a = 12.988 (4) Å, b = 10.899 (3)Å,c = 13.148 (3)Å, γ = 108.74 (2)°, Z = 4, R = 0.0235 for 1474 independent reflections.