Branched cyclononane macrocycles with pentaamine and tetraamine-thioether donors. Preparation and base hydrolysis of chlorocobalt(III) complexes

Abstract

Synthetic routes to the resolved unsymmetrical (u) isomers of [Co(dats)Cl] (ClO4)2 [dats = 4,7-bis-(2-aminoethyl)-1-thia-4,7-diazacyclononane] and [Co(datn)Cl] (ClO4)2 [datn = 1,4-bis(2-aminoethyl)-1,4,7-triazacyclononane] are reported. The new macrocyclic ligand 1-thia-4,7-diazacyclononane (tasn) was synthesized during the former preparation, and the cis-[Co(tasn)2] (ClO4)3 complex prepared. Base hydrolysis of each chlorocobalt(III) complex proceeds with two consecutive steps. The first reaction in each case is chloride hydrolysis, with kOH(dats) 3.6 × 104 dm3 mol-1 s-1 and kOH(datn) 2.85 × 103 dm3 mol-1 s-1 at 25�C and 10.1 M. The second reaction for the dats complex is a base-catalysed dissociation of the thioether to the cis-[Co(dats)(OH)2]+ complex, characterized by 13C n.m.r. experiments, and occurring approximately 20 times slower than chloride hydrolysis. However, the datn complex undergoes a base-catalysed terminal ring opening to the cis-[Co(datn)- (OH)2]+ complex at a rate approximately 30 times slower than chloride hydrolysis.