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 k_OH(dats) 3.6 × 10⁴ dm³ mol^-1 s^-1 and k_OH(datn) 2.85 × 10³ dm³ mol^-1 s^-1 at 25ºC 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.