Di-μ-hydroxo Bridge Cleavage Reactions between [Co(nta)(μ-OH)]2 2– and various N,N-Bidentate Ligands

The cleavage of the di-μ-hydroxo bridges of [Co(nta)(μ-OH)]2 2– by en and N,N-Et2en (en = ethylenediamine and N,N-Et2en = N,N-diethylethylene-diamine) has been investigated. [Co(nta)(μ-OH)]2 2– equilibrates rapidly in aqueous basic solutions, yielding a mono-μ-hydroxo-bridged Co(III) complex [pKOH = 3.3(1)] and both these species react with the incoming ligand to form different ion associated species. These, in turn, react to form presumably a ligand-substituted, mono-bridged species, [(nta)(OH)Co-μ-OH-Co(nta)(L-L)]2–, which upon ring-closure rapidly formthe products.Values for k2, the preferred pathway for these reactions, vary between 1.42(4) × 10–2 s–1 (en) and 3.2(1) × 10–3 s–1 (N,N-Et2en) at 25.0°C, μ = 0.2 M (NaClO4).KEY WORDS: Bridge cleavage, cobalt(III), kinetics, mechanism, nitrilotriacetate