Synthesis and base hydrolysis kinetics of the nitrile complexes [Co(tetren)NCR]3+ (R=Me, Ph and p-MeOC6 H4) and the synthesis and kinetics of formation of the tetrazolato complexes [Co(tetren)N4R]2+ (R=Me and Ph; tetren=1,11-diamino-3,6,9-triazaundecane) by reaction with azide ion

Abstract

The N-bonded nitrile complexes αα-[Co(tetren)NCR]3+ (R=Me, Ph, p-MeOC6 H4) have been prepared by the reaction of αα-[Co(tetren)OH2]3+ with the corresponding nitrile. The kinetics of base hydrolysis have been studied by pH-stat methods. The reactions involve an SN1CB displacement of the nitrile to give the hydroxopentamine; nucleophilic attack at the nitrile carbon to give the corresponding carboxamido complex does not occur. NaN3 reacts with the nitrile complexes in slightly acidic solution (pH ca. 5.7) to give the tetrazolato complexes [Co(tetren)N4 R]2+ (R=Me, Ph) which have been characterised. The reaction of azide ion with αα-[Co(tetren)NCMe]3+ has been studied kinetically. The reaction is biphasic involving the initial rapid formation of the N1-bonded (5-methyltetrazolato) pentaminecobalt(III) complex with k=2×10−2dm3 mol−1s−1 at 25°C followed by the slow isomerisation to the N2-bonded complex with k=3.5×10−5s−1 at pH 5.7.