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Reactions of mer(exo)‐ and mer(endo)‐[Co(dien)(dapo)X]2+ Isomers (X=OH, Cl, ONO2, N3)

Rebecca J. Browne, David A. Buckingham, Charles R. Clark, J.A. McKeon, W.G. Jackson

Helvetica Chimica Acta, 2003

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Abstract

Abstract Properties indirectly determined, or alluded to, in previous publications on the titled isomers have been measured, and the results generally support the earlier conclusions. Thus, the common five‐coordinate intermediate generated in the OH−‐catalyzed hydrolysis of exo‐ and endo‐[Co(dien)(dapo)X]2+ (X=Cl, ONO2) has the same properties as that generated in the rapid spontaneous loss of OH− from exo‐ and endo‐[Co(dien)(dapo)OH]2+ (40±2% endo‐OH, 60±2% exo‐OH) and an unusually large capacity for capturing (R=[CoN3]/[CoOH][]=1.3; exo‐[CoN3]/endo‐[CoN3]=2.1±0.1). Solvent exchange for spontaneous loss of OH− from exo‐[Co(dien)(dapo)OH]2+ has been measured at 0.04 s−1 (k1, 0.50M NaClO4, 25°) from which similar loss from the endo‐OH isomer may be calculated as 0.24 s−1 (k2). The OH−‐catalyzed reactions of exo‐ and endo‐[Co(dien)(dapo)N3]2+ result in both hydrolysis of coordinated via an OH−‐limiting process =153 M−1 s−1; =295 M−1 s−1; KH=1.3±0.1 M−1; 0.50M NaClO4, 25.0°) and direct epimerization between the two reactants =33 M−1 s−1; =110 M−1 s−1; 1.0M NaClO4, 25.0°). Comparisons are made with other rapidly reacting CoIII‐acido systems.

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