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Reactions of mer ( exo )‐ and mer ( endo )‐[Co(dien)(dapo)X] 2+ Isomers (X=OH, Cl, ONO 2 , N 3 )
Author(s) -
Browne Rebecca J.,
Buckingham David A.,
Clark Charles R.,
McKeon Josephine A.,
Jackson W. Gregory
Publication year - 2003
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200390004
Subject(s) - chemistry , hydrolysis , limiting , medicinal chemistry , solvent , stereochemistry , catalysis , crystallography , organic chemistry , mechanical engineering , engineering
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, ONO 2 ) 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=[CoN 3 ]/[CoOH][]=1.3; exo ‐[CoN 3 ]/ endo ‐[CoN 3 ]=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 ( k 1 , 0.50 M NaClO 4 , 25°) from which similar loss from the endo ‐OH isomer may be calculated as 0.24 s −1 ( k 2 ). The OH − ‐catalyzed reactions of exo ‐ and endo ‐[Co(dien)(dapo)N 3 ] 2+ result in both hydrolysis of coordinated via an OH − ‐limiting process =153 M −1 s −1 ; =295 M −1 s −1 ; K H =1.3±0.1 M −1 ; 0.50 M NaClO 4 , 25.0°) and direct epimerization between the two reactants =33 M −1 s −1 ; =110 M −1 s −1 ; 1.0 M NaClO 4 , 25.0°). Comparisons are made with other rapidly reacting Co III ‐acido systems.