The chemistry of vitamin B12. Part 22. Steric effects in the co-ordination of amines by cobalt(III) corrinoids

David A. Baldwin, Eric Betterton, John M. Pratt

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The following equilibrium constants (given as log10K/dm3 mol-1) have been determined by spectrophotometry for the substitution in cobalt(III) corrinoids of co-ordinated H2O by various amines B with different trans ligands X in aqueous solution (I = 0.2 mol dm-3) at 25 °C: X = 5,6-dimethylbenzimidazole (dbzm), B = NH2Me (ca. 6), NHMe2 (3.4), NMe3 (≤1), NH2Et (5.3), NH2Pri and NH2But (both ≤1); X = CN-, B = NH2Me (3.4), NHMe2(2.0), NMe3(ca. 0); X = vinyl, B = NH3 (-0.06), NH2Me (+0.04), NHMe2 and NMe3 (both ≤ - 1). These results show that steric effects increase in importance as the donor power of the trans ligand X decreases (from vinyl through CN- to dbzm) and that significant steric effects are caused by substitution on the β (C) atom as well as on the α (N) atom.

Original languageEnglish (US)
Pages (from-to)2217-2222
Number of pages6
JournalJournal of the Chemical Society, Dalton Transactions
Issue number10
Publication statusPublished - 1983
Externally publishedYes


ASJC Scopus subject areas

  • Chemistry(all)

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