Synthesis and Reactivity of Pyridine N-Oxide Complexes of Cobalt(III)

William L. Purcell

Research output: Contribution to journalArticle

9 Scopus citations

Abstract

The syntheses of four new pentaamminecobalt(III) complexes with pyridine N-oxide, 4-methylpyridine N-oxide, 2-cyanopyridine N-oxide, and 4-cyanopyridine N-oxide are described. The first two ligands bond through the oxygen, while the latter two ligands are bonded via the nitrile group nitrogen. Reaction kinetics have been used to investigate the reactivity of these complexes. The rate constant for aquation of the pyridine N-oxide complex at 25°C is 2.51 × 10-6 s-1. Chromium(II) reduction of the pyridine N-oxide complex is an inner-sphere process with a rate constant at 25°C of 0.371 M-1 s-1, an activation enthalpy of 3.75 ± 1.2 kcal mol-1, and an activation entropy of -48 ± 4 cal K-1 mol-1. The 4-cyanopyridine N-oxide complex undergoes facile base hydrolysis of the nitrile function to a bound amide. The rate constant for this process at 25°C is 4030 ± 125 M-1 s-1. The 2-cyanopyridine N-oxide complex exhibits this same nitrile group conversion even in acidic solution, where water is shown to function as a competitive attacking nucleophile.

Original languageEnglish (US)
Pages (from-to)2312-2315
Number of pages4
JournalInorganic Chemistry
Volume28
Issue number12
DOIs
StatePublished - Jun 1 1989

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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