Reduction of Pentaamminecobalt(III) Complexes of Aromatic Nitriles by Chromium(II)

Robert J. Balahura, W. L. Purcell

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8 Scopus citations


The reductions of the pentaamminecobalt(III) complexes of 3-formylbenzonitrile, 4-formylbenzonitrile, furanacrylonitrile, cinnamonitrile, and acetoxybenzonitrile by chromium(II) have been studied. The reductions all follow the rate law -(d ln (Co3+)/dt) = k[Cr2+]. The 3-formyl complex has a specific rate constant of 77 ± 8 M-1 s-1 at 25° and μ = 0.5 M. The 4-formyl derivative is reduced at a rate of 2.5 ± 0.2 × 105 M-1 s-1 at 25° and μ = 0.5 M. In the latter system the reductant attacks the remote formyl carbonyl oxygen producing the intermediate A3 which has been detected spectrally. The (NH3)5Co3+ complex of 4-formylbenzonitrile is 30% hydrated in aqueous solution, and the dehydration reaction has also been studied. The furanacrylonitrile, cinnamonitrile, and acetoxybenzonitrile complexes are reduced by an outer-sphere process with rate constants 0.020 ± 0.002, 0.022 ± 0.004, and 0.021 ± 0.003 M-1 s-1 at 25° and μ = 0.5 M, respectively. The results are discussed in terms of the reducibility of the ligands and the stabilities of the precursor complexes. Comparison to analogous carboxylato complexes is also made.

Original languageEnglish (US)
Pages (from-to)4457-4462
Number of pages6
JournalJournal of the American Chemical Society
Issue number15
StatePublished - Jul 1 1976

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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