Synthesis and electrochemical studies of cobalt(III) monohydride complexes containing pendant amines

Eric S. Wiedner, John A.S. Roberts, William G. Dougherty, W. Scott Kassel, Daniel L. Dubois, R. Morris Bullock

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52 Citations (Scopus)


Two new tetraphosphine ligands, P nC-PPh2 2N Ph2 (1,5-diphenyl-3,7-bis((diphenylphosphino)alkyl)-1,5- diaza-3,7-diphosphacyclooctane; alkyl = (CH2)2, n = 2 (L2); (CH2)3, n = 3 (L3)), have been synthesized. Coordination of these ligands to cobalt affords the complexes [Co II(L2)(CH3CN)]2+ and [CoII(L3) (CH3CN)]2+, which are reduced by KC8 to afford [CoI(L2)(CH3CN)]+ and [CoI(L3) (CH3CN)]+. Protonation of the CoI complexes affords [HCoIII(L2)(CH3CN)]2+ and [HCo III(L3)(CH3CN)]2+. The cyclic voltammetry of [HCoIII(L2)(CH3CN)]2+, analyzed using digital simulation, is consistent with an ErCrEr reduction mechanism involving reversible acetonitrile dissociation from [HCoII(L2)(CH3CN)]+ and resulting in formation of HCoI(L2). Reduction of HCoIII also results in cleavage of the H-Co bond from HCoII or HCoI, leading to formation of the CoI complex [CoI(L2)(CH3CN)] +. Under voltammetric conditions, the reduced cobalt hydride reacts with a protic solvent impurity to generate H2 in a monometallic process involving two electrons per cobalt. In contrast, under bulk electrolysis conditions, H2 formation requires only one reducing equivalent per [HCoIII(L2)(CH3CN)]2+, indicating a bimetallic route wherein two cobalt hydride complexes react to form 2 equiv of [Co I(L2)(CH3CN)]+ and 1 equiv of H2. These results indicate that both HCoII and HCoI can be formed under electrocatalytic conditions and should be considered as potential catalytic intermediates.

Original languageEnglish
Pages (from-to)9975-9988
Number of pages14
JournalInorganic Chemistry
Issue number17
Publication statusPublished - Sep 2 2013

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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