ic401232g_si_001.pdf (1.17 MB)
Synthesis and Electrochemical Studies of Cobalt(III) Monohydride Complexes Containing Pendant Amines
journal contribution
posted on 2016-02-18, 23:24 authored by Eric S. Wiedner, John A. S. Roberts, William G. Dougherty, W. Scott Kassel, Daniel L. DuBois, R. Morris BullockTwo new tetraphosphine ligands, PnC‑PPh22NPh2 (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
[CoII(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 [HCoIII(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
[CoI(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.
History
Usage metrics
Categories
Keywords
cyclic voltammetryHCoIbulk electrolysis conditionsvoltammetric conditionsform 2 equivH 2HCoIItetraphosphine ligandsH 2.KC 8CHH 2 formationElectrochemical StudiesCoI complexesmonometallic processHCoIIIErCrEr reduction mechanismelectrocatalytic conditionscobalt hydrideacetonitrile dissociationbimetallic route1 equivcobalt hydride complexes
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC