Cobalt complexes containing pendant amines in the second coordination sphere as electrocatalysts for H2 production

Ming Fang, Eric Wiedner, William G. Dougherty, W. Scott Kassel, Tianbiao Liu, Daniel L DuBois, R Morris Bullock

Research output: Contribution to journalArticle

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Abstract

A series of heteroleptic 17e cobalt complexes, [CpCoII(PtBu 2NPh 2)](BF4), [CpC6F5CoII(PtBu 2NPh 2)](BF4), and [CpC5F4NCoII(PtBu 2NPh 2)](BF4) (where PtBu 2NPh 2 = 1,5-diphenyl-3,7-di-tert-butyl-1,5-diaza-3,7-diphosphacyclooctane, CpC6F5 = C5H4(C6F5), and CpC5F4N = C5H4(C5F4N)) were synthesized, and the structures of all three were determined by X-ray crystallography. Electrochemical studies showed that the CoIII/II couple of [CpC5F4NCoII(PtBu 2NPh 2)]+ appears 250 mV positive of the CoIII/II couple of [CpCoII(PtBu 2NPh 2)]+ as a result of the strongly electron withdrawing perfluoropyridyl substituent on the Cp ring. Reduction of these paramagnetic CoII complexes by KC8 led to the diamagnetic 18e complexes CpCoI(PtBu 2NPh 2), CpC6F5CoI(PtBu 2NPh 2), and CpC5F4NCoI(PtBu 2NPh 2), which were also characterized by crystallography. Protonation of these neutral CoI complexes led to the CoIII hydrides [CpCoIII(PtBu 2NPh 2)H](BF4), [CpC6F5CoIII(PtBu 2NPh 2)H](BF4), and [CpC5F4NCoIII(PtBu 2NPh 2)H](BF4), and crystal structures of each of these cobalt hydrides were determined. The cobalt complex with the most electron withdrawing Cp ligand, [CpC5F4NCoII(PtBu 2NPh 2)]+, is an electrocatalyst for production of H2 using [p-MeOC6H4NH3][BF4] (pKa MeCN = 11.86), with a turnover frequency of 350 s-1 and an overpotential of 0.86 V at Ecat/2. A pKa value of 15.6 was measured in CH3CN for [CpC5F4NCoIII(PtBu 2NPh 2)H], which was used in conjunction with electrochemical measurements to obtain thermodynamic data for cleavage of the Co-H bond.

Original languageEnglish
Pages (from-to)5820-5833
Number of pages14
JournalOrganometallics
Volume33
Issue number20
DOIs
Publication statusPublished - Oct 27 2014

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electrocatalysts
Electrocatalysts
Cobalt
Amines
amines
cobalt
Hydrides
crystallography
hydrides
Crystallography
Electrons
Protonation
X ray crystallography
cleavage
electrons
Crystal structure
Thermodynamics
Ligands
Hydrogen
thermodynamics

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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Cobalt complexes containing pendant amines in the second coordination sphere as electrocatalysts for H2 production. / Fang, Ming; Wiedner, Eric; Dougherty, William G.; Kassel, W. Scott; Liu, Tianbiao; DuBois, Daniel L; Bullock, R Morris.

In: Organometallics, Vol. 33, No. 20, 27.10.2014, p. 5820-5833.

Research output: Contribution to journalArticle

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title = "Cobalt complexes containing pendant amines in the second coordination sphere as electrocatalysts for H2 production",
abstract = "A series of heteroleptic 17e cobalt complexes, [CpCoII(PtBu 2NPh 2)](BF4), [CpC6F5CoII(PtBu 2NPh 2)](BF4), and [CpC5F4NCoII(PtBu 2NPh 2)](BF4) (where PtBu 2NPh 2 = 1,5-diphenyl-3,7-di-tert-butyl-1,5-diaza-3,7-diphosphacyclooctane, CpC6F5 = C5H4(C6F5), and CpC5F4N = C5H4(C5F4N)) were synthesized, and the structures of all three were determined by X-ray crystallography. Electrochemical studies showed that the CoIII/II couple of [CpC5F4NCoII(PtBu 2NPh 2)]+ appears 250 mV positive of the CoIII/II couple of [CpCoII(PtBu 2NPh 2)]+ as a result of the strongly electron withdrawing perfluoropyridyl substituent on the Cp ring. Reduction of these paramagnetic CoII complexes by KC8 led to the diamagnetic 18e complexes CpCoI(PtBu 2NPh 2), CpC6F5CoI(PtBu 2NPh 2), and CpC5F4NCoI(PtBu 2NPh 2), which were also characterized by crystallography. Protonation of these neutral CoI complexes led to the CoIII hydrides [CpCoIII(PtBu 2NPh 2)H](BF4), [CpC6F5CoIII(PtBu 2NPh 2)H](BF4), and [CpC5F4NCoIII(PtBu 2NPh 2)H](BF4), and crystal structures of each of these cobalt hydrides were determined. The cobalt complex with the most electron withdrawing Cp ligand, [CpC5F4NCoII(PtBu 2NPh 2)]+, is an electrocatalyst for production of H2 using [p-MeOC6H4NH3][BF4] (pKa MeCN = 11.86), with a turnover frequency of 350 s-1 and an overpotential of 0.86 V at Ecat/2. A pKa value of 15.6 was measured in CH3CN for [CpC5F4NCoIII(PtBu 2NPh 2)H], which was used in conjunction with electrochemical measurements to obtain thermodynamic data for cleavage of the Co-H bond.",
author = "Ming Fang and Eric Wiedner and Dougherty, {William G.} and Kassel, {W. Scott} and Tianbiao Liu and DuBois, {Daniel L} and Bullock, {R Morris}",
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T1 - Cobalt complexes containing pendant amines in the second coordination sphere as electrocatalysts for H2 production

AU - Fang, Ming

AU - Wiedner, Eric

AU - Dougherty, William G.

AU - Kassel, W. Scott

AU - Liu, Tianbiao

AU - DuBois, Daniel L

AU - Bullock, R Morris

PY - 2014/10/27

Y1 - 2014/10/27

N2 - A series of heteroleptic 17e cobalt complexes, [CpCoII(PtBu 2NPh 2)](BF4), [CpC6F5CoII(PtBu 2NPh 2)](BF4), and [CpC5F4NCoII(PtBu 2NPh 2)](BF4) (where PtBu 2NPh 2 = 1,5-diphenyl-3,7-di-tert-butyl-1,5-diaza-3,7-diphosphacyclooctane, CpC6F5 = C5H4(C6F5), and CpC5F4N = C5H4(C5F4N)) were synthesized, and the structures of all three were determined by X-ray crystallography. Electrochemical studies showed that the CoIII/II couple of [CpC5F4NCoII(PtBu 2NPh 2)]+ appears 250 mV positive of the CoIII/II couple of [CpCoII(PtBu 2NPh 2)]+ as a result of the strongly electron withdrawing perfluoropyridyl substituent on the Cp ring. Reduction of these paramagnetic CoII complexes by KC8 led to the diamagnetic 18e complexes CpCoI(PtBu 2NPh 2), CpC6F5CoI(PtBu 2NPh 2), and CpC5F4NCoI(PtBu 2NPh 2), which were also characterized by crystallography. Protonation of these neutral CoI complexes led to the CoIII hydrides [CpCoIII(PtBu 2NPh 2)H](BF4), [CpC6F5CoIII(PtBu 2NPh 2)H](BF4), and [CpC5F4NCoIII(PtBu 2NPh 2)H](BF4), and crystal structures of each of these cobalt hydrides were determined. The cobalt complex with the most electron withdrawing Cp ligand, [CpC5F4NCoII(PtBu 2NPh 2)]+, is an electrocatalyst for production of H2 using [p-MeOC6H4NH3][BF4] (pKa MeCN = 11.86), with a turnover frequency of 350 s-1 and an overpotential of 0.86 V at Ecat/2. A pKa value of 15.6 was measured in CH3CN for [CpC5F4NCoIII(PtBu 2NPh 2)H], which was used in conjunction with electrochemical measurements to obtain thermodynamic data for cleavage of the Co-H bond.

AB - A series of heteroleptic 17e cobalt complexes, [CpCoII(PtBu 2NPh 2)](BF4), [CpC6F5CoII(PtBu 2NPh 2)](BF4), and [CpC5F4NCoII(PtBu 2NPh 2)](BF4) (where PtBu 2NPh 2 = 1,5-diphenyl-3,7-di-tert-butyl-1,5-diaza-3,7-diphosphacyclooctane, CpC6F5 = C5H4(C6F5), and CpC5F4N = C5H4(C5F4N)) were synthesized, and the structures of all three were determined by X-ray crystallography. Electrochemical studies showed that the CoIII/II couple of [CpC5F4NCoII(PtBu 2NPh 2)]+ appears 250 mV positive of the CoIII/II couple of [CpCoII(PtBu 2NPh 2)]+ as a result of the strongly electron withdrawing perfluoropyridyl substituent on the Cp ring. Reduction of these paramagnetic CoII complexes by KC8 led to the diamagnetic 18e complexes CpCoI(PtBu 2NPh 2), CpC6F5CoI(PtBu 2NPh 2), and CpC5F4NCoI(PtBu 2NPh 2), which were also characterized by crystallography. Protonation of these neutral CoI complexes led to the CoIII hydrides [CpCoIII(PtBu 2NPh 2)H](BF4), [CpC6F5CoIII(PtBu 2NPh 2)H](BF4), and [CpC5F4NCoIII(PtBu 2NPh 2)H](BF4), and crystal structures of each of these cobalt hydrides were determined. The cobalt complex with the most electron withdrawing Cp ligand, [CpC5F4NCoII(PtBu 2NPh 2)]+, is an electrocatalyst for production of H2 using [p-MeOC6H4NH3][BF4] (pKa MeCN = 11.86), with a turnover frequency of 350 s-1 and an overpotential of 0.86 V at Ecat/2. A pKa value of 15.6 was measured in CH3CN for [CpC5F4NCoIII(PtBu 2NPh 2)H], which was used in conjunction with electrochemical measurements to obtain thermodynamic data for cleavage of the Co-H bond.

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