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 language | English |
|---|---|
| Pages (from-to) | 5820-5833 |
| Number of pages | 14 |
| Journal | Organometallics |
| Volume | 33 |
| Issue number | 20 |
| DOIs | |
| Publication status | Published - Oct 27 2014 |
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ASJC Scopus subject areas
- Organic Chemistry
- Physical and Theoretical Chemistry
- Inorganic Chemistry
Cite this
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 journal › Article
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TY - JOUR
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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U2 - 10.1021/om5004607
DO - 10.1021/om5004607
M3 - Article
VL - 33
SP - 5820
EP - 5833
JO - Organometallics
JF - Organometallics
SN - 0276-7333
IS - 20
ER -