Effective Pincer Cobalt Precatalysts for Lewis Acid Assisted CO2 Hydrogenation

Effective Pincer Cobalt Precatalysts for Lewis Acid Assisted CO2 Hydrogenation

Ariana Z. Spentzos, Charles L. Barnes, and Wesley H. Bernskoetter*

University of Missouri

http://pubs.acs.org/doi/pdf/10.1021/acs.inorgchem.6b01454

Inorg. Chem. 

DOI: 10.1021/acs.inorgchem.6b01454

TOC:


Abstract:

The pincer ligand MeN[CH2CH2(PiPr2)]2 (iPrPNP) was employed to support a series of cobalt(I) complexes, which were crystallographically characterized. A cobalt monochloride species, (iPrPNP)CoCl, served as a precursor for the preparation of several cobalt precatalysts for CO2 hydrogenation, including a cationic dicarbonyl cobalt complex, [(iPrPNP)Co(CO)2]+. When paired with the Lewis acid lithium triflate, [(iPrPNP)Co(CO)2]+ affords turnover numbers near 30 000 (at 1000 psi, 45 °C) for CO2-to-formate hydrogenation, which is a notable increase in activity from previously reported homogeneous cobalt catalysts. Though mechanistic information regarding the function of the precatalysts remains limited, multiple experiments suggest the active species is a molecular, homogeneous [(iPrPNP)Co] complex.

Polymer Coordination Promotes Selective CO2 Reduction by Cobalt Phthalocyanine

Polymer Coordination Promotes Selective CO2 Reduction by Cobalt Phthalocyanine

Wesley W Kramer and Charles McCrory

Chem. Sci., 2016, Accepted Manuscript
DOI: 10.1039/C5SC04015A
Received 22 Oct 2015, Accepted 01 Feb 2016

Cobalt phthalocyanine (CoPc) is a known electrocatalyst for the carbon dioxide reduction reaction (CO2RR) that, when adsorbed onto edge-plane graphite (EPG) electrodes, shows modest activity and selectivity for CO production along with co-generation of H2. In contrast, electrodes modified with CoPc immobilized in a poly-4-vinylpridine (P4VP) film show dramatically enhanced activity and selectivity compared to those modified CoPc alone. CoPc-P4VP films display a Faradaic efficiency of ~90% for CO production, with a turnover frequency of 4.8 s-1 at just -0.75 V vs RHE. Two properties of P4VP contribute to enhancing the activity of CoPc; (1) the ability of individual pyridine residues to coordinate to CoPc and (2) the high concentration of uncoordinated pyridine residues throughout the film which may enhance the catalytic activity of CoPc through secondary and other outer coordination sphere effects. Electrodes modified with polymer-free, five-coordinate CoPc(py) films (py = pyridine) and with CoPc catalysts immobilized in non-coordinating poly-2-vinylpyridine films were prepared to independently investigate the role that each property plays in enhancing CO2RR performance of CoPc-P4VP. These studies show that a synergistic relationship between the primary and outer coordination sphere effects is responsible for the enhanced catalytic activity of CoPc when embedded in the P4VP membrane.

Homogeneous Cobalt Catalyst for Hydrogenation of Carboxylic Acids

http://www.sciencemag.org/content/350/6258/298.abstract

 

Science 16 October 2015:
Vol. 350 no. 6258 pp. 298-302
DOI: 10.1126/science.aaa8938

Hydrogenation of carboxylic acids with a homogeneous cobalt catalyst

1. Ties J. Korstanje,
2. Jarl Ivar van der Vlugt,
3. Cornelis J. Elsevier*,
4. Bas de Bruin*

The reduction of esters and carboxylic acids to alcohols is a highly relevant conversion for the pharmaceutical and fine-chemical industries and for biomass conversion. It is commonly performed using stoichiometric reagents, and the catalytic hydrogenation of the acids previously required precious metals. Here we report the homogeneously catalyzed hydrogenation of carboxylic acids to alcohols using earth-abundant cobalt. This system, which pairs Co(BF₄)₂·6H₂O with a tridentate phosphine ligand, can reduce a wide range of esters and carboxylic acids under relatively mild conditions (100°C, 80 bar H₂) and reaches turnover numbers of up to 8000.