Hydrogenation of CO2 in Water Using a Bis(diphosphine) Ni–H Complex

• Published in: ACS catalysis 2017-04, Vol.7 (4), p.3089-3096
• Main Authors: Burgess, Samantha A, Kendall, Alexander J, Tyler, David R, Linehan, John C, Appel, Aaron M
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.7b00350

The water-soluble Ni bis­(diphosphine) complex [NiL 2]­(BF4)2 (L = 1,2-[bis­(dimethoxypropyl)­phosphino]­ethane and the corresponding hydride, [HNiL 2]­BF4, were synthesized and characterized. These complexes were specifically designed for CO2 hydrogenation. For HNiL 2 +, the hydricity (ΔG°H– ) was determined to be 23.2(3) kcal/mol in aqueous solution. On the basis of the hydricity of formate, 24.1 kcal/mol, the transfer of a hydride from HNiL 2 + to CO2 to produce formate is favorable by 1 kcal/mol. Starting from either NiL 2 2+ or HNiL 2 + in water, catalytic hydrogenation of CO2 was observed with NaHCO3 (0.8 M) as the only additive. A maximum turnover frequency of [4.0(5)] × 10–1 h–1 was observed at 80 °C and 34 atm of a 1:1 mixture of CO2 and H2. This report demonstrates the use of a homogeneous first-row transition-metal catalyst for CO2 hydrogenation in water using NaHCO3 as an inexpensive, readily available base.