Visible-Light Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic Carbene–Isoquinoline Complex

Abstract

Summary

The synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene-amine ligands for the highly-selective conversion of CO₂ to CO has been shown. Turnover number (TON) of 98,000 and turnover frequency of 3.9 s^-1 were achieved using the nickel catalyst [Ni(bimiqpr)][PF6]2 in combination with the iridium complex Ir(ppy)3 as the photosensitizer under visible-light catalysis. The experiments were performed using a Xenon lamp as the visible-light source with triethylamine as sacrificial electron donor.

Advances and special progress

The reported novel earth-abundant complexes also emerged as catalysts for the electrochemical CO₂ conversion to CO. Among them, the complex [Ni(bimiqpr)][PF6]2 had the lowest cathodic onset potential of Ecat = −1.2 V vs SCE.

Additional remarks

Further studies have revealed that the overall efficiency of the developed solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO₂ to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion

Content of the published article in detail

The article contains results for the synthesis and characterization of novel earth-abundant nickel complexes, as well as for the photochemical reduction of CO₂ to CO. The catalytic system performed best (referring to the TON of CO production) using the complex [Ni(bimiqpr)][PF6]2 as the catalyst.

Catalyst

[Ni(bimiqpr)][PF6]2

Photosensitizer

Ir(ppy)3

Investigation

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	λexc [nm]	.	TON CO	.	.	.	.
1.	[Ni(bimiqpr)][PF6]2	0.000002	Ir(ppy)3	0.2	TEA	0.07	MeCN	solar spectrum		98000
2.	[Ni(bimiqpr)][PF6]2	0.00002	Ir(ppy)3	0.2	TEA	0.07	MeCN	solar spectrum		9000
3.	[Ni(bimiqpr)][PF6]2	0.0002	Ir(ppy)3	0.2	TEA	0.07	MeCN	solar spectrum		1500

Investigation-Name: Table 1Export

Sacrificial electron donor

In this study, the experiments were done with the sacrificial electron donor triethylamine (TEA).

Additives

In this study, no additives were used.