Nickel(II) pincer complexes demonstrate that the remote substituent controls catalytic carbon dioxide reduction

Abstract

Summary

A photochemical reduction of CO₂ to CO was shown using the nickel complex Ni(4O(-)py)-(MeNHC)2Cl in comparison to the inactive derivative [Ni(py)-(MeNHC)2(MeCN)][PF6]2 as catalyst in combination with the iridium-based photosensitizer Ir(ppy)3. Turnover numbers (TONs) of 10.6 for CO with the cobalt complex Ni(4O(-)py)-(MeNHC)2Cl were reached in acetonitrile. The experiments were conducted under visible-light irradiation using BIH and TEA as sacrificial electron donors (see section SEDs below).

Advances and special progress

The authors showed the importance of remote substituents by a drastic change in activity through a change in a remote substituent.

Additional remarks

The designed photocatalyst could be turned on and off via (de)protonation.

Content of the published article in detail

The article contains results for the reduction of CO₂ to CO under visible-light catalysis using nickel complexes as catalysts. The catalytic system performs best (referring to the TON of CO production) in acetonitrile with the cobalt catalyst Ni(4O(-)py)-(MeNHC)2Cl.

Catalyst

Ni(4O(-)py)-(MeNHC)2Cl [Ni(py)-(MeNHC)2(MeCN)][PF6]2

Photosensitizer

Ir(ppy)3

Investigation

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	additives	λexc [nm]	TON CO	.
1.	Ni(4O(-)py)-(MeNHC)2Cl	0.1	Ir(ppy)3	0.1	BIH	0.011	MeCN	TEA	solar spectrum	10.6
2.	[Ni(py)-(MeNHC)2(MeCN)][PF6]2	0.1	Ir(ppy)3	0.1	BIH	0.011	MeCN	TEA	solar spectrum	0.1
3.	Ni(4O(-)py)-(MeNHC)2Cl	0.1	Ir(ppy)3	0.1	BIH	0.011	DMF	TEA	solar spectrum	9
4.	[Ni(py)-(MeNHC)2(MeCN)][PF6]2	0.1	Ir(ppy)3	0.1	BIH	0.011	DMF	TEA	solar spectrum	0.5
5.	Ni(4O(-)py)-(MeNHC)2Cl	0.1	Ir(ppy)3	0.1	BIH	0.011	MeCN		solar spectrum	1.8
6.	Ni(4O(-)py)-(MeNHC)2Cl	0.1	Ir(ppy)3	0.1	BIH	0.011	MeCN	proton sponge	solar spectrum	5.6
7.	Ni(4O(-)py)-(MeNHC)2Cl	0.1	Ir(ppy)3	0.1	BIH	0.011	MeCN	TfOH	solar spectrum	0.9
8.	Ni(4O(-)py)-(MeNHC)2Cl	0.1			BIH	0.011	MeCN	TEA	solar spectrum	0.6
9.	Ni(4O(-)py)-(MeNHC)2Cl	0.1	Ir(ppy)3	0.1			MeCN	TEA	solar spectrum	0.3
10.	Ni(4O(-)py)-(MeNHC)2Cl	0.1	Ir(ppy)3	0.1	BIH	0.011	MeCN	N2	solar spectrum	0.2

Investigation-Name: Photocatalytic CO2 reduction under varied conditionsExport

Sacrificial Electron Donor

In this study, the experiments were done with the sacrificial electron donors BIH (BIH) and TEA (TEA).

Additives

In this study, TfOH and proton sponge were used as additives to (de)protonate the catalytically active nickel complex. Moreover, a control experiment under nitrogen atmosphere was conducted.