Exchange Coupling Determines Metal-Dependent Efficiency for Iron- and Cobalt-Catalyzed Photochemical CO2 Reduction

Abstract

Summary

A photochemical reduction of CO2 to CO was shown using an Fe2+ and Co2+ complex as catalysts in combination with different photosensitizers. The authors examined the efficiency for photocatalytic CO2RR pending on metal−ligand exchange coupling as an example of charge delocalization. The iron complex 100968 and cobalt complexes100969, both bearing the redox-active ligand tpyPY2Me were tested in comparison. It was found that the two-electron reduction of the Co(tpyPY2Me)]2+ catalyst 100969 occurs at potentials 770 mV more negative than the Fe(tpyPY2Me)]2+ analogue100968 due to maximizing the exchange coupling in the latter compound.

Catalysts tested in this study

100968 100969

Photosensitizer

Ru(bpy)3 3,6-Diamino-10-methylacridinium 100971 Ir(ppy)3

Investigation

General details for the experimental setup: Conducted inside a 25 mL borosilicate culture tube with a stir bar, a rubber septum, and an aluminum crimped top. The reaction vessel contained 5 mL of CH3CN, 2 μM of the catalyst, 200 μM of the photosensitizer, 100 mM BIH (112 mg), and 1 M phenol (470 mg). The reaction tubes were sparged with CO2 for 10 min, followed by injection of a gaseous internal standard (0.1 mL of C2H6). The reactions were placed on a stirplate 13 cm from two Kessil blue LED lamps (440 nm) for 15 or 30 min at a time and maintained at ambient temperature using a fan. Analysis of the headspace by Gas Chromatography (GC).

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	.	.	solvent A	additives	.	.	TON CO	TON H2	.	.
1.	Molecule:100968	2	Ru(bpy)3	0.2	BIH	0.1			MeCN				15520	86
2.	Molecule:100968	0.2	Ru(bpy)3	0.2	BIH	0.1			MeCN				30349	1013
3.			Ru(bpy)3	0.2	BIH	0.1			MeCN				43	52
4.	Molecule:100968	2			BIH	0.1			MeCN				112	0
5.	Molecule:100968	2	Ru(bpy)3	0.2					MeCN				150	0
6.	Molecule:100968	2	Ru(bpy)3	0.2	BIH	0.1			MeCN				6	0
7.	Molecule:100968	2	Ru(bpy)3	0.2	BIH	0.1			MeCN	Ar			0	222
8.	Molecule:100968	2	Molecule:100971	0.2	BIH	0.1			MeCN				12749	163
9.	Molecule:100968	0.2	Molecule:100971	0.2	BIH	0.1			MeCN				28712	6527
10.	Molecule:100968	2	Ir(ppy)3	0.2	BIH	0.1			MeCN				18502	141
11.	Molecule:100968	2	Molecule:100970	0.2	BIH	0.1			MeCN				6710	0

Investigation-Name: CO2 Reduction under diverse conditions with diverse sensitizersExport

The values in Table 2 include TOF numbers given in TON/min

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	.	.	solvent A	.	.	.	.	.	.
1.	Molecule:100969	2	Ru(bpy)3	0.2	BIH	0.1			MeCN
2.	Molecule:100969	2	Molecule:100971	0.2	BIH	0.1			MeCN
3.	Molecule:100969	2	Ir(ppy)3	0.2	BIH	0.05			MeCN
4.	Molecule:100969	2	Molecule:100971	0.2	BIH	0.05			MeCN
5.	Molecule:100969	2	Ru(bpy)3	0.2	BIH	0.05			MeCN
6.	Molecule:100969	2	Molecule:100971	0.2	TEA	0.05			MeCN
7.	Molecule:100969	2	Molecule:100971	0.2	TEA	0.05			MeCN
8.	Molecule:100969	2	Molecule:100971	0.2	TEA	0.05			MeCN
9.	Molecule:100969	2	Molecule:100971	0.2	TEA	0.05			MeCN

Investigation-Name: Results Co2+ experiments taken from SIExport

Further Information

The results for the catalytic activity of the Co2+ compound 100969 in Table 2 were gained from the Supporting Information.

Sacrificial electron donor

In this study, the experiments were done with the sacrificial electron donor BIH (100508).

Additives

Different sources of protons were used, e.g. PhOH, TFE and 4-CHLOROPHENOL

Tags

TagContains tags that describe the content of the page.: photocatalytic CO2 reduction (Ontology: voc4cat, OBOID: voc4cat:0000099), TagContains tags that describe the content of the page.: CO