Highly Efficient and Selective Photocatalytic CO2 Reduction by Iron and Cobalt Quaterpyridine Complexes

Abstract

Summary

A photochemical reduction of CO₂ to CO was shown using the cobalt complex [Fe(qpy)(H2O)2][ClO4]2 or the iron complex [Co(qpy)(H2O)2][ClO4]2 as catalysts in combination with the ruthenium-based photosensitizer Ru(bpy)3Cl2. Turnover numbers (TONs) up to 2660 and a selectivity of 98% for CO using the cobalt catalyst and TONs of >3000 and a selectivity of 95% for CO using the iron catalyst were reached in acetonitrile/triethanolamine. When swapping the ruthenium photosensitizer for the organic dye sensitizer purpurin, TONs of 790 and 1365 in DMF were obtained for the cobalt and iron catalysts, respectively. The experiments were conducted under visible-light irradiation (λ = 460 nm) using BIH as sacrificial reductant (see section SEDs below).

Advances and special progress

The photocatalytic reduction of CO₂ to CO by cobalt and iron complexes was shown with some of the highest TONs for homogeneous photocatalytic CO2 reduction at that time and the (back then) highest TON for a system of fully earth-abundant materials was achieved.

Content of the published article in detail

The article contains results for the reduction of CO₂ to CO under visible-light catalysis using cobalt and iron quaterpyridine complexes as catalysts. The catalytic system performs best (referring to the TON of CO production) in acetonitrile/triethanolamine using the cobalt complex and the ruthenium photosensitizer.

Catalysts

[Fe(qpy)(H2O)2][ClO4]2 [Co(qpy)(H2O)2][ClO4]2 Co(ClO4)2

Photosensitizers

Ru(bpy)3Cl2 purpurin

Investigations

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	.	.	solvent A	additives	λexc [nm]	.	TON CO	TON H2	TON HCOOH	.
1.	[Co(qpy)(H2O)2][ClO4]2	0.005	Ru(bpy)3Cl2	0.3	BIH	0.1			MeCN		460 (LED)		2660	23	35
2.	[Co(qpy)(H2O)2][ClO4]2	0	Ru(bpy)3Cl2	0.3	BIH	0.1			MeCN		460 (LED)		0	2	1
3.	[Co(qpy)(H2O)2][ClO4]2	0.005	Ru(bpy)3Cl2	0.3	BIH	0.1			MeCN	Argon atmosphere	460 (LED)		0	33	0
4.	[Co(qpy)(H2O)2][ClO4]2	0.005	Ru(bpy)3Cl2	0.3	BIH	0.1			MeCN		460 (LED)		182	0	11
5.	[Co(qpy)(H2O)2][ClO4]2	0.005	Ru(bpy)3Cl2	0.3					MeCN		460 (LED)		114	25	25
6.	[Co(qpy)(H2O)2][ClO4]2	0.01	Ru(bpy)3Cl2	0.3	BIH	0.1			MeCN		460 (LED)		1875	11	18
7.	[Co(qpy)(H2O)2][ClO4]2	0.2	Ru(bpy)3Cl2	0.3	BIH	0.1			MeCN		460 (LED)		1262	7	23
8.	[Co(qpy)(H2O)2][ClO4]2	0.05	Ru(bpy)3Cl2	0.3	BIH	0.1			MeCN		460 (LED)		497	5	3
9.	[Co(qpy)(H2O)2][ClO4]2	0.05	Ru(bpy)3Cl2	0.3					MeCN		460 (LED)		0	1	1
10.	[Co(qpy)(H2O)2][ClO4]2	0.1	Ru(bpy)3Cl2	0.3	BIH	0.1			MeCN		460 (LED)		466	2	22
11.	[Co(qpy)(H2O)2][ClO4]2	0.05	Ru(bpy)3Cl2	0.5	BIH	0.1			MeCN		460 (LED)		521	49	6
12.	[Co(qpy)(H2O)2][ClO4]2	0	Ru(bpy)3Cl2	0.5	BIH	0.1			MeCN		460 (LED)		136	43	5
13.	[Co(qpy)(H2O)2][ClO4]2	0.05	Ru(bpy)3Cl2	0.2	BIH	0.1			MeCN		460 (LED)		366	15	4
14.	[Co(qpy)(H2O)2][ClO4]2	0.05	Ru(bpy)3Cl2	0.2	BIH	0.1			MeCN	Argon atmosphere	460 (LED)		0	3	1
15.	[Co(qpy)(H2O)2][ClO4]2	0	Ru(bpy)3Cl2	0.2	BIH	0.1			MeCN		460 (LED)		0	6	1
16.	Co(ClO4)2	0.05	Ru(bpy)3Cl2	0.3	BIH	0.1			MeCN		460 (LED)		33	11	1
17.	[Co(qpy)(H2O)2][ClO4]2	0.05	Ru(bpy)3Cl2	0.3					MeCN		460 (LED)		0	1	1

Investigation-Name: Optimizations of conditions for Co(qpy)(H2O)2(ClO4)2 and Ru(bpy)3Cl2Export

1. REDIRECT Optimizations of conditions for Fe(qpy)(H2O)2(ClO4)2 and Ru(bpy)3Cl2

Investigation-Name: Fe(qpy)(H2O)2(ClO4)2 and Ru(bpy)3Cl2Export

1. REDIRECT Optimizations of conditions for Co(qpy)(H2O)2(ClO4)2 and purpurin

Investigation-Name: Co(qpy)(H2O)2(ClO4)2 and purpurinExport

1. REDIRECT Optimizations of conditions for Fe(qpy)(H2O)2(ClO4)2

Investigation-Name: Fe(qpy)(H2O)2(ClO4)2Export

Sacrificial electron donor

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

Additives

In this study, control experiments were conducted under an argon atmosphere.