Photocatalytic CO2 reduction using a Mn complex as a catalyst

Abstract

Summary

A photochemical reduction of CO₂ to formic acid was shown using the manganese complex Mn(bpy)(CO)3Br as catalyst in combination with the ruthenium-based photosensitizer [Ru(dmb)3][PF6]2 or Ru(bpy)3. Turnover numbers (TONs) of up to 157 and selectivities up to 85% for formate were reached in DMF. The experiments were conducted under visible-light irradiation (λ = 480 nm) using TEOA and BNAH as sacrificial electron donors (see section SEDs below).

Advances and special progress

A manganese complex previously reported for electrocatalytic CO₂ reduction was shown to photocatalytically reduce CO₂ to formic acid.

Additional remarks

In acetonitrile, a considerable amount of CO was formed in addition to the reduction of CO₂ to formic acid whereas the CO₂ reduction attempts in DMF yielded almost no CO.

Content of the published article in detail

The article contains results for the reduction of CO₂ to formate under visible-light catalysis using a manganese complex and a ruthenium-based photosensitizer. The catalytic system performs best (referring to the TON of formate production) in DMF.

Catalyst

Mn(bpy)(CO)3Br

Photosensitizer

[Ru(dmb)3][PF6]2 Ru(bpy)3

Investigation

	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.	Mn(bpy)(CO)3Br	0.05	[Ru(dmb)3][PF6]2	0.05	BNAH	0.1	DMF				480		2		4
2.	Mn(bpy)(CO)3Br	0.05	[Ru(dmb)3][PF6]2	0.05	BNAH	0.1	DMF				480		8	1	67
3.	Mn(bpy)(CO)3Br	0.05	[Ru(dmb)3][PF6]2	0.05	BNAH	0.1	DMF				480		12	14	149
4.	Mn(bpy)(CO)3Br	0.05	[Ru(dmb)3][PF6]2	0.05	BNAH	0.1	DMF			Argon gas	480		2	49	4
5.			[Ru(dmb)3][PF6]2	0.05	BNAH	0.1	DMF				480		1	4	8
6.			[Ru(dmb)3][PF6]2	0.05	BNAH	0.1	DMF				480		3	11	25
7.	Mn(bpy)(CO)3Br	0.05			BNAH	0.1	DMF				480		3		1
8.	Mn(bpy)(CO)3Br	0.05	[Ru(dmb)3][PF6]2	0.05	BNAH	0.1	DMA				480		9	14	98
9.			[Ru(dmb)3][PF6]2	0.05	BNAH	0.1	DMA				480		3	7	19
10.	Mn(bpy)(CO)3Br	0.05	[Ru(dmb)3][PF6]2	0.05	BNAH	0.1	MeCN				480		40	17	78
11.			[Ru(dmb)3][PF6]2	0.05	BNAH	0.1	MeCN				480		2	12	14
12.	Mn(bpy)(CO)3Br	0.05	Ru(bpy)3	0.05	BNAH	0.1	DMF				480		12	8	157

Experiment-Name: Photocatalytic CO2 reduction: conditions optimizationExport

Sacrificial Electron Donor

In this study, the experiments were done with the sacrificial electron donor TEOA (100507) and BNAH (1-benzyl-14-dihydronicotinamide).

Additives

In this study, a control experiment under argon atmosphere was conducted.