An integrated Re(I) photocatalyst and sensitizer that activates the formation of formic acid from reduction of CO2

Abstract

Summary

A photochemical reduction of CO₂ to formic acid was shown using the rhenium catalyst and sensitizer [Re(bpy)2(CO)2][OTf] in combination with the supplemental photosensitizer [Ru(bpy)3][PF6]. Turnover numbers (TONs) up to 2750 for formic acid were reached in dimethylacetamide. The experiments were conducted under visible-light irradiation (λ = 405 nm) with TEOA (see section SEDs below) as sacrificial electron donor.

Advances and special progress

A unprecedented rhenium complex was used as an integrated photosensitizer/catalyst to generate formic acid from CO₂; other rhenium catalysts only allow for the formation of CO as the reduction product.

Additional remarks

The complex [Re(bpy)2(CO)2][OTf] can act both as a photocatalyst and sensitizer, but its performance is considerably enhanced by the addition of [Ru(bpy)3][PF6] as supplemental photosensitizer. The variation of the catalyst concentration also showed a drastic influence on the performance of the catalytic system.

Content of the published article in detail

The article contains results for the reduction of CO₂ to formic acid under visible-light catalysis using a rhenium complex as a catalyst. The catalytic system performs best (referring to the TON of formic acid production) in dimethylacetamide.

Catalyst

[Re(bpy)2(CO)2][OTf]

Photosensitizer

[Ru(bpy)3][PF6]

Investigations

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	solvent A	.	.	λexc [nm]	.	TON H2	TON HCOOH	.
1.			[Ru(bpy)3][PF6]	0.8	TEOA	DMA			405 nm		1.75	12.5
2.			[Ru(bpy)3][PF6]	0.8	TEOA	DMF			405 nm		2	15
3.			[Ru(bpy)3][PF6]	0.8	TEOA	MeCN			405 nm		1.5	2.5
4.	[Re(bpy)2(CO)2][OTf]	0.8			TEOA	DMA			405 nm			10.3
5.	[Re(bpy)2(CO)2][OTf]	0.8	[Ru(bpy)3][PF6]	0.8	TEOA	DMA			405 nm		1.5	52
6.	[Re(bpy)2(CO)2][OTf]	0.8			TEOA	DMF			405 nm		0.8	10.8
7.	[Re(bpy)2(CO)2][OTf]	0.8	[Ru(bpy)3][PF6]	0.8	TEOA	DMF			405 nm		2.8	66
8.	[Re(bpy)2(CO)2][OTf]	0.8	[Ru(bpy)3][PF6]	0.8	TEOA	MeCN			405 nm
9.	[Re(bpy)2(CO)2][OTf]	0.8	[Ru(bpy)3][PF6]	0.8	TEOA	MeCN			405 nm		2.8	11.5

Experiment-Name: Solvent effect study between DMA DMF and acetonitrileExport

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	solvent A	.	.	λexc [nm]	.	TON H2	TON HCOOH	.
1.	[Re(bpy)2(CO)2][OTf]	0.2	[Ru(bpy)3][PF6]	0.2	TEOA	DMF			405 nm		0	0
2.	[Re(bpy)2(CO)2][OTf]	0.2	[Ru(bpy)3][PF6]	0.2	TEOA	DMF			405 nm		1	12.5
3.	[Re(bpy)2(CO)2][OTf]	0.2	[Ru(bpy)3][PF6]	0.2	TEOA	DMF			405 nm		2.5	19.5
4.	[Re(bpy)2(CO)2][OTf]	0.2	[Ru(bpy)3][PF6]	0.2	TEOA	DMF			405 nm		4.5	50.5
5.	[Re(bpy)2(CO)2][OTf]	0.2	[Ru(bpy)3][PF6]	0.2	TEOA	DMF			405 nm		6	59.5
6.	[Re(bpy)2(CO)2][OTf]	0.2	[Ru(bpy)3][PF6]	0.2	TEOA	DMF			405 nm		8.5	69.25

Experiment-Name: Time profile in DMFExport

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	solvent A	.	.	λexc [nm]	.	TON H2	TON HCOOH	.	.	.	.
1.	[Re(bpy)2(CO)2][OTf]	1			TEOA	DMA			405			10.3
2.	[Re(bpy)2(CO)2][OTf]	1	[Ru(bpy)3][PF6]	1	TEOA	DMA			405		1.5	52
3.	[Re(bpy)2(CO)2][OTf]	0.5	[Ru(bpy)3][PF6]	1	TEOA	DMA			405		15	115
4.	[Re(bpy)2(CO)2][OTf]	0.2	[Ru(bpy)3][PF6]	1	TEOA	DMA			405		24	275
5.	[Re(bpy)2(CO)2][OTf]	0.1	[Ru(bpy)3][PF6]	1	TEOA	DMA			405		38	428
6.	[Re(bpy)2(CO)2][OTf]	0.05	[Ru(bpy)3][PF6]	1	TEOA	DMA			405		50	535
7.	[Re(bpy)2(CO)2][OTf]	0.02	[Ru(bpy)3][PF6]	1	TEOA	DMA			405		225	1480
8.	[Re(bpy)2(CO)2][OTf]	0.01	[Ru(bpy)3][PF6]	1	TEOA	DMA			405		375	2750

Experiment-Name: Study on the concentration of catalystExport

	cat	PS	e-D	solvent A	.	.	additives	λexc [nm]	.	TON H2	TON HCOOH	.
1.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEOA	DMF			water	405 nm		4.25	25
2.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEOA	DMF			water	405 nm		5.75	25.75
3.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEOA	DMF			phenol	405 nm		5.25	27
4.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEOA	DMF			phenol	405 nm		5.75	19
5.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEA	DMF			water	405 nm		2	12.5
6.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEA	DMF			water	405 nm		2.75	14.5
7.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEA	DMF			phenol	405 nm		1	10.25
8.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEA	DMF			phenol	405 nm		16.25	11.25
9.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEOA	DMA			water	405 nm		3.25	20.5
10.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEOA	DMA			water	405 nm		3.5	24
11.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEOA	DMA			phenol	405 nm		7.75	30
12.	[Re(bpy)2(CO)2][OTf]	[Ru(bpy)3][PF6]	TEOA	DMA			phenol	405 nm		9	34.75

Experiment-Name: Effect of proton donorExport

Sacrificial electron donor

In this study, the experiments were done with the sacrificial electron donor TEOA (100507).

Additives

In this study, the experiments were done with the additives water (H2O) and phenol (PhOH).