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

Investigation-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

Investigation-Name: Time profile in DMFExport

1. REDIRECT Study on the concentration of catalyst

Investigation-Name: Table 1Export

	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

Investigation-Name: Effect of proton donorExport

Sacrificial electron donor

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

Additives

No additives were tested in this study.