Highly Efficient and Robust Photocatalytic Systems for CO2 Reduction Consisting of a Cu(I) Photosensitizer and Mn(I) Catalysts

Abstract

Summary

A photochemical reduction of CO₂ to CO or formic acid was shown using the manganese complexes Mn(bpy)(CO)3Br (100752), (100845) or Mn(oMesbpy)(CO)2Br (100705) as catalyst in combination with the copper-based photosensitizer [Cu(phen)-(dPPh-Bu)2]2[PF6]2 (100828). Turnover numbers (TONs) over 1300 for CO were reached in dimethylacetamide/TEOA for complex (100845). The highest selectivity for CO (96%) was obtained for catalyst Mn(oMesbpy)(CO)2Br (100705) while catalyst Mn(bpy)(CO)3Br (100752) allowed for the reduction of CO₂ to formic acid with a selectivity of 74%. The experiments were conducted under visible-light irradiation (λ = 436 nm) using BIH as sacrificial electron donor (see section SEDs below).

Advances and special progress

Employing catalyst (100845), the highest quantum yield for CO₂ reduction using abundant elements (57%) at that time was achieved. The authors also demonstrated the stability of their catalyst over a 36 h experiment, where it was shown that BIH was the limiting factor, even in large amounts.

Additional remarks

The authors could show that the substituents on the manganese complexes largely influenced the photocatalytic efficiency and product selectivity.

Content of the published article in detail

The article contains results for the reduction of CO₂ to CO and formic acid under visible-light catalysis using manganese complexes as catalysts. The catalytic system performs best (referring to the TON of CO production) in DMA/TEOA.

Catalyst

(100751) [Show R-Groups] Mn(oMesbpy)(CO)2Br (100705)

Photosensitizer

[Cu(phen)-(dPPh-Bu)2]2[PF6]2 (100828)

Investigation

		cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	.	.	λexc [nm]	.	TON CO	.	TON H2	TON HCOOH	.	.	.	.
(edit)	1.	Mn(bpy)(CO)3Br	0.05	[Cu(phen)-(dPPh-Bu)2]2[PF6]2	0.25	BIH	0.01	MeCN			436		50		4	157
(edit)	2.	Molecule:100845	0.05	[Cu(phen)-(dPPh-Bu)2]2[PF6]2	0.25	BIH	0.01	MeCN			436		164		1	65
(edit)	3.	Mn(oMesbpy)(CO)2Br	0.05	[Cu(phen)-(dPPh-Bu)2]2[PF6]2	0.25	BIH	0.01	MeCN			436		208		0.5	5

Investigation-Name: Results for photocatalytic reduction of CO2

		cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	.	.	λexc [nm]	.	TON CO	TON H2	TON HCOOH	.	.
(edit)	1.	Molecule:100845	0.05	[Cu(phen)-(dPPh-Bu)2]2[PF6]2	0.25	BIH	0.1	MeCN			436 nm		1004	68	310

Investigation-Name: Durability test

Sacrificial electron donor

In this study, the experiments were done with the sacrificial electron donors TEOA (100507) and BIH (100508).

Additives

In this study, no additives were tested.