Mn-carbonyl molecular catalysts containing a redox-active phenanthroline-5,6-dione for selective electro- and photoreduction of CO2 to CO or HCOOH

Abstract

Summary

A photochemical reduction of CO₂ to CO or formic acid was shown using the manganese complexes Mn(phdk)(CO)3Br or Mn(phdk)(CO)3(MeCN) as catalyst in combination with the ruthenium-based photosensitizer Ru(bpy)3Cl2, comparing the results to the previously reported catalysts Mn(phen)(CO)3Br and Mn(bpy)(CO)3Br. Turnover numbers (TONs) of 58 for formic acid were reached in acetonitrile with complex Mn(phdk)(CO)3(MeCN). The experiments were conducted under visible-light irradiation (λ = 480 or 500 nm) using TEOA and BNAH as sacrificial electron donors (see section SEDs below).

Advances and special progress

The efficiency of formic acid generation from CO₂ was improved compared to a previously reported manganese complex. The increased water solubility of one of the novel complexes may enable photo- or electrocatalytic CO₂ reduction in aqueous media.

Additional remarks

In electrochemical CO₂ reduction experiments, a high selectivity for CO formation was observed, contrary to the preferential formation of formic acid in the photocatalytic CO₂ reduction.

Content of the published article in detail

The article contains results for the reduction of CO₂ to formic acid under visible-light catalysis using manganese complexes as catalysts. The catalytic system performs best (referring to the TON of formic acid production) in acetonitrile using catalyst Mn(phdk)(CO)3(MeCN).

Catalyst

Mn(phdk)(CO)3Br Mn(phdk)(CO)3(MeCN) Mn(phen)(CO)3Br Mn(bpy)(CO)3Br

Photosensitizer

Ru(bpy)3Cl2

Investigation

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	.	.	.	additives	λexc [nm]	.	TON CO	TON HCOOH	.
1.	Mn(phdk)(CO)3Br		Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					480		8	52
2.	Mn(phdk)(CO)3(MeCN)		Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					480		15	58
3.	Mn(phdk)(CO)3(MeCN)		Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					480		9	48
4.	Mn(bpy)(CO)3Br		Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					480		47	15
5.	Mn(phdk)(CO)3(MeCN)		Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					500		7	40
6.	Mn(phdk)(CO)3(MeCN)		Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					457		7	34
7.	Mn(phdk)(CO)3(MeCN)	2	Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					480		5	18
8.	Mn(phdk)(CO)3(MeCN)		Ru(bpy)3Cl2	200	BNAH	0.1	MeCN					480		8	52
9.	Mn(phdk)(CO)3(MeCN)		Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					480
10.	Mn(phdk)(CO)3(MeCN)		Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					500
11.	Mn(phdk)(CO)3(MeCN)		Ru(bpy)3Cl2	100			MeCN					480		3
12.	Mn(phdk)(CO)3(MeCN)				BNAH	0.1	MeCN					500
13.	Mn(phdk)(CO)3Br		Ru(bpy)3Cl2	100	BNAH	0.1	MeCN				Argon gas	480
14.			Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					480
15.			Ru(bpy)3Cl2	100	BNAH	0.1	MeCN					480
16.	Mn(phdk)(CO)3Br		Ru(bpy)3Cl2	100	BNAH	0.1	DMF					480		21	22
17.	Mn(phdk)(CO)3Br		Ru(bpy)3Cl2	100	BNAH	0.1	DMF					480		2
18.	Mn(phdk)(CO)3Br		Ru(bpy)3Cl2	100			DMF					480		9	13
19.	Mn(phen)(CO)3Br		Ru(bpy)3Cl2	100	BNAH	0.1	DMF					480		17	4
20.	Mn(bpy)(CO)3Br		Ru(bpy)3Cl2	100	BNAH	0.1	DMF					480		6	39
21.	Mn(phdk)(CO)3(MeCN)		Ru(bpy)3Cl2	100			H2O				ascorbic acid/NaA	480
22.	Mn(phdk)(CO)3(MeCN)		Ru(bpy)3Cl2	100			H2O				ascorbic acid/NaA	500

Investigation-Name: Table 1Export

Sacrificial electron donor

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

Additives

In this study, ascorbic acid was tested as an additive and control experiments under argon atmosphere were performed.