Phenoxazine-Sensitized CO2-to-CO Reduction with an Iron Porphyrin Catalyst: A Redox Properties-Catalytic Performance Study

Abstract

Summary

A photochemical reduction of CO₂ to CO was shown using the iron porphyrin complex [Fe(pTMAPP)Cl][PF6]4 as catalyst, screening the effect of different phenoxazine-based photosensitizers on the CO production. Turnover numbers (TONs) of 115 and a selectivity of 100% for CO were reached in acetonitrile in combination with the photosensitizer 100762. The experiments were conducted under visible-light irradiation (λ > 400 nm) using BIH as sacrificial electron donor (see section SEDs below).

Advances and special progress

In this study, the authors showed a strong relation between the oxidation potential of the photosensitizer and the CO production whereas no correlation between the CO production and the excited state potential of the photosensitizer was discovered. This identifies the electron transfer to regenerate the photosensitizer as a determining step and demonstrates the importance of improving the interaction between the photosensitizer and the sacrificial electron donor for optimization of the CO₂ reduction.

Additional remarks

The tested phenoxazine-based photosensitizers performed similarly in combination with the iron porphyrin complex and allowed for TONs of 88-115 and selectivities of 80-100% apart from complex 4-[7-[4-(diphenylamino)phenyl]-10-naphthalen-2-yl-phenoxazin-3-yl]-N,N-diphenyl-aniline that showed both a lower TON (32) and decreased selectivity (36%).

Content of the published article in detail

The article contains results for the reduction of CO₂ to CO under visible-light catalysis using an iron complex and different phenoxazine-based photosensitizers. The catalytic system performs best (referring to the TON of CO production) in acetonitrile.

Catalyst

[Fe(pTMAPP)Cl][PF6]4

Photosensitizer

3,7-Di((1,1'-biphenyl)-4-yl)-10-(naphthalen-1-yl)-10H-phenoxazine 1007611007621007634-[7-[4-(diphenylamino)phenyl]-10-naphthalen-2-yl-phenoxazin-3-yl]-N,N-diphenyl-aniline10-naphthalen-2-yl-3,7-di(pyren-1-yl)phenoxazine

Investigation

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	additives	.	λexc [nm]	.	TON CO	TON H2	.
1.	[Fe(pTMAPP)Cl][PF6]4	0.002	Molecule:100493	0.2	BIH	0.005	MeCN	TFE		> 400		103	25
2.	[Fe(pTMAPP)Cl][PF6]4	0.002	Molecule:100761	0.2	BIH	0.005	MeCN	TFE		> 400		88	12
3.	[Fe(pTMAPP)Cl][PF6]4	0.002	Molecule:100762	0.2	BIH	0.005	MeCN	TFE		> 400		115
4.	[Fe(pTMAPP)Cl][PF6]4	0.002	Molecule:100763	0.2	BIH	0.005	MeCN	TFE		> 400		112	12
5.	[Fe(pTMAPP)Cl][PF6]4	0.002	Molecule:100764	0.2	BIH	0.005	MeCN	TFE		> 400		32	57
6.	[Fe(pTMAPP)Cl][PF6]4	0.002	Molecule:100765	0.2	BIH	0.005	MeCN	TFE		> 400		89

Investigation-Name: Table 1Export

Sacrificial Electron Donor

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

Additives

In this study, TFE was used as an additive.