New Photosensitizers Based on Heteroleptic Cu(I) Complexes and CO2 Photocatalytic Reduction with (Ni(II)(cyclam))Cl2

Abstract

Summary

A photochemical reduction of CO2 was shown using the nickel catalyst Ni(cyclam)Cl2 (100812) and the copper-based photosensitizers (100906), (100907), (100908) and (100909). Turnover numbers (TONs) of 8.1 for CO were reached in acetonitrile/TEOA for complex (100908) after 4 hours. Employing the other synthesized photosensitizers (100906), (100907) or (100909), TONs of 4.3 to 4.9 were obtained. The experiments were conducted under visible-light irradiation (λ = 420 nm) using BIH as sacrificial electron donor (see section SEDs below).

Advances and special progress

The first example of Cu(I)-based photosensitizers used for photocatalytic CO2 reduction in combination with Ni(cyclam)Cl2 (100812) was successfully reported, demonstrating the usability of a fully noble-metal free CO2 reduction system. The TONs are consistent with previously reported results on noble-metal based photosensitizers.

Additional remarks

The developed heteroleptic photosensitizer complexes showed a high stability in acetonitrile and no ligand release or formation of the homoleptic complexes was detected in UV/Vis stability studies.

Content of the published article in detail

The article contains results for the reduction of CO2 to CO under visible-light catalysis using a nickel complex as catalyst and copper-based photosensitizers. The catalytic system performs best (referring to the TON of CO production) in acetonitrile/TEOA with photosensitizer (100908).

Catalysts

Ni(cyclam)Cl2 (100812)

Photosensitizers

(100906) (100907) (100908) (100909)

Investigations

		cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	.	.	.	.	λexc [nm]	.	TON CO	.	.
(edit)	1.	Ni(cyclam)Cl2	0.1	Molecule:100906	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		4.3
(edit)	2.	Ni(cyclam)Cl2	0.1	Molecule:100907	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		4.9
(edit)	3.	Ni(cyclam)Cl2	0.1	Molecule:100908	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		8.1
(edit)	4.	Ni(cyclam)Cl2	0.1	Molecule:100909	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		4.6
(edit)	5.	Ni(cyclam)Cl2	0.1	Molecule:100906	1	BIH	0.01	MeCN					420 nm (4 x 8 W)		2.6
(edit)	6.	Ni(cyclam)Cl2	0.1	Molecule:100907	1	BIH	0.01	MeCN					420 nm (4 x 8 W)		3.5
(edit)	7.	Ni(cyclam)Cl2	0.1	Molecule:100908	1	BIH	0.01	MeCN					420 nm (4 x 8 W)		5.0
(edit)	8.	Ni(cyclam)Cl2	0.1	Molecule:100909	1	BIH	0.01	MeCN					420 nm (4 x 8 W)		1.8
(edit)	9.	Ni(cyclam)Cl2	0.1	Molecule:100906	1	BIH	0.01	MeCN					420 nm (4 x 8 W)		2.8
(edit)	10.			Molecule:100908	1	BIH	0.01	MeCN					420 nm (4 x 8 W)
(edit)	11.	Ni(cyclam)Cl2	0.1	Molecule:100908	1	BIH	0.01	MeCN					420 nm (4 x 8 W)
(edit)	12.	Ni(cyclam)Cl2	0.1	Molecule:100908	1			MeCN					420 nm (4 x 8 W)
(edit)	13.	Ni(cyclam)Cl2	0.1	Molecule:100908	1	BIH	0.01	MeCN					420 nm (4 x 8 W)
(edit)	14.	Ni(cyclam)Cl2	0.1			BIH	0.01	MeCN					420 nm (4 x 8 W)
(edit)	15.	Ni(cyclam)Cl2	0.1	Molecule:100906	1	BIH	0.01	MeCN					dark
(edit)	16.	[Cu(ACN)4][BF4]	0.1	Molecule:100906	1	BIH	0.01	MeCN					420 nm (4 x 8 W)
(edit)	17.	Ni(cyclam)Cl2	0.1	Molecule:100906	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		7.3
(edit)	18.	Ni(cyclam)Cl2	0.1	Molecule:100907	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		6.5

Investigation-Name: Photocatalytic CO2 reduction and control experiments

Sacrificial Electron Donor

In this study, the experiments were done with the sacrificial electron donor BIH (100508).

Additives

In this study, TEOA (100507) was used as a proton donor. For one experiment, N(Me)3 (100910) was employed instead. The catalyst [Cu(ACN)4][BF4] (100911) was used for a control experiment.