Pyranopterin Related Dithiolene Molybdenum Complexes as Homogeneous Catalysts for CO2 Photoreduction

Abstract

Summary

A photochemical reduction of CO₂ to formic acid or CO was shown using the novel dithiolene molybdenum complexes [K]2[MoO(Hqpdt)2] and [MoO(2Hqpdt)2][NBu4] in comparison to the previously reported complex [MoO(qpdt)2][NBu4]2 as catalysts in combination with photosensitizer Ru(bpy)3Cl2. Turnover numbers (TONs) of up to 83 for formic acid and 40 for CO were reached in acetonitrile for complex [MoO(2Hqpdt)2][NBu4]. The experiments were conducted under visible-light irradiation (λ = 400 nm) using BIH and TEOA as sacrificial electron donor (see section SEDs below).

Advances and special progress

Bioinspired dithiolene Mo-complexes as analogues of the active site of the FDH (formate dehydrogenase) were shown to be active as CO₂ photoreduction catalysts with formation of formic acid as the main product.

Additional remarks

The developed complex [MoO(2Hqpdt)2][NBu4] shows a similar TON for formic acid production to the previously synthesized complex [MoO(qpdt)2][NBu4]2, however a strong increase in selectivity is observed. The previously reported complex mainly catalyzes the generation of hydrogen.

Content of the published article in detail

The article contains results for the reduction of CO₂ to CO or formic acid under visible-light catalysis using molybdenum complexes and a ruthenium-based photosensitizer. The catalytic system performs best (referring to the TON of formic acid production) in acetonitrile with complex [MoO(2Hqpdt)2][NBu4].

Catalyst

[K]2[MoO(Hqpdt)2] [MoO(2Hqpdt)2][NBu4] [MoO(qpdt)2][NBu4]2

Photosensitizer

Ru(bpy)3Cl2

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	.
1.	[MoO(qpdt)2][NBu4]2	0.05	Ru(bpy)3Cl2	0.5	BIH	0.1	MeCN				400		73	670	80
2.	[K]2[MoO(Hqpdt)2]	0.05	Ru(bpy)3Cl2	0.5	BIH	0.1	MeCN				400		13	51	31
3.	[MoO(2Hqpdt)2][NBu4]	0.05	Ru(bpy)3Cl2	0.5	BIH	0.1	MeCN				400		40	89	83

Experiment-Name: Table 1Export

Sacrificial Electron Donor

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

Additives

In this study, no additives were tested.