Light-mediated catalysis enables unique reaction pathways that were previously unattainable under thermal control and forms various unconventional bonds in synthetic organic chemistry. Among them, the most common mechanisms by which photocatalysts are capable of converting light to chemical energy with simultaneous selective molecular activation, including energy transfer, organometallic excitation, light-induced atomic transfer, and light oxidation catalysis. Ruthenium complexes with polypyridyl ligands are widely used in the field of organic synthesis as visible light photocatalysts. The classical ruthenium catalyst Ru(bpy)32+ can participate in photoredox reactions under extremely mild conditions, thereby generating free addition, deleterious side reactions hardly occur. The photocatalytic efficiency can be improved by structural modification of such complexes.
Fig. 1 Chemical structures of common Ruthenium photocatalysts.
Ruthenium catalysts are widely used in organic reactions such as reduction of electron-deﬁcient alkenes, reduction of nitrogen functional groups and oxidation of benzyl halides.
Ru(bpy)32+-mediated reduction of electron-deﬁcient alkenes was described in 1981. 1-benzyl-1,4-dihydronicotinamide (BNAH) with the redox-active 1,4-dihydropyridine unit was used as the terminal reducing agent which formed a catalyst system with catalytic quantities of Ru(bpy)32+. Dimethyl maleate as substrate undergoes free radical cleavage under visible light irradiation, and the catalytic system composed of Ru(bpy)32+ catalyzed the reduction of electron-deficient alkenes to get the saturated product dimethyl succinate.
Fig. 2 Photoredox reduction of electron-deﬁcient oleﬁns.
Ruthenium catalysts has been used for the reduction of many nitrogen-containing functional groups. For example, Ru(bpy)32+ or the related photocatalyst Ru(bpy)2(MeCN)2(PF6)2 could reduce nitrobenzenes to anilines. And the catalytic system consisting of Ru(bpy)32+, Hü nig's base and Hantzsch ester are capable of reducing azides to amines. Furthermore, Ru(bpz)32+, a tris(bipyrazyl) analogue of Ru(bpy)32+, as a powerful photoredox catalyst, can be suited for oxidatively induced photoredox transformations. N-phenyl-N-benzoylhydrazine can be reduced to N-phenylbenzamide under the catalysis of photoredox catalyst Ru(bpz)32+. In addition, N-methyl-N-phenylhydrazine can also be reduced to N-methylaniline via Ru(bpz)32+ catalysis.
Fig. 3 Reduction of nitrogen functional groups.
Pyridine derivatives as photocatalysts are able to participate in photoredox oxidation, activating α-haloester substrates to obtain α-ketoesters at room temperature. In this reaction, molecular oxygen serves as a terminal oxidant as well as the source for introducing oxygen atoms into the product. In the presence of Ru(bpy)32+ as catalyst and 4-methoxypyridine as cocatalyst, ethyl α-bromophenylacetate can be converted to ethyl benzoylformate in good yield under air. Overall, photocatalysts and organic catalysts work together to efficiently oxidize α-aryl halogen derivatives to α-aryl carbonyl compounds, which is a novel radical reaction catalyzed by pyridine derivatives.
Fig. 4 Aerobic oxidation of benzylic halides
Alfa Chemistry provides high quality Ruthenium catalysts and related services. Please don't hesitate to contact us with any questions or concerns, we are happy to provide you with more detailed services.
Please kindly note that our products and services are for research use only.
Copyright © 2023 Alfa Chemistry. All rights reserved.