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Photocatalysis: A Unique and Powerful Tool in Organic Synthesis

Strem offers a wide range of photocatalysts for every need in the field

A photocatalyst can be broadly defined as a material which increases its energy state upon absorption of light, and then transfers this energy to another molecule in order to facilitate a chemical reaction. Some prototypical examples of photocatalyst molecules include homoleptic Ru and Ir polypyridyl complexes, such as Ru(bpy)32+ and Ir(ppy)3 (Ru-1 and Ir-1, Figure 1). Previously, these types of complexes have been used in applications such as water splitting1, CO2 reduction2, dye-sensitized solar cells3, and as emitters in phosphorescent OLEDs4.


Figure 1. Structures of two of the most commonly utilized photocatalysts in organic transformations.

Recently, it has been discovered that these molecules can enable a variety of more complex organic transformations as well, due in part to the long lifetime and high redox potentials of their excited states. Although there are a few prior reports which use Ru(bpy)3 complexes for simple organic transformations, it was not until the last decade that photocatalysis began to garner broader interest in the synthetic organic community, fueled in part by concurrent publications from the MacMillan and Yoon groups.5,6 In 2008, Prof. David MacMillan’s group was able to demonstrate that under photolytic conditions Ru-1 could behave as both the oxidant and reductant in the enamine-catalyzed asymmetric α-alkylation of aldehydes (Figure 2). The oxidizing power of the photoexcited Ru(II)* species combined with the reducing power of the Ru(I) complex allowed for an overall redox-neutral, room-temperature radical pathway driven by light.5


Figure 2. Catalytic enantioselective α-alkylation of aldehydes using an organocatalyst and Ru-1.

Around the same time as MacMillan’s report, Prof. Tehshik Yoon’s group showed that the same Ru(bpy)3+2 complex could serve as an incredibly efficient photocatalyst for the [2 + 2] cycloaddition of enones (Figure 3).6 The reaction was proposed to operate by single electron reduction of the enone substrate by Ru(bpy)3+ formed during the reaction, allowing the substrate to undergo radical anion cycloaddition with a high degree of diastereoselectivity.


Figure 3. Catalytic [2 + 2] cycloaddition of enones using Ru-1.

Following the seminal works of MacMillan and Yoon, a number of groups became interested in using photoredox catalysis in the context of synthetic organic synthesis. As the desire for a more diverse scope of reactions increased, so too did the need for photocatalyst molecules with different properties such as oxidizing/reducing potentials, absorption properties, and excited state lifetimes. In response to this need, a number of homo- and heteroleptic Ru and Ir photocatalyst molecules have been developed, allowing chemists to tailor the properties of a catalyst for a given application. Selected examples of these catalysts and their applications will be the topic of future blog posts.

In addition to the parent structures of Ru-1 and Ir-1, Strem offers a wide variety of photocatalyst compounds of Iridium and Ruthenium containing various ligand substitutions. We also offer a number of building blocks for photocatalyst molecules, such as transition metal dimer complexes and bis-chelating aromatic ligands. The full range of catalysts and building blocks, as well as technical notes, can be found in The Strem Chemiker.7

We are continuously adding new photocatalysts to meet customer needs. Currently we offer Iridium and Ruthenium photocatalysts, screening kits and equipment. See examples in Figure 4 below.


Figure 4.  Iridium and Ruthenium Photocatalysts, available both individually and in applicable kits.
98-7500, Photochemical Equipment- PhotoRedOx Box.

See our complete Photocatalyst line here!



  1. Acc. Chem. Res. 1995, 28, 141.
  2. J. Am. Chem. Soc. 2013, 135, 14413.
  3. Coord. Chem. Rev. 1998, 177, 347.
  4. Adv. Mater. 2009, 21, 4418.
  5. Science 2008, 322, 77.
  6. J. Am. Chem. Soc. 2008, 130, 12886
  7. The Strem Chemiker Vol. XXX No. 2 



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