Photocatalyzed Meerwein Arylation Lab Report

My presentation will focus on the photocatalysis, especially on photocatalyzed meerwein arylation. At first i would like to explain briefly what the photocatalyst means with regard to organic synthesis. It won’t be new if I say photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. The possible products and reactions mechanism could be diverse but in this type of reaction the first step is same. This is the absorption, by giving the reagent additional energy, the electron is able to move into an excited state. After excitation the molecule may return to the ground state or a lower excited state, by emitting a photon with a characteristic energy or inducing electron transfer. This previous process is that the photocatalysis

In the excited state the particle has increased oxidativ and reaductive properties. One of the most commonly used photocatalyst familiy is the transition metal complexes. In terms of photoinduced redox reactions the MLCT and LMCT transition are the most important excitation because electron from metal to ligand orbital means oxidation, electron from ligand to d orbitals means reduction respect to the metal core. Of course this excitation energy depends on the metal and also on ligands. In the photoredoxchemistry different ruthenium bipyridil complexes are widespread. This complex possesses low energy pi-star ligand orbital and by means of low oxidation state the MLCT excitation proceeds with great ease that means the oxidation process. Consequently the metal could be the oxidazing agent in the molecule and the ligand could be the reducting agent.

Last year a series of papers described applications of photocatalytic Meerwein arylations. The reason why the researchers focus on this transformation is that these are one of the most powerful synthetic tools. The aryl radicals have been widely used to create carbon−carbon. In the classical protocols the generation of aryl radicals from diazonium salts requires a catalytic or stoichiometric amount of a redox-active transition-metal salt. The reaction conditions suffered from low yields and side products. These drawbacks

The first photocatalyzed reaction with diazonium salt was reported in 1984 using [Ru(bpy)3]2+ as the photoredox catalyst under irradiation with blue light producing phenanthrene compounds. Since then, they didn’t deal with the extension of this transformation. After 30 years, this particular radical photocatalysis have attracted wide interest from researcherers with the aim to develop new synthetic pathways following the rules of green