Carbon-carbon (C-C) bonds make up the skeleton of all organic molecules. However, creating such ubiquitous C-C bonds artificially is still a complicated task. In particular, since several molecules used in medicine, pharmacology and material chemistry contain aryl groups, devising a way to efficiently and selectively introduce this chemical group is a major goal for organic chemists. Currently, most arylation reactions require harsh reaction conditions, including high temperatures and excess additives.

Scientists at the Center for Catalytic Hydrocarbon Functionalization, within the Institute for Basic Science (IBS, South Korea), devised a method to selectively introduce aryl groups into C-H bonds at room temperature. Published in Nature Chemistry, the study also clarifies the details of this reaction, which turned out to be different from conventional wisdom.

In simple terms, the procedure consists of three main steps. First, the iridium catalyst activates the C-H containing substrate. Second, the arylsilane attacks the metal, creating an intermediate molecule. The team crystallized such intermediate and demonstrated that oxidizing the iridium center of the intermediate (third step) is beneficial to achieve a low energy arylation reaction.

The proposed reaction mechanism was verified with electro paramagnetic resonance, cyclic voltammetry and computer simulations. “Developing more efficient and environmentally benign oxidation system is our next goal,” concludes Kwangmin Shin, first author of the study.

▲ Figure 1Oxidation of the metal (M, iridium, blue pathway) leads to a 19 kcal/mol decrease in reaction’s energy barrier, and allows the arylation to occur at room temperature.

▲ Figure 2Arylation mechanism proposed by IBS researchers. The reaction proceeds through a novel pathway in which the reductive elimination takes place more easily after the intermediate is selectively oxidized.

▲ Figure 3IBS scientists were able to isolate and crystallize the reaction intermediate.

Letizia Diamante