Yushu Jin

Organosilicon derivatives are important compounds in industry and valuable synthetic intermediates in organic synthesis. Direct introduction of the silicon functionality is an attractive, straightforward synthetic approach to these compounds; however, previously reported catalytic silylation of arenes has suffered from poor site-selectivity. We report that an iridium catalyst in combination with a spirobipyridine ligand selectively silylates mono- and disubstituted arenes at the meta position relative to the larger substituent. The catalyst recognizes the shape of the organic substrate through remote steric interactions to control the site-selectivity, applicable to a variety of functional groups.

Exploitation of noncovalent interactions for recognition of an organic substrate has received much attention for the design of metal catalysts in organic synthesis. The CH–π interaction is especially of interest for molecular recognition because both the C–H bonds and the π electrons are fundamental properties of organic molecules. However, because of their weak nature, these interactions have been less utilized for the control of organic reactions. We show here that the CH–π interaction can be used to kinetically accelerate catalytic C–H activation of arenes by directly recognizing the π-electrons of the arene substrates with a spirobipyridine ligand. Computation and a ligand kinetic isotope effect study provide evidence for the CH–π interaction between the ligand backbone and the arene substrate. The rational exploitation of weak noncovalent interactions between the ligand and the substrate will open new avenues for ligand design in catalysis.

A three-component hydrocarboxylation of an olefin with CO₂ and H₂ could be regarded as a dream reaction, since it would provide a straightforward approach for the synthesis of aliphatic carboxylic acids in perfect atom economy. However, this transformation has not been realized in a direct manner under mild conditions, because boosting the carboxylation with thermodynamically stable CO₂ while suppressing the rapid hydrogenation of olefin remains a challenging task. Here, we report a rhodium-catalysed reductive hydrocarboxylation of styrene derivatives with CO₂ and H₂ under mild conditions, in which H₂ served as the terminal reductant. In this approach, the carboxylation process was largely accelerated by visible light irradiation, which was proved both experimentally and by computational studies. Hydrocarboxylation of various kinds of styrene derivatives was achieved in good yields without additional base under ambient pressure of CO₂/H₂ at room temperature. Mechanistic investigations revealed that use of a cationic rhodium complex was critical to achieve high hydrocarboxylation selectivity.

Regioselective functionalization of arenes remains a challenging problem in organic synthesis. Steric interactions are often used to block sites adjacent to a given substituent, but they do not distinguish the remaining remote sites. We report a strategy based on remote steric control, whereby a roof-like ligand protects the distant para site in addition to the ortho sites, and thereby enables selective activation of meta carbon-hydrogen (C–H) bonds in the absence of ortho or para substituents. We demonstrate this concept for iridium-catalyzed meta -selective borylation of various monosubstituted arenes, including complex drug molecules. This strategy has the potential to expand the toolbox of C–H bond functionalization to previously nondifferentiable reaction sites.

Invited for this month′s cover is the group of Nobuharu Iwasawa at Tokyo Institute of Technology. The image shows a switchable site‐selective carboxylation between benzylic C−O and aryl C−Cl moieties enabled by a palladium/iridium dual catalyst under visible light irradiation. The Communication itself is available at 10.1002/cssc.202102095.

A highly efficient carboxylation of benzyl alcohol derivatives with CO₂ using a palladium/iridium dual catalyst under visible‐light irradiation was developed. A wide range of benzyl alcohol derivatives could be employed to provide benzylic carboxylic acids in moderate to high yields. Mechanistic studies indicated that the oxidative addition of benzyl alcohol derivatives was possibly the rate‐determining‐step. It was also found that a switchable site‐selective carboxylation between benzylic C−O and aryl C−Cl moieties could be achieved simply by changing the palladium catalyst.