Selective C-H Borylation of Polyaromatic Compounds Enabled by Metal-Arene π-Complexation.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Synthetic Organic Chemistry

Background:

• Undirected C-H borylation typically favors sterically accessible and acidic C-H bonds.
• Site selectivity is a major challenge in nondirected C-H borylation of polyaromatic compounds with multiple similar C-H bonds.

Purpose of the Study:

• To investigate the effect of chromium tricarbonyl π-complexation on iridium-catalyzed C-H borylation selectivity.
• To develop a strategy for achieving high site selectivity in the functionalization of polyaromatic compounds.

Main Methods:

• Utilized iridium-catalyzed C-H borylation reactions.
• Employed competition experiments to quantify reactivity differences.
• Performed density functional theory (DFT) studies to elucidate reaction mechanisms.

Main Results:

• Chromium tricarbonyl π-complexation significantly enhances C-H bond reactivity towards borylation (average two orders of magnitude faster).
• Achieved unprecedented site selectivity for C-H borylation on the π-complexed aromatic ring.
• Demonstrated room-temperature C-H borylation even with the substrate as the limiting reagent.

Conclusions:

• π-complexation with a chromium tricarbonyl unit is a powerful strategy to control site selectivity in Ir-catalyzed C-H borylation.
• The enhanced reactivity is attributed to lower activation barriers for C-H oxidative addition facilitated by chromium complexation.
• This work paves the way for developing bimetallic systems for selective C-H functionalization, leveraging noncovalent metal-arene interactions.