H/D exchange under mild conditions in arenes and unactivated alkanes with CDand DO using rigid, electron-rich iridium PCP pincer complexes.

Abstract

An iridium polyhydride complex bearing an electron-rich PCP pincer ligand was synthesized and fully characterized. At room temperature, the complex readily releases molecular hydrogen, enabling rapid hydrogen isotope exchange (HIE) at hydridic and α-C-H positions with deuterated solvents. Sequential loss of one or two equivalents of H2 generates unsaturated iridium carbene trihydride or monohydride intermediates capable of reversible hydride transfer to the carbene carbon, creating additional coordinative unsaturation. These intermediates function as highly active HIE catalysts using CD4 or D2O as deuterium sources, enabling deuteration of diverse substrates including arenes and unactivated alkanes. Reaction conditions can be tuned to achieve either exhaustive or sterically selective deuteration. Preparative-scale deuterations afforded target compounds with greater than 95% deuterium incorporation in excellent isolated yields. The catalyst is recoverable and remains active after regeneration by treatment with H2.

Mechanism

The iridium PCP pincer complex releases H2 to form unsaturated carbene intermediates that undergo reversible oxidative addition and reductive elimination at substrate C-H bonds, using CD4 or D2O as deuterium sources to catalyze hydrogen isotope exchange.