H/D Exchange Under Mild Conditions in Arenes and Unactivated Alkanes with C6D6 and D2O Using Rigid, Electron-rich Iridium PCP Pincer Complexes

The synthesis and characterization of an iridium polyhydride complex (Ir-H4)
supported by an electron-rich PCP framework is described. This complex readily loses molecular
hydrogen allowing for rapid room temperature hydrogen isotope exchange (HIE) at the hydridic
positions and the α-C-H site of the ligand with deuterated solvents such as benzene-d6, toluene-d8
and THF-d8. The removal of 1-2 equivalents of molecular H2 forms unsaturated iridium carbene
trihydride (Ir-H3) or monohydride (Ir-H) compounds that are able to create further unsaturation
by reversibly transferring a hydride to the ligand carbene carbon. These species are highly active
hydrogen isotope exchange (HIE) catalysts using C6D6 or D2O as deuterium sources for the
deuteration of a variety of substrates. By modifying conditions to influence the Ir-Hn speciation,
deuteration levels can range from near exhaustive to selective only for sterically accessible sites.
Preparative level deuterations of select substrates were performed allowing for procurement of
>95% deuterated compounds in excellent isolated yields; the catalyst can be regenerated by
treatment of residues with H2 and is still active for further reactions.