Selective H/D Exchange of Pyridines and Alkylarenes with D₂ Enabled by a Heterometallic Mg-Ni-Mg Polyhydride Complex

Heterometallic polyhydride complexes containing main-group metals and transition metals have attracted much attention due to their versatile MH_n units and potential metal-metal synergies for molecular transformation. In this work, we report that a heterometallic Mg-Ni-Mg polyhydride complex [(LMg)₂NiH₄] {L = [(DippNCMe)₂CH]^-, Dipp = 2,6-ⁱPr₂C₆H₃} is able to catalyze the selective H/D exchange of ortho C(sp²)-H bonds of pyridine derivatives with D₂ to obtain deuterium-labeled compounds with high isotopic incorporation. Moreover, benzylic C(sp³)-H bonds are also successfully labeled using D₂ in the presence of [(LMg)₂NiH₄]. Pharmaceuticals with high isotopic incorporation have also been achieved with this catalytic system. Stoichiometric reactions of [(LMg)₂NiH₄] with pyridines yield the Mg-Ni cooperative mono- and bis-ortho C-H bond activation complexes, i.e., trihydride [(LMg)₂NiH₃(NC₅H₄R)(NC₅H₃R)] (R = Ph, Et) and dihydride [(LMg)₂NiH₂(NC₅H₃Ph)₂], which are considered as active intermediates in the catalytic process.