Dehydrogenation of amine–boranes catalyzed by a $\mathrm{PC}_{sp^3}\mathrm{P}$ pincer iridium complex

Dibenzobarrelene-based $\mathrm{PC}_{sp^3}\mathrm{P}$ pincer iridium complex bearing dangling $\mathrm{CH_{2}OH}$ groups, $(\mathrm{PC}_{sp^3}\mathrm{P^{CH_{2}OH}})\mathrm{IrH(Cl)}$, catalyzes the dehydrogenation of amine–boranes at the reaction rate changing counter intuitively in the order: $\mathrm{Me_2NH \cdot BH_3 > Bu^t NH_2 \cdot BH_3 > NH_3 \cdot BH_3}$. The spectral (IR and NMR) data and DFT/M06 calculations have revealed that the binding of amine–boranes to the dangling OH group leads to an additional stabilization of the $\mathrm{Ir \cdots OH}$ bond, thus hampering the dehydrogenation reaction, whereas the amine–borane coordination to iridium entails a fac- to mer-transformation of the complex and initiates the catalytic $\mathrm{H_2}$ evolution.