Alternative Conceptual Approach to the Design of Bifunctional Catalysts: An Osmium Germylene System for the Dehydrogenation of Formic Acid

The reaction of the hexahydride OsH6(PiPr3)2 with a P,Ge,P-germylene-diphosphine
affords
an osmium tetrahydride derivative bearing a Ge,P-chelate, which arises
from the hydrogenolysis of a P–C­(sp3) bond. This
Os­(IV)–Ge­(II) compound is a pioneering example of a bifunctional
catalyst based on the coordination of a σ-donor acid, which
is active in the dehydrogenation of formic acid to H2 and CO2. The kinetics
of the dehydrogenation, the characterization of the resting state
of the catalysis, and DFT calculations point out that the hydrogen
formation (the fast stage) exclusively occurs on the coordination
sphere of the basic metal center, whereas both the metal center and
the σ-donor Lewis acid cooperatively participate in the CO2 release (the rate-determining step). During the process,
the formate group pivots around the germanium to approach its hydrogen
atom to the osmium center, which allows its transfer to the metal
and the CO2 release.