Reversible Hydrogen Activation by a Pyridonate Borane Complex: Combining Frustrated Lewis Pair Reactivity with Boron‐Ligand Cooperation

Abstract

A pyridone borane complex that liberates dihydrogen under mild conditions is described. The reverse reaction, dihydrogen activation by the formed pyridonate borane complex, is achieved under moderate H pressure (2 bar) at room temperature. DFT and DLPNO-CCSD(T) computations reveal that the active form of the pyridonate borane complex is a boroxypyridine that can be described as a single component frustrated Lewis pair (FLP). Significantly, the boroxypyridine undergoes a chemical transformation to a neutral pyridone donor ligand in the course of the hydrogen activation. This unprecedented mode of action may thus, in analogy to metal-ligand cooperation, be regarded as an example of boron-ligand cooperation.

Semihydrogenation of Alkynes Catalyzed by a Pyridone Borane Complex: Frustrated Lewis Pair Reactivity and Boron–Ligand Cooperation in Concert

“…gen activation by 3 requires af ree activation energy of 19.4 kcal mol À1 .T his elementary step is according to our computations thermoneutral, which agreesw ith the previously observed facile reversibility of the hydrogen activation. [7] The free energy change that is associated with the dissociation of 4 into Piers borane 6 and the pyridone 5 is 16.8 kcal mol À1 .R elaxed potential energy surface scans indicatet hat the dissociation is barrierless.A st he experimental results indicate that the bispyridonec omplex 8 is the resting state of the transformation, we consideredt he coordinationo ft he free pyridone 5 to the boroxypyridine 3.I ndeed,t he formationo f8 is according to the computations exergonic. The hydroboration of the model substrate 2-butyne requires am oderate activation energy of 4.9 kcal mol À1 and yields the alkenylborane 11.T he bispyridonec omplex 8 together with 11 is the restings tate of the catalytic transformation.…”

Hydrogenation of CO2 to Formate with H2: Transition Metal Free Catalyst Based on a Lewis Pair

“…1.65 Å in BCF/pyridines) and longer than that of the B−O single bond in pure organic system (e.g. 1.36 Å in pyridonate borane complex).…”

Element‐Ligand Cooperativity with p‐Block Elements

“…Gellrich further expanded the pyridine‐based BLC chemistry with the synthesis of boroxypyridine 9 ‐open , which is in equilibrium with its intramolecular Lewis adduct 9 ‐closed (Figure b) . 9 ‐open reversibly activated dihydrogen via BLC, leading to the pyridone borane adduct 10 .…”