Tunable cobalt-catalysed hydrogenation of allenes enabled by multiple metal-ligand cooperative functionalities

Catalytic hydrogenation is essential in synthetic chemistry, with ongoing innovations aimed at enhancing the selectivity and efficiency of these reactions. The hydrogenation of multisubstituted allenes, however, presents a long-standing challenge due to the difficulty of controlling multiple selectivity factors simultaneously. Here we introduce a series of chiral pincer cobalt catalysts featuring multiple metal-ligand cooperative functionalities. These catalysts feature an 'N-H' moiety as an outer-sphere binding site and an N-heterocycle group as a hemilabile basic site, enabling the use of structurally diverse tridentate ligands for selective hydrogenation of functionalized allenes. This design liberates a coordination site for H₂ activation and enhances selectivity control through the structural tuning of the N-heterocycle group. The catalysts exhibit exceptional chemo-, regio-, enantio- and Z/E-selectivities, along with broad functional group tolerance, enabling access to all possible semihydrogenation products of multisubstituted allenes. Mechanistic studies uncover a distinctive redox-neutral Co(I) catalytic cycle that facilitates heterolytic cleavage of H₂, assisted by the basic N-heterocycle on the ligand.