Title: Aluminum metal-organic framework nodes support single-site nickel (II)-hydride catalyst for chemoselective hydrogenation of nitro and nitrile compounds

Abstract

The development of chemoselective and heterogeneous earth-abundant metal catalysts is essential for environment-friendly chemical synthesis. We report a highly efficient, chemoselective and reusable single-site nickel(II) hydride catalyst based on a robust and porous aluminum metal-organic frameworks (DUT-5) for hydrogenation of nitro and nitrile compounds to the corresponding amines under mild conditions. The nickel hydride catalyst was prepared by the metalation of aluminum hydroxide secondary building units (SBUs) of DUT-5 having the formula of Al(µ2-OH)(bpdc) (bpdc = 4,4’-biphenyldicarboxylate) with NiBr2 followed by the reaction with NaEt3BH. DUT-5-NiH has a broad substrate scope with excellent functional group tolerance in the hydrogenation of aromatic and aliphatic nitro and nitrile compounds under 1 bar H2, and could be recycled and reused at least 10 times. By changing the reaction conditions of the hydrogenation of nitriles, symmetric or unsymmetric secondary amines were also afforded selectively. The experimental and computational studies suggested reversible nitrile coordination to nickel followed by 1,2-insertion of the coordinated nitrile into nickel-hydride bond occurring in the turnover limiting step. The zeroth-order dependence of the reaction rate on the pressure of H2 allowed progressing all the reactions under ambient hydrogen pressure. This work highlights the potential of MOF-based single-site earth-abundant metal catalysts for practical and eco-friendly chemical feedstocks production due to their low cost, excellent stability and reactivity, and the usage of cheap and atom-economical reductant hydrogen.