posted on 2021-03-16, 13:37authored byNeha Antil, Ajay Kumar, Naved Akhtar, Rajashree Newar, Wahida Begum, Ashutosh Dwivedi, Kuntal Manna
The development of chemoselective
and heterogeneous earth-abundant
metal catalysts is essential for environmentally friendly chemical
synthesis. We report a highly efficient, chemoselective, and reusable
single-site nickel(II) hydride catalyst based on robust and porous
aluminum metal–organic frameworks (MOFs) (DUT-5) for hydrogenation
of nitro and nitrile compounds to the corresponding amines and hydrogenolysis
of aryl ethers 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 a 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 coordinated nitrile into the nickel-hydride bond occurring in the
turnover-limiting step. In addition, DUT-5-NiH is also an active catalyst
for chemoselective hydrogenolysis of carbon–oxygen bonds in
aryl ethers to afford hydrocarbons under atmospheric hydrogen in the
absence of any base, which is important for the generation of fuels
from biomass. This work highlights the potential of MOF-based single-site
earth-abundant metal catalysts for practical and eco-friendly production
of chemical feedstocks and biofuels.