Single-Site Cobalt Catalysts at New Zr8(μ2-O)8(μ2-OH)4 Metal-Organic Framework Nodes for Highly Active Hydrogenation of Alkenes, (mines, Carbonyls, and Heterocycles

We report here the synthesis of robust and porous metal-organic frameworks (MOFs), M-MTBC (M = Zr or Hf), constructed from the tetrahedral linker methane-tetrakis(p-biphenylcarboxylate) (MTBC) and two types of secondary building units (SBUs): cubic M-8(mu(2)-O)(8)(mu(2)-OH)(4) and octahedral M-6(mu(3)-O)(4)(mu(3)-OH)(4). While the M-6-SBU is isostructural with the 12-connected octahedral SBUs of UiO-type MOFs, the M-8-SBU is composed of eight M-IV ions in a cubic fashion linked by eight mu(2)-oxo and four mu(2)-OH groups. The metalation of Zr-MTBC SBUs with CoCl2, followed by treatment with NaBEt3H, afforded highly active and reusable solid Zr-MTBC-CoH catalysts for the hydrogenation of alkenes, imines, carbonyls, and heterocycles. Zr-MTBC-CoH was impressively tolerant of a range of functional groups and displayed high activity in the hydrogenation of tri- and tetra-substituted alkenes with TON > 8000 for the hydrogenation of 2,3-dimethyl-2-butene. Our structural and spectroscopic studies show that site isolation of and open environments around the cobalt-hydride catalytic species at Zr-8-SBUs are responsible for high catalytic activity in the hydrogenation of a wide range of challenging substrates. MOFs thus provide a novel platform for discovering and studying new single-site base-metal solid catalysts with enromous potential for sustainable chemical synthesis.