Metal–Organic Frameworks Stabilize Solution-Inaccessible Cobalt Catalysts for Highly Efficient Broad-Scope Organic Transformations

Abstract

New and active earth-abundant metal catalysts are critically needed to replace precious metal-based catalysts for sustainable production of commodity and fine chemicals. We report here the design of highly robust, active, and reusable cobalt-bipyridine- and cobalt-phenanthroline-based metal-organic framework (MOF) catalysts for alkene hydrogenation and hydroboration, aldehyde/ketone hydroboration, and arene C-H borylation. In alkene hydrogenation, the MOF catalysts tolerated a variety of functional groups and displayed unprecedentedly high turnover numbers of ∼2.5 × 10(6) and turnover frequencies of ∼1.1 × 10(5) h(-1). Structural, computational, and spectroscopic studies show that site isolation of the highly reactive (bpy)Co(THF)2 species in the MOFs prevents intermolecular deactivation and stabilizes solution-inaccessible catalysts for broad-scope organic transformations. Computational, spectroscopic, and kinetic evidence further support a hitherto unknown (bpy(•-))Co(I)(THF)2 ground state that coordinates to alkene and dihydrogen and then undergoing σ-complex-assisted metathesis to form (bpy)Co(alkyl)(H). Reductive elimination of alkane followed by alkene binding completes the catalytic cycle. MOFs thus provide a novel platform for discovering new base-metal molecular catalysts and exhibit enormous potential in sustainable chemical catalysis.

Chemoselective single-site Earth-abundant metal catalysts at metal–organic framework nodes

“…The very-weak-field coordination environment consisting of O-atoms that the UiO-M (M=Co, Fe) framework provides is very different than those accessible to molecular catalysts that typically consist of stronger field N- or P-donor atoms. Indeed, bipyridine and phenathroline-based MOF-Co catalysts were recently reported to be active in borylation of arene C–H bonds instead of benzylic C–H bonds52. Beyond the low coordination number, weak-field catalyst sites that lead to high electrophilicity are possible in these MOFs but are simply not available to small molecule homogeneous catalyst systems because ligands based on weakly binding O-donors would readily dissociate from first row transition metals.…”

Controlling interpenetration through linker conformation in the modulated synthesis of Sc metal–organic frameworks

“…Postsynthetic modication (PSM) in general, [53][54][55] and speci-cally metalation of chemically stable MOFs containing free bipy sites, [56][57][58][59][60][61][62] have proven to be highly efficient methods to enhance the properties of MOFs, and so we attempted metallation of 2-HCl with CuCl 2 as a proof-of-concept transformation with the aim of introducing group 10 metals for catalytic applications, as well as potentially adding suitable steric bulk to stop the material adopting a closed pore form on drying (see ESI, Section S9 †). Single crystals of 2-HCl were metallated by immersion in an anhydrous DMF solution containing CuCl 2 at 60 C for 42 hours.…”

Metal–Organic Framework Nodes Support Single-Site Magnesium–Alkyl Catalysts for Hydroboration and Hydroamination Reactions

“…We recently showed that highly active basemetal catalysts can be stabilized in bipyridyl-based MOFs via active site isolation, while analogous homogeneous catalysts undergo rapid intermolecular deactivation via ligand disproportionation reactions. 20 Herein, we report a simple strategy to stabilize active heteroleptic Mg-alkyl species at secondary building unit (SBUs) of TPHN-MOF (TPHN = 4,4′-bis-(carboxyphenyl)-2-nitro-1,1′-biphenyl) to afford highly active and reusable single-site solid catalysts for hydroboration of carbonyl and imine compounds and for hydroamination of aminoalkenes. Site isolation within the MOF stabilizes catalytically active heteroleptic Mg-alkyl species by shutting down Schlenk-type intermolecular ligand redistribution reactions ( Figure 1).…”