Schematic showing the beneficial effects of active site isolation in MOFs: while homogeneous catalysts undergo intermolecular deactivation via ligand disproportionation/decomposition reactions, such pathways are completely shut down in MOFs due to active site isolation. MOFs thus provide a new platform for discovering novel base-metal molecular catalysts.
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 cobaltbipyridine- 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 × 106 and turnover frequencies of ∼1.1 × 105 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•−)CoI (THF)2 ground state that coordinates to alkene and dihydrogen and then undergoing σ-complexassisted 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.
Teng Zhang, Kuntal Manna, and Wenbin Lin*
Department of Chemistry, University of Chicago, 929 E. 57th Street, Chicago, Illinois 60637, United States
J. Am. Chem. Soc., 2016, 138 (9), pp 3241–3249
Publication Date (Web): February 11, 2016