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

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 × 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-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.