Abstract
Earth-abundant metal catalysts are critically needed for sustainable chemical synthesis. Here we report a simple, cheap and effective strategy of producing novel earth-abundant metal catalysts at metal–organic framework (MOF) nodes for broad-scope organic transformations. The straightforward metalation of MOF secondary building units (SBUs) with cobalt and iron salts affords highly active and reusable single-site solid catalysts for a range of organic reactions, including chemoselective borylation, silylation and amination of benzylic C–H bonds, as well as hydrogenation and hydroboration of alkenes and ketones. Our structural, spectroscopic and kinetic studies suggest that chemoselective organic transformations occur on site-isolated, electron-deficient and coordinatively unsaturated metal centres at the SBUs via σ-bond metathesis pathways and as a result of the steric environment around the catalytic site. MOFs thus provide a novel platform for the development of highly active and affordable base metal catalysts for the sustainable synthesis of fine chemicals.
Highlights
Earth-abundant metal catalysts are critically needed for sustainable chemical synthesis
Built out of metal cluster secondary building units (SBUs) and organic linkers, metal–organic framework (MOF) have been explored as useful molecular materials for many potential applications, including gas storage[5,6], separation[7,8], catalysis[9,10], sensing[11,12,13], biomedical imaging[14], drug delivery[15], solar energy harvesting[16] and conductivity[17,18]
The deprotonation of m3–OH sites of MOFs SBUs followed by reactions with iron- and cobalt-halides afforded Fe- and Co-functionalized MOF-materials for a broad scope of organic transformations (Fig. 3)
Summary
Earth-abundant metal catalysts are critically needed for sustainable chemical synthesis. The straightforward metalation of MOF secondary building units (SBUs) with cobalt and iron salts affords highly active and reusable single-site solid catalysts for a range of organic reactions, including chemoselective borylation, silylation and amination of benzylic C–H bonds, as well as hydrogenation and hydroboration of alkenes and ketones. The simplest and most common method of producing single-site heterogeneous catalysts is to anchor catalytically active atoms, ions or molecular complexes to high surface area solid supports, such as silica or other robust metal oxides. We attempt to use inorganic oxide clusters that are well positioned and separated in porous metal–organic frameworks (MOFs) to design highly active earth-abundant metal-based single-site solid catalysts. The straightforward and cost-effective metalation of SBUs of UiO-MOFs with readily available cobalt and iron precursors affords highly electrondeficient and coordinatively unsaturated metal centres that can catalyse interesting organic reactions We believe this occurs via s-bond metathesis reaction pathways. We have discovered the first example of catalytic undirected sp[3] C–H silylation with alkoxysilane using the Co@SBU catalyst
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