Robust, Chiral, and Porous BINAP-Based Metal–Organic Frameworks for Highly Enantioselective Cyclization Reactions

We report here the design of BINAP-based metal–organic frameworks and their postsynthetic metalation with Rh complexes to afford highly active and enantioselective single-site solid catalysts for the asymmetric cyclization reactions of 1,6-enynes. Robust, chiral, and porous Zr-MOFs of UiO topology, BINAP-MOF (<b>I</b>) or BINAP-dMOF (<b>II</b>), were prepared using purely BINAP-derived dicarboxylate linkers or by mixing BINAP-derived linkers with unfunctionalized dicarboxylate linkers, respectively. Upon metalation with Rh­(nbd)₂BF₄ and [Rh­(nbd)­Cl]₂/AgSbF₆, the MOF precatalysts <b>I</b>·Rh­(BF₄) and <b>I</b>·Rh­(SbF₆) efficiently catalyzed highly enantioselective (up to 99% ee) reductive cyclization and Alder-ene cycloisomerization of 1,6-enynes, respectively. <b>I</b>·Rh catalysts afforded cyclization products at comparable enantiomeric excesses (ee’s) and 4–7 times higher catalytic activity than the homogeneous controls, likely a result of catalytic site isolation in the MOF which prevents bimolecular catalyst deactivation pathways. However, <b>I</b>·Rh is inactive in the more sterically encumbered Pauson–Khand reactions between 1,6-enynes and carbon monoxide. In contrast, with a more open structure, Rh-functionalized BINAP-dMOF, <b>II</b>·Rh, effectively catalyzed Pauson–Khand cyclization reactions between 1,6-enynes and carbon monoxide at 10 times higher activity than the homogeneous control. <b>II</b>·Rh was readily recovered and used three times in Pauson–Khand cyclization reactions without deterioration of yields or ee’s. Our work has expanded the scope of MOF-catalyzed asymmetric reactions and showed that the mixed linker strategy can effectively enlarge the open space around the catalytic active site to accommodate highly sterically demanding polycyclic metallocycle transition states/intermediates in asymmetric intramolecular cyclization reactions

Robust, Chiral, and Porous BINAP-Based Metal–Organic Frameworks for Highly Enantioselective Cyclization Reactions

We report here the design of BINAP-based metal–organic frameworks and their postsynthetic metalation with Rh complexes to afford highly active and enantioselective single-site solid catalysts for the asymmetric cyclization reactions of 1,6-enynes. Robust, chiral, and porous Zr-MOFs of UiO topology, BINAP-MOF (<b>I</b>) or BINAP-dMOF (<b>II</b>), were prepared using purely BINAP-derived dicarboxylate linkers or by mixing BINAP-derived linkers with unfunctionalized dicarboxylate linkers, respectively. Upon metalation with Rh­(nbd)₂BF₄ and [Rh­(nbd)­Cl]₂/AgSbF₆, the MOF precatalysts <b>I</b>·Rh­(BF₄) and <b>I</b>·Rh­(SbF₆) efficiently catalyzed highly enantioselective (up to 99% ee) reductive cyclization and Alder-ene cycloisomerization of 1,6-enynes, respectively. <b>I</b>·Rh catalysts afforded cyclization products at comparable enantiomeric excesses (ee’s) and 4–7 times higher catalytic activity than the homogeneous controls, likely a result of catalytic site isolation in the MOF which prevents bimolecular catalyst deactivation pathways. However, <b>I</b>·Rh is inactive in the more sterically encumbered Pauson–Khand reactions between 1,6-enynes and carbon monoxide. In contrast, with a more open structure, Rh-functionalized BINAP-dMOF, <b>II</b>·Rh, effectively catalyzed Pauson–Khand cyclization reactions between 1,6-enynes and carbon monoxide at 10 times higher activity than the homogeneous control. <b>II</b>·Rh was readily recovered and used three times in Pauson–Khand cyclization reactions without deterioration of yields or ee’s. Our work has expanded the scope of MOF-catalyzed asymmetric reactions and showed that the mixed linker strategy can effectively enlarge the open space around the catalytic active site to accommodate highly sterically demanding polycyclic metallocycle transition states/intermediates in asymmetric intramolecular cyclization reactions

Cerium-Hydride Secondary Building Units in a Porous Metal–Organic Framework for Catalytic Hydroboration and Hydrophosphination

We report the stepwise, quantitative transformation of Ce^IV₆(μ₃-O)₄(μ₃-OH)₄­(OH)₆(OH₂)₆ nodes in a new Ce-BTC (BTC = trimesic acid) metal–organic framework (MOF) into the first Ce^III₆(μ₃-O)₄(μ₃-OLi)₄(H)₆(THF)₆Li₆ metal-hydride nodes that effectively catalyze hydroboration and hydrophosphination reactions. CeH-BTC displays low steric hindrance and electron density compared to homogeneous organolanthanide catalysts, which likely accounts for the unique 1,4-regioselectivity for the hydroboration of pyridine derivatives. MOF nodes can thus be directly transformed into novel single-site solid catalysts without homogeneous counterparts for sustainable chemical synthesis

Metal–Organic Frameworks Stabilize Mono(phosphine)–Metal Complexes for Broad-Scope Catalytic Reactions

Mono­(phosphine)–M (M–PR₃; M = Rh and Ir) complexes selectively prepared by postsynthetic metalation of a porous triarylphosphine-based metal–organic framework (MOF) exhibited excellent activity in the hydrosilylation of ketones and alkenes, the hydrogenation of alkenes, and the C–H borylation of arenes. The recyclable and reusable MOF catalysts significantly outperformed their homogeneous counterparts, presumably via stabilizing M–PR₃ intermediates by preventing deleterious disproportionation reactions/ligand exchanges in the catalytic cycles

Robust and Porous β‑Diketiminate-Functionalized Metal–Organic Frameworks for Earth-Abundant-Metal-Catalyzed C–H Amination and Hydrogenation

We have designed a strategy for postsynthesis installation of the β-diketiminate (NacNac) functionality in a metal–organic framework (MOF) of UiO-topology. Metalation of the NacNac-MOF (<b>I</b>) with earth-abundant metal salts afforded the desired MOF-supported NacNac-M complexes (M = Fe, Cu, and Co) with coordination environments established by detailed EXAFS studies. The NacNac-Fe-MOF catalyst, <b>I</b>•Fe­(Me), efficiently catalyzed the challenging intramolecular sp³ C–H amination of a series of alkyl azides to afford α-substituted pyrrolidines. The NacNac-Cu-MOF catalyst, <b>I</b>•Cu­(THF), was effective in promoting the intermolecular sp³ C–H amination of cyclohexene using unprotected anilines to provide access to secondary amines in excellent selectivity. Finally, the NacNac-Co-MOF catalyst, <b>I</b>•Co­(H), was used to catalyze alkene hydrogenation with turnover numbers (TONs) as high as 700 000. All of the NacNac-M-MOF catalysts were more effective than their analogous homogeneous catalysts and could be recycled and reused without a noticeable decrease in yield. The NacNac-MOFs thus provide a novel platform for engineering recyclable earth-abundant-element-based single-site solid catalysts for many important organic transformations

Photosensitizing Metal–Organic Framework Enabling Visible-Light-Driven Proton Reduction by a Wells–Dawson-Type Polyoxometalate

A simple and effective charge-assisted self-assembly process was developed to encapsulate a noble-metal-free polyoxometalate (POM) inside a porous and phosphorescent metal–organic framework (MOF) built from [Ru­(bpy)₃]²⁺-derived dicarboxylate ligands and Zr₆(μ₃-O)₄(μ₃-OH)₄ secondary building units. Hierarchical organization of photosensitizing and catalytic proton reduction components in such a POM@MOF assembly enables fast multielectron injection from the photoactive framework to the encapsulated redox-active POMs upon photoexcitation, leading to efficient visible-light-driven hydrogen production. Such a modular and tunable synthetic strategy should be applicable to the design of other multifunctional MOF materials with potential in many applications

Transformation of Metal–Organic Framework Secondary Building Units into Hexanuclear Zr-Alkyl Catalysts for Ethylene Polymerization

We report the stepwise and quantitative transformation of the Zr₆(μ₃-O)₄(μ₃-OH)₄(HCO₂)₆ nodes in Zr-BTC (MOF-808) to the [Zr₆(μ₃-O)₄(μ₃-OH)₄Cl₁₂]^6– nodes in ZrCl₂-BTC, and then to the organometallic [Zr₆(μ₃-O)₄(μ₃-OLi)₄R₁₂]^6– nodes in ZrR₂-BTC (R = CH₂SiMe₃ or Me). Activation of ZrCl₂-BTC with MMAO-12 generates ZrMe-BTC, which is an efficient catalyst for ethylene polymerization. ZrMe-BTC displays unusual electronic and steric properties compared to homogeneous Zr catalysts, possesses multimetallic active sites, and produces high-molecular-weight linear polyethylene. Metal–organic framework nodes can thus be directly transformed into novel single-site solid organometallic catalysts without homogeneous analogs for polymerization reactions

Single-Site Cobalt Catalysts at New Zr₁₂(μ₃‑O)₈(μ₃‑OH)₈(μ₂‑OH)₆ Metal–Organic Framework Nodes for Highly Active Hydrogenation of Nitroarenes, Nitriles, and Isocyanides

We report here the synthesis of a robust and porous metal–organic framework (MOF), Zr₁₂-TPDC, constructed from triphenyl­dicarboxylic acid (H₂TPDC) and an unprecedented Zr₁₂ secondary building unit (SBU): Zr₁₂(μ₃-O)₈­(μ₃-OH)₈­(μ₂-OH)₆. The Zr₁₂-SBU can be viewed as an inorganic node dimerized from two commonly observed Zr₆ clusters via six μ₂-OH groups. The metalation of Zr₁₂-TPDC SBUs with CoCl₂ followed by treatment with NaBEt₃H afforded a highly active and reusable solid Zr₁₂-TPDC-Co catalyst for the hydrogenation of nitroarenes, nitriles, and isocyanides to corresponding amines with excellent activity and selectivity. This work highlights the opportunity in designing novel MOF-supported single-site solid catalysts by tuning the electronic and steric properties of the SBUs

Single-Site Cobalt Catalysts at New Zr₈(μ₂‑O)₈(μ₂‑OH)₄ Metal-Organic Framework Nodes for Highly Active Hydrogenation of Alkenes, Imines, 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(<i>p</i>-biphenylcarboxylate) (MTBC) and two types of secondary building units (SBUs): cubic M₈(μ₂-O)₈(μ₂-OH)₄ and octahedral M₆(μ₃-O)₄(μ₃-OH)₄. While the M₆-SBU is isostructural with the 12-connected octahedral SBUs of UiO-type MOFs, the M₈-SBU is composed of eight M^IV ions in a cubic fashion linked by eight μ₂-oxo and four μ₂-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 Zr₈-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 enormous potential for sustainable chemical synthesis

Titanium(III)-Oxo Clusters in a Metal–Organic Framework Support Single-Site Co(II)-Hydride Catalysts for Arene Hydrogenation

Titania (TiO₂) is widely used in the chemical industry as an efficacious catalyst support, benefiting from its unique strong metal–support interaction. Many proposals have been made to rationalize this effect at the macroscopic level, yet the underlying molecular mechanism is not understood due to the presence of multiple catalytic species on the TiO₂ surface. This challenge can be addressed with metal–organic frameworks (MOFs) featuring well-defined metal oxo/hydroxo clusters for supporting single-site catalysts. Herein we report that the Ti₈(μ₂-O)₈(μ₂-OH)₄ node of the Ti-BDC MOF (MIL-125) provides a single-site model of the classical TiO₂ support to enable Co^II-hydride-catalyzed arene hydrogenation. The catalytic activity of the supported Co^II-hydride is strongly dependent on the reduction of the Ti-oxo cluster, definitively proving the pivotal role of Ti^III in the performance of the supported catalyst. This work thus provides a molecularly precise model of Ti-oxo clusters for understating the strong metal–support interaction of TiO₂-supported heterogeneous catalysts