Triptycene-based Ligand Research Articles

Zn-based Metal-Organic Frameworks Using Triptycene Hexacarboxylate Ligands: Synthesis, Structure, and Gas-Sorption Properties.

A series of metal-organic frameworks (MOFs) based on zinc ions and two triptycene ligands of different size were synthesized under solvothermal conditions. The structural analyses revealed that these are isostructural three-dimensional-network MOFs. The high porosity and thermal stability of these MOFs can be attributed to the highly rigid triptycene-based ligands. Their BET specific surface areas depend on the size of the triptycene ligands. In contrast to these surface-area data, the H2 and CO2 adsorption of these MOFs is larger for MOFs with small pores. Consequently, we introduced functional groups to the bridge-head position of the triptycene ligands and investigated their effect on the gas-sorption properties. The corresponding results unveiled the role of the functional groups in the specific CO2 binding via an induced interaction between adsorbates and the functional groups. Excellent H2 and CO-2 properties in these MOFs were achieved in the absence of open metal sites.

Ideal trigonal prismatic coordination geometry of Co(II) in a honeycomb MOF with a triptycene-based ligand.

A metal-organic framework (MOF) comprised of cobalt ions and triptycene-based 3-fold symmetric bridging ligands 9,10-[1,2]benzenoanthracene-2,3,6,7,14,15(9H,10H)-hexaone (o-TT) was prepared. Single-crystal structure analysis revealed a 2D honeycomb network structure and the ideal trigonal prismatic geometry of the Co(II) ion. The magnetic anisotropy of the Co(II) ion in the trigonal prism coordination geometry was analyzed via magnetic measurements and model calculations.

Reticular Chemistry for Highly Porous Metal-Organic Frameworks: The Chemistry and Applications.

Current global crises related to clean energy and the environment entail the development of materials that are capable of addressing these challenges. Metal-organic frameworks (MOFs), a class of functional materials assembled from metal-containing nodes and organic ligands via coordination bonds, have been successfully developed for various applications, including catalysis, toxic chemical removal, and gas storage and separation, as a result of their highly tailorable nature and precisely engineered pore structures. In particular, the exceptionally high surface areas and porosities of MOFs are two of their most attractive characteristics and place them among the best porous materials for the storage of clean energy gases, such as hydrogen and methane. Reticular chemistry stands out as a prominent approach to the design of MOFs as this strategy allows for the rational top-down design of frameworks guided by topological nets to afford extended framework structures with precise architectural arrangements at the molecular level. Bridging the gap between reticular chemistry design strategies and highly porous MOFs can facilitate the development of next-generation high-performance materials through state-of-the-art chemical design.In this Account, we summarize our group's efforts over the past few years toward the synthesis and applications of highly porous MOFs inspired by reticular chemistry. First, we describe how we leveraged reticular chemistry to synthesize NU-1500, which is based on the 6-connected edge-transitive acs net, from the assembly of triptycene-based ligands and high-valent metal trimers. This delicate design is amenable to isoreticular expansion, and including an additional phenyl group in the rigid triptycene-based ligand of NU-1500 yields NU-1501. Importantly, NU-1501-Al exhibits both a high gravimetric Brunauer-Emmett-Teller (BET) area of 7310 m2 g-1, which is the current record after satisfying the four BET consistency criteria, and a volumetric BET area of 2060 m2 cm-3. The high porosity and surface area place NU-1501 among the most promising adsorbents for the storage of methane and hydrogen. Second, we illustrate the rational synthesis of highly porous and stable Zr-MOFs based on edge-transitive nets: (1) the successful isoreticular expansions of NU-1000 (a 4,8-connected csq net) form hierarchical mesoporous MOFs with pore sizes of up to 6.7 nm; (2) the assembly of Zr6 clusters and tetracarboxylates yields the NU-1100 series (4,12-connected ftw net) with BET areas of 4300-6500 m2 g-1; and (3) the use of hexacarboxylates in combination with Zr6 clusters results in the formation of the NU-1600 series (a 6,12-connected alb net) with BET areas of 2000-4500 m2 g-1. Third, we leveraged a reticular exploration strategy to access mesoporous uranium-based MOFs, NU-1300 (a 3,4-connected tbo net, 2100 m2 g-1) and NU-1301 (a 3-connected nun net, 4750 m2 g-1). In particular, we investigated the structurally complex NU-1301, which formed serendipitously from the combination of uranyl clusters and triangular carboxylates to afford a structure with the largest unit cell among all reported MOFs.Finally, we provide an overview of potential applications of these highly porous MOFs, including water capture, catalysis, methane storage, hydrogen storage, and the separation of organic dyes and biological macromolecules. We hope that this Account may serve as a blueprint and stimulate researchers to develop the next generation of highly porous materials for energy- and environment-related applications and beyond.

Long-Lived C60 Radical Anion Stabilized Inside an Electron-Deficient Coordination Cage.

Fullerene C60 and its derivatives are widely used in molecular electronics, photovoltaics, and battery materials, because of their exceptional suitability as electron acceptors. In this context, single-electron transfer on C60 generates the C60• - radical anion. However, the short lifetime of free C60• - hampers its investigation and application. In this work, we dramatically stabilize the usually short-lived C60• - species within a self-assembled M2L4 coordination cage consisting of a triptycene-based ligand and Pd(II) cations. The electron-deficient cage strongly binds C60 by providing a curved inner π-surface complementary to the fullerene's globular shape. Cyclic voltammetry revealed a positive potential shift for the first reduction of encapsulated C60, which is indicative of a strong interaction between confined C60• - and the cationic cage. Photochemical one-electron reduction with 1-benzyl-1,4-dihydronicotinamide allows selective and quantitative conversion of the confined C60 molecule in millimolar acetonitrile solution at room temperature. Radical generation was confirmed by nuclear magnetic resonance, electron paramagnetic resonance, ultraviolet-visible-near-infrared spectroscopy and electrospray ionization mass spectrometry. The lifetime of C60• - within the cage was determined to be so large that it could still be detected after one month under an inert atmosphere.

Synthesis of rigid chiral C3-symmetric triptycene-based ligands and their application in enantioselective Cu(I)-catalyzed aziridination of chalcones

The design and synthesis of C3- symmetric or pseudo-C3-symmetric ligands present a particular challenge because the molecular frames available for fitting C3 symmetry are rare. Herein, we report on the synthesis and characterization of new C3-symmetric tripodal TripTOX ligands, based on the rigid triptycene backbone, and on their successful application in the asymmetric copper-catalyzed aziridination reaction. The ligand showed good to excellent performance in the copper-catalyzed asymmetric aziridination of chalcones. The catalyst derived from the new ligand appears to be the catalyst of choice when substrates have a coordinating nature.

Design and Synthesis of a Novel Triptycene-Based Ligand for Modeling Carboxylate-Bridged Diiron Enzyme Active Sites

A novel triptycene-based ligand with a preorganized framework was designed to model carboxylate-bridged diiron active sites in bacterial multicomponent monooxygenase (BMM) hydroxylase enzymes. The synthesis of the bis(benzoxazole)-appended ligand L1 depicted was accomplished in 11 steps. Reaction of L1 with iron(II) triflate and a carboxylate source afforded the desired diiron(II) complex [Fe(2)L1(μ-OH)(μ-O(2)CAr(Tol))(OTf)(2)].

Cyclometalated phosphine-based Ir(III) pincer complex as a catalyst for Oppenauer-type oxidation of alcohols

Abstract Transfer dehydrogenation of ketones was efficiently carried out in acetone under air by means of a new Ir(III)-cyclometalated pincer type catalyst bearing a robust triptycene-based ligand.

Synthesis and Structural Investigation of New Triptycene-Based Ligands: En Route to Shape-Persistent Dendrimers and Macrocycles with Large Free Volume

Triptycene was used to build a series of ligands containing pyrazine groups for use in forming coordination frameworks and as model compounds toward target shape-persistent dendrimers and macrocycles. The phenylenediamine precursors are formed by controlled double nitration/reduction of triptycene, followed by condensation with triptycenyl o-quinone to form the ligands. Solid-state structures show that the ligands favor packing in layered structures with intermolecular pi stacking. Increasing the length of the wings still allows for effective packing, but increasing the number of pyrazine groups or adding more triptycenyl moieties reduces packing efficiency. To demonstrate the potential of these molecules to function as ligands, a coordination complex of 15 with copper(I) iodide was obtained and found to form dimers that pack into a layered arrangement.

Rigid trans-spanning triptycene-based ligands: How flexible they can be?

trans-[1,8-Bis(diisopropylphosphino)triptycene]nickel (II) dichloride, trans-[1,8-bis(diisopropylphosphino)triptycene]carbonylrhodium (I) chloride and cis-[1,8-bis(diisopropyl-phosphino)triptycene] platinum (II) dichloride have been prepared and fully characterized in order to evaluate the coordination diversity of triptycene-based bidentate ligands. Their structural features and coordination preferences were studied and compared to the previously reported palladium complexes. The comparative structural analysis revealed that 1,8-bis(diisopropylphosphino)triptycene is able to access a variety of bite angles and to stabilize metal centers in different geometries. In addition, intramolecular weak C–H⋯Cl–Pt hydrogen bonding interactions which stabilize [1,8-bis(diisopropyl-phosphino)triptycene] platinum (II) dichloride in a constrained cis form are discussed.

Roof-Shaped Halide-Bridged Bimetallic Complexes via Ring Expansion Reaction

Binucleating behavior of rigid triptycene-based ligands has been studied. It has been demonstrated that trans-spanned transition-metal mononuclear complexes bearing 1,8-bis(diisopropylphosphino)triptycene (L1) and 1-diisopropylphosphino-8-diphenylphosphinotriptycene (L2) react with an appropriate transition-metal precursor via a ring-expansion pathway to form unusual bimetallic quasi-closed structures. New palladium and rhodium complexes featuring strongly bent (ca. 115 degrees ) M2(mu-Cl2) cores with very closely spanned metal centers (less than 3 A) have been prepared using the described ring-expansion reaction and have been fully characterized. Despite a constrained arrangement of the binuclear system, halogen bridges in all new compounds were stable in both the solid state and solution showing no tendency for dissociation even in the presence of added Lewis bases. Spontaneous resolution of the dissymmetric Pd2(mu-Cl)2Cl2(1-diisopropylphosphino-8-diphenylphosphinotriptycene) (2) into enantiopure antipodes is discussed as well.