Metal-organic frameworks (MOFs) provide highly designable platforms to construct complex coordination architectures for targeted applications. Herein, we demonstrate that trans-coordinated metal centers with exposed equatorial positions can be placed in a MOF matrix. A Zr-based MOF, namely, PCN-160, was initially synthesized as a scaffold structure. Postsynthetic linker labilization was subsequently implemented to partially remove the original dicarboxylate linkers and incorporate pyridinecarboxylates. A pair of neighboring pyridyl groups was arranged at proper proximity within the framework to form trans-binding sites that accommodate different metal cations including Mn, Fe, Co, Ni, Cu, and Pd. Furthermore, the trans-coordinated Ni sites in porous frameworks can be readily accessed by substrates along the equatorial plane, facilitating the catalysis as manifested by the superior activity in ethylene dimerization over that observed for a cis-chelated catalyst.
The coordination-driven self-assembly of an anthracene-functionalized ditopic pyridyl donor and a tetracene-based dinuclear Ru(II) acceptor resulted in an interlocked metalla[2]catenane, [M2L2]2, in methanol and a corresponding monorectangle, [M2L2], in nitromethane. Subsequently, guest template, solvent, and concentration effects allowed the self-assembly to be reversibly fine-tuned among monorectangle and catenane structures.
Metal−organic frameworks (MOFs) provide highly versatile platforms to stabilize molecular catalysts that are not readily accessible under homogeneous conditions, thus enabling access to a new set of catalytic materials. Herein, we describe a recyclable and highly active nickel catalyst immobilized on MOF for Suzuki−Miyaura coupling reaction, which operates under mild conditions. This mixed ligand catalyst forms from the combination of 1 equiv of MOFimmobilized ligand, 1 equiv of nickel source, and 1 equiv of PPh 3 . The nature of the catalyst was verified through a series of analytical tests and catalysis experiments. The immobilized catalyst was reusable for at least up to 7 cycles without decrease in the yield of the coupled product. We also verified that this reaction does not work under homogeneous conditions and that the reaction is truly heterogeneous through "hot filtration" experiments. We identified that the reaction is first order in arylborane concentration and negative order in arylbromide concentration through the effect of substrate concentrations on the initial rate. This informed us to conduct the catalysis under slow addition of the arylbromide and reduce the catalyst loading to 1% from 3%, without detriment to the yield or rate of the reaction. The catalyst gave good to excellent isolated yields with a range of functionalities, including heterocycles on aryl bromide with widely varying electronic properties.
Reaction of cis-[Cl(2)Pt(S(O)Me(2))(2)] with 1 equiv of sym-N,N',N″-triarylguanidines, ArN═C(NHAr)(2) (sym = symmetrical; Ar = 2-MeC(6)H(4) (LH(2)(2-tolyl)), 2-(MeO)C(6)H(4) (LH(2)(2-anisyl)), 4-MeC(6)H(4) (LH(2)(4-tolyl)), 2,5-Me(2)C(6)H(3) (LH(2)(2,5-xylyl)), and 2,6-Me(2)C(6)H(3) (LH(2)(2,6-xylyl))) in toluene under reflux condition for 3 h afforded cis- or trans-[Cl(2)Pt(S(O)Me(2))(ArN═C(NHAr)(2))] (Ar = 2-MeC(6)H(4) (1), 2-(MeO)C(6)H(4) (2), 4-MeC(6)H(4) (3), 2,5-Me(2)C(6)H(3) (4), and 2,6-Me(2)C(6)H(3) (5), respectively) in 83-96% yield. Reaction of cis-[Cl(2)Pt(S(O)Me(2))(2)] with 1 equiv of LH(2)(2-tolyl) and LH(2)(4-tolyl) in the presence of 1 equiv of NaOAc in methanol under reflux condition for 3 h afforded acetate-substituted products, cis-[(AcO)ClPt(S(O)Me(2))(ArN═C(NHAr)(2))] (Ar = 2-MeC(6)H(4) (6) and 4-MeC(6)H(4) (7)) in 83% and 84% yields, respectively. Reaction of cis-[Cl(2)Pt(S(O)Me(2))(2)] with 1 equiv of LH(2)(2-anisyl) and LH(2)(2-tolyl) in the presence of 1 equiv of NaOAc in methanol under reflux condition for 3 and 12 h afforded six-membered [C,N] platinacycles, [Pt{κ(2)(C,N)-C(6)H(3)R-3(NHC(NHAr)(═NAr))-2}Cl(S(O)Me(2))] (Ar = 2-RC(6)H(4); R = OMe (8) and Me (9)), in 92% and 79% yields, respectively. The new complexes have been characterized by analytical and spectroscopic techniques, and further the molecular structures of 1, 2, 4, 5, 6, and 8 have been determined by single-crystal X-ray diffraction. The platinum atom in 1, 4, and 5 exhibited the trans configuration, while that in 2, 6, and 8 exhibited the cis configuration. Complex 6 is shown to be the precursor for 9, and the former is suggested to transform to the latter possibly via an intramolecular C-H activation followed by elimination of AcOH. The solution behavior of new complexes has been studied by multinuclear NMR ((1)H, (195)Pt, and (13)C) spectroscopy. The new complexes exist exclusively as a single isomer (trans (1 and 5) and cis (6 and 7)), a mixture of cis and trans isomers with the former isomer being predominant in the case of 2 and the latter isomer being predominant in the case of 3. Complex 5 in the trans form revealed the presence of one isomer at 0.007 mM concentration and two isomers in about 1.00:0.12 ratio at 0.154 mM concentration as revealed by (1)H NMR spectroscopy, and this has been ascribed to the restricted Pt-S bond rotation at higher concentration. Platinacycle 8 exists as one isomer, while 9 exists as a mixture of seven isomers in solution. The influence of steric factor, π-acceptor property of the guanidine, subtle solid-state packing forces upon the configuration of the platinum atom, and the number of isomers in solution have been outlined. Factors that accelerate or slow down the cycloplatination reaction, the role of NaOAc, and a plausible mechanism of this reaction have been discussed.
Sites isolation of active metals centers, systematically studied in homogeneous systems, has been an alternative to develop low metal consuming, highly active next generation catalysts in heterogeneous condition. Because of the high porosity and facile synthetic procedures, MOF-based catalysts are excellent candidates for heterogenization of well-defined homogeneous catalysts. Herein, we report the direct Pd coordination on the azobenzene linker within a MOF catalyst through a postsynthetic modification method for a Suzuki−Miyaura coupling reaction. The immobilized cyclopalladated complexes in MOFs were analyzed by a series of characterization techniques including XPS, PXRD, and deuterium NMR ( 2 H NMR) spectroscopy. The heterogeneous nature of the catalyst as well as its stability were demonstrated though "hot filtration" and recycling experiments. Furthermore, we demonstrate that the MOF packed column promoted the reaction between phenyl boronic acid and bromobenzene under microflow conditions with a 85% yield continuously for 12 h. This work sheds light on the potential of site-isolated MOF catalysts in efficient, recyclable and continuous flow systems for industrial application.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.