Multifunctional Catalysis by a One-Dimensional Copper(II) Metal Organic Framework Containing Pre-existing Coordinatively Unsaturated Sites: Intermolecular C–N, C–O, and C–S Cross-Coupling; Stereoselective Intramolecular C–N Coupling; and Aziridination Reactions

Abstract

The coordinatively unsaturated sites (CUS) are vital in metal-centered catalysis. Metal–organic frameworks (MOFs) provide a unique opportunity to generate and stabilize CUS due to their robust structure. Generally, the generation of CUS in MOFs needs prior activation under heat and high vacuum to remove labile molecules occupying the catalytic sites. Herein, we report a solvothermal synthesis of a ready-to-use copper MOF containing accessible pre-existing CUS that does not need activation. The single crystal X-ray diffraction structure reveals a square planar Cu­(II) center with two N-methylimidazoles (Mim) and one benzenedicarboxylic acid (BDC) with the formula unit [CuII(BDC)­(Mim)2] n (Cu-1D) forming an infinite one-dimensional (1D) chain along the c axis. The 1D chains are stabilized by noncovalent π–π, CH···π, and H-bonding interaction to give 2D (sheet-like) and 3D networks in the solid state. The quantification of non-covalent interaction is studied by Hirshfeld surface analysis, and the formation of a higher architecture in the solid state is confirmed by SEM analysis. The reported Cu-1D MOF acts as a solid heterogeneous catalyst and exhibits efficient catalytic activity in intermolecular and intramolecular cross-coupling reactions. Intermolecular C-heteroatom cross-coupling of a variety of N-heterocycles, aliphatic, aromatic, alicyclic amines and amides (C–N), phenols (C–O), and thiols (C–S) with aryl halides (halide = I, Br) was achieved with 70 to 95% yield, better than the state-of-the-art Cu-based homogenous system. The C–N coupling catalytic cycle is initiated by the in situ reduction of Cu­(II) by KOH/DMSO to Cu­(I) species. Subsequently, Cu­(I) undergoes oxidative addition followed by reductive elimination to form a cross-coupled product. High stereoselectivity was found for the intramolecular C–N coupling reaction to give tetrahydroquinoxalines with an enantiomeric excess (ee) of more than 99%. For a broader application, Cu-1D was applied as the catalyst for the synthesis of a library of aziridines that gives yields of up to 99% with more than 93% recyclability for each cycle.

Stereospecific Single-Pot Route to Chiral Imidazolidines from Aziridines Using a 2D Cu Metal–Organic Framework

“…The PXRD data further confirm that the crystalline integrity of the catalyst remains intact even after four consecutive one-pot cycles (Figure S7a). A slight decrease in the yield in consecutive one-pot cycles may be due to the deactivation of active catalytic sites, as known earlier in the case of other MOFs. , However, the particle size of the catalyst was found to be reduced, as indicated by a comparative broadening of PXRD peaks after the fourth cycle (Figure S7). Stereospecificity is a decisive factor in determining how a drug interacts with the various biological molecules (enzymes, receptors, etc. )…”

“…Metal–organic frameworks (MOFs) are an important class of coordination polymers composed of organic linkers and metal ions forming an extended network of well-arranged metal nodes with permanent porosity. − The robust crystalline framework, presence of a microenvironment, and cocatalytic sites alongside an array of arranged metal centers make MOFs a steadfast cost-effective heterogeneous catalyst for various important catalytic transformations. − In this context, the design of an MOF-based catalytic system could pave an alternative heterogeneous approach toward the accessibility of biologically important imidazolidine motifs. Our previous studies include one-pot synthesis of β-arylsulfonamide and the C–N coupling reaction catalyzed using copper MOFs HKUST-1 and Cu-1D, respectively, wherein the clarity in the role of unsaturated Lewis acid sites was established. , We herein report the synthesis of a novel two-dimensional (2D) MOF with pre-existing coordinatively unsaturated sites (CUS) as an efficient ready-to-use heterogeneous catalyst for the synthesis of imidazolidine through aziridine bond cleavage in a single-pot using a nonchlorinated solvent system.…”

“…Our previous studies include one-pot synthesis of β-arylsulfonamide and the C−N coupling reaction catalyzed using copper MOFs HKUST-1 and Cu-1D, respectively, wherein the clarity in the role of unsaturated Lewis acid sites was established. 30,31 We herein report the synthesis of a novel two-dimensional (2D) MOF with pre-existing coordinatively unsaturated sites (CUS) as an efficient ready-to-use heterogeneous catalyst for the synthesis of imidazolidine through aziridine bond cleavage in a single-pot using a nonchlorinated solvent system.…”

Rationally Designed Manganese-Based Metal–Organic Frameworks as Altruistic Metal Oxide Precursors for Noble Metal-Free Oxygen Reduction Reaction

“…One of the strategies to control the morphology of mesoporous α-Mn 2 O 3 is the use of a metal–organic framework (MOF) as the template. , MOF is a porous coordinating polymer where inorganic metal nodes and organic linkers are arranged in a repeating fashion. − The ordered framework, high crystallinity, and high surface area of MOFs have been enormously applied toward catalysis, , drug delivery, sensing, gas storage, separation, and so on. Further, the calcination of a MOF is known to form metal oxide/carbon composites, with the morphology influenced by the structure of the parent MOF .…”

Thermally activated bipyridyl-based Mn-MOFs with Lewis acid–base bifunctional sites for highly efficient catalytic cycloaddition of CO2 with epoxides and Knoevenagel condensation reactions

“…These characteristics have shown their immense potential for applications in a great number of fields such as gas separation and storage, heterogeneous catalysis, fluorescence sensing, proton conduction and so on. [25][26][27][28][29][30][31][32][33][34] In particular, MOFs have inherent advantages in catalysis because they possess multiple † Electronic supplementary information (ESI) available: Tables S1-S3 and active sites including Lewis/Brønsted acid sites and Lewis base sites, which can make the use of MOFs feasible for the catalytic process. 23,[35][36][37] Moreover, the heterogeneous nature of MOFs increases the possibility of MOF catalysts for recycling and recovery.…”