Gold-like Thiolate-Protected Ultrasmall Cubic Copper Nanocluster-Based Metal–Organic Framework as a Selective Catalyst for Stepwise Synthesis of Unsymmetric Bistriazole by Click Reaction

Abstract

We report a facile synthesis of a thiolate-protected water-soluble ultrasmall cubic copper nanocluster-based metal–organic framework (CuMOF) as an efficient and chemoselective catalyst for the azide–alkyne click reaction. Interestingly, the diffuse reflectance spectra of CuMOFs exhibit three discrete plasmon bands at 463, 505, and 674 nm, which are similar to those corresponding to the fingerprint region of thiolate-protected atomically precise Au25 nanoclusters; hence, CuMOFs are termed as gold-like ultrasmall cubic copper nanoclusters. The high-resolution transmission electron microscopy (HRTEM) and powder X-ray diffraction (XRD) patterns confirm the cubic morphology of CuMOFs with nanoclusters showing particle size distribution of ∼2–12 nm. The matrix-assisted laser desorption ionization (MALDI) spectrum of CuMOFs is attributed to the individual particles consisting of few Cu n (SR) m with Cu(0) core atoms and Cu­(I)­SR staples, i.e., Cu2(SR)4, Cu­(SR)6, Cu3(SR)7, and Cu4(SR)8. To our surprise, the unsymmetric bistriazoles resulting from the click reaction of bifunctional azides and alkynes in the presence of CuMOFs were achieved by step-by-step conversion of the terminal azide selectively with maximum yield in the range of 70–88%. The nitrogen adsorption–desorption studies confirm the size-dependent surface area, pore volume, and pore size for the CuMOFs prepared by varying metal-to-ligand ratios. The plausible mechanism for the selective mono-click at CuMOFs suggests the existence of bifunctional terminal interactions via thiol and sulfonate groups that might have provided the site-isolation-based active sites for selective catalysis. The easy recovery of CuMOFs and their reusability up to 5 times without significant loss of activity are very promising for the selective organic conversions in pharmaceutical and industrial formulations.

General Method to Synthesize Highly Stable Nanoclusters via Pickering-Stabilized Microemulsions

“…A suitable reducing agent, e.g., NaBH 4 for Au 3+ , is used to trigger a fast reduction during which very small metallic Au species form. To prevent the newly formed Au from growing into larger particles, mercaptoethanol is used to passivate the particle growth due to the strong Au–S bond . As discussed in detail further below, metallic Au is first formed inside the water droplets and then attaches to the W/O interface (S2).…”

“…To prevent the newly formed Au from growing into larger particles, mercaptoethanol is used to passivate the particle growth due to the strong Au–S bond. 26 As discussed in detail further below, metallic Au is first formed inside the water droplets and then attaches to the W/O interface (S2). The resulting enrichment of the micellar interface with Au nanoclusters results in a Pickering stabilization effect and changes the properties of the emulsion interface, resulting in an outbound diffusion of water during the following hydrolysis upon the slow addition of tetraethyl orthosilicate (TEOS) to the reaction system (S2).…”

Advanced Functionalized Nanoclusters (Cu, Ag, and Au) as Effective Catalyst for Organic Transformation Reactions

“…[124] For the purpose of selective click chemistry azide-alkyne reactions, R. Murugan and colleagues revealed a novel and simple method for synthesising gold-like, thiolate-protected ultra-small cubic Cu-MOFs (2) (MOF = metal organic framework). [125] The Cu(NO 3 ) 2 and 3-mercaptopropyl sulfonate, a stabilizer, were mixed in 150 mL of distilled water for the production of 2 NC. To keep the temperature below room temperature, the solution of dissolved components was kept in contact with ice.…”

Magnetic Cu/Co nanoparticles supported on nitrogen‐doped porous carbon derived from Cu/Co@aZIF: Investigation of catalytic activity and structural properties

“…The advantages of the AAC catalytic system catalyzed by Cu/Co@NPC over other MOF-derived catalysts are as follows: (1) requires less catalyst concentration; (2) shorter reaction time; (3) high efficiency with chlorinated substrates; and (4) high reusability. To the best of our knowledge, the Cu/Co@NPC is the only catalyst that combines Cu-MOF 5 mol%, 0.37 mmol, EtOH/H 2 O, rt, 12 h 95 [45] Cu25%/ZIF-8 5 mol% catalyst, 1 mmol, EtOH, 70 C, 3 h 99 [46] Cu(I)-MOF 1 mol% (based on Cu element), 1 mmol, DMF/DMSO, 60 C, 4 h 99 [47] CuI@UiO-67-IM 2 mol%, 1 mmol, H 2 O, 80 C, 2 h 89 [48] Cu-MOF 0.25 mol%, 1 mmol, neat, 50 C, 2.5 h 94 [49] Copper-MOF 0.1 mol%, 1 mmol, EtOH, 70 C, 1 h 99 [50] Cu-MOF 10 mol%, 1 mmol, H 2 O/MeOH, 70 C, 2 h, sodium ascorbate, K 2 CO 3 93 [51] Cu(BTC)-MOF 10 mg, 1.6 mmol, MeOH, rt, 16 h 88 [52] Cu(INA) 2 -MOF 1 mol%, 0.5 mmol, solvent free, 80 C, 4 min 95 [53] MOF-2 1 mol%, 0.1 mmol, H 2 O/CH 3 CN, rt (WLED [24 W]), 8 h 45 [54] Abbreviations: MOF, metal-organic framework; WLED, white light-emitting diode; NPC, Nitrogen-doped porous carbon; DMF, Dimethylformamid; ZIF, Zeolitic imidazolate framework; BTC, benzene-1,3,5-tricarboxylic acid; INA, isonicotinate ion.…”