For the first time, we have used activated alumina balls (3-5 mm diameter) for amide synthesis from carboxylic acids (unactivated) and amines (unactivated) under neat reaction conditions that produce no toxic by-products and has the advantages of being low-cost, easily available, heterogeneous, reusable and environmentally benign with no troublesome/hazardous disposal of the catalyst. † Electronic supplementary information (ESI) available. See
The evolution of proteins from simpler, selfassembled peptides provides a powerful blueprint for the design of complex synthetic materials. Previously, peptide−metal frameworks using short sequences (≤3 residues) have shown great promise as proteomimetic materials that exhibit sophisticated capabilities. However, their development has been hindered due to few variable residues and restricted choice of side-chains that are compatible with metal ions. Herein, we developed a noncovalent strategy featuring π-stacking bipyridyl residues to assemble much longer peptides into crystalline frameworks that tolerate even previously incompatible acidic and basic functionalities and allow an unprecedented level of pore variations. Single-crystal X-ray structures are provided for all variants to guide and validate rational design. These materials exhibit hallmark proteomimetic behaviors such as guest-selective induced fit and assembly of multimetallic units. Significantly, we demonstrate facile optimization of the framework design to substantially increase affinity toward a complex organic molecule.
The reaction of equimolar amounts of UO 2 (OAc) 2 • 2H 2 O, 2,6-diformyl-4-methylphenol, and N-(hydroxyethyl)ethylenediamine in methanol affords a dinuclear trans-uranyl(VI) complex of the molecular formula [(UO 2 ) 2 (μ-L) 2 ] (L 2− = 2-formyl-4methyl-6-((2-(2-oxidoethylamino)ethylimino)methyl)phenolate) in 65% yield. Detailed structural elucidation of the complex was performed by using single-crystal X-ray crystallographic and spectroscopic studies. In [(UO 2 ) 2 (μ-L) 2 ], the metal centers are in edge-shared pentagonal-bipyramidal N 2 O 5 coordination spheres assembled by the two meridional ONNO-donor bridging L 2− and two pairs of mutually trans oriented oxo groups. The complex is redox active and displays two successive metal-centered one-electron reductions at E pc = −0.71 and −1.03 V in N,N-dimethylformamide solution. The redox-active complex was used as a heterogeneous catalyst for electrochemical hydrogen evolution from aqueous medium at pH 7 with a turnover frequency (TOF) of 384 h −1 and a Tafel slope of 274 mV dec −1 . The Faradaic efficiency of [(UO 2 ) 2 (μ-L) 2 ] was found to be 84%. Beyond the electrocatalytic response, the [(UO 2 ) 2 (μ-L) 2 ]-TiO 2 −N719 composite also exhibited significant heterogeneous photocatalytic hydrogen evolution activity in neutral aqueous medium under visible light and provided a yield of 3439 μmol g cat −1 of H 2 in 4 h with a TOF of 172 h −1 and apparent quantum yield (AQY) of 7.6%.
Complexes of the {(UO2)2(μ-OH)2}2+ core with N,N,O-donor 2-((2-(6-chloropyridazin-3-yl)hydrazono)methyl)-4-R-phenolates and their visible light-induced photocatalytic organic dye degradation abilities are reported.
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