Preparation of Anisotropic MnO2 Nanocatalysts for Selective Oxidation of Benzyl Alcohol and 5-Hydroxymethylfurfural

Anisotropic MnO2 nanostructures,includingα-phase nanowire,α-phase nanorod,δ-phase nanosheet,α+δ-phase nanowire,and amorphous fl occule,were synthesized by a simple hydrothermal method through adjusting the pH of the precursor solution and using diff erent counterions.The catalytic properties of the as-synthesized MnO2 nanomaterials in the selective oxidation of benzyl alcohol(BA)and 5-hydroxymethylfurfural(HMF)were evaluated.The eff ects of micromorphology,phase structure,and redox state on the catalytic activity of MnO2 nanomaterials were investigated.The results showed that the intrinsic catalytic oxidation activity was mainly infl uenced by the unique anisotropic structure and surface chemical property of MnO2.With one-dimensional and 2D structures exposing highly active surfaces,unique crystal forms,and high oxidation state of Mn,the intrinsic activities for MnO2 catalysts synthesized in pH 1,5,and 10 solutions(denoted as MnO2-pH1,MnO2-pH5,and MnO2-pH10,respectively)were twice higher than those of other MnO2 catalysts in oxidation of BA and HMF.With a moderate aspect ratio,theα+δnanowire of MnO2-pH10 exhibited the highest average oxidation state,most abundant active sites,and the best catalytic oxidation activity.

Synthesis of Mono-fluoroallenes through Copper-Catalyzed Defluorinative Silylation of α,α-Difluoroalkylalkynes

A straightforward protocol for the synthesis of mono-fluorinated allenes via catalytic defluorinative silylation of the readily availableα,α-difluoroalkylalkynes with commercially available copper catalyst and phosphine ligand is described.A broad scope ofα,α-difluoroalkylalkynes were well accommodated and a gram-scale synthesis demonstrated the synthetic utility of this methodoglogy.

Oxidation of Difluorocarbene by Pyridine N-Oxide and Ensuing Access to Carbamoyl Fluorides

A practical one-pot preparation of carbamoyl fluorides from easily obtained pyridine N-oxide,commercially available secondary amines and synthetically versatile difluorocarbene precursors(Ruppert-Prakash reagent or Chen's reagent)was developed herein,which dexterously resorted to the oxidation of difluorocarbene by external pyridine N-oxide to produce the toxic and gaseous fluorophosgene in situ.Notable features of this method include nice functionality tolerance,late-stage modification of drug molecules and the recoveryand recycle of quinoline.

Boring holes in Au nanoplates by active surface etching

In contrast to the conventional etching that makes nanoparticles rounder and our previous sharpening etching mode that causes serrated edges,here,we developed a new boring etching mode that targets the faces of Au nanoplates to make holes.The critical factors are the pre-incubation step with the ligand 2-mercapto-5-benzimidazolecarboxylic acid(MBIA)and the subsequent removal of excess ligands in the solution.Thus,etching is focused onto the few sites with initial loss of ligands,which cannot be quickly replaced.The choice of ligand MBIA is also of importance,as it carries negative charge and repels each other.Its inability of forming a dense layer probably plays a critical role in the site-selectivity for faces,because ligands at the higher curvature edges and corners are expected to have less repulsion.The etching results from the comproportionation reaction between Au3+and Au0 in the nanoplates,where Br-coordination to Au and the extra stabilization from cetyltrimethylammonium bromide(CTAB)are essential.We believe that the ability of boring holes is an important tool for future synthetic designs.

Expedient Trifluoromethylacylation of Styrenes Enabled by Photoredox Catalysis

Herein,we disclosed a photoredox enabled protocol for trifluoromethylacylation of styrenes through a radical-carboanion cascade and subsequent oxidation.With a broad range of aldehydes and inexpensive Langlois reagent as acyl and CF3 precursor,respectively,the alkene motif could be readily converted into β-trifluoromethyl ketones in moderate to good yields and with excellent regioselectivity.Besides CF3,di-,mono-and non-fluorinated C-radicals were revealed amenable in this reaction,providing good opportunity for the construction of structurally diverse ketones of interest in pharmaceutical research.Additionally,the utility of this protocol was further demonstrated by successful extension to trifluoromethylarylation and-alkylation by employing arylcyanide or acrylates in place of carbonyls.

Monitoring the rapid nanocrystal transformation via trapped intermediates of silica encapsulation

In transmission electron microscopy(TEM),encapsulation is an important tool to preserve the nanoparticles from aggregation,weathering,and destructive highenergy electron beam.Traditionally,encapsulation can only be used to trap end products.This study pushes the limit of in situ encapsulation so that intermediates of short time scale can be trapped.Nanocrystals of water-soluble salts were generated from a solute-induced phase separation(SIPS)process.By performing a modified Stober encapsulation on different time points of the process,a series of intermediates can be trapped by silica shells.By arranging and comparing the intermediates,it is possible to reconstruct the growing process of those water-soluble salt nanocrystals.Moreover,an example of the transition from nanocrystal to liquid droplet was discovered,unveiling a potentially alternative route of the SIPS process.The reported technique could capture more snapshots for TEM imaging,providing crucial information on the study of nanoscale growth mechanism.

The patchy growth mode:Modulation of the Au-Au interface via phenynyl ligands

Surface ligands play critical roles in nanosynthesis and thus it is of great importance in expanding the scope of suitable ligands.In this work,we explore phenynyl ligands in modulating the Au-Au interface when growing Au domains on Au seeds.A patchy growth mode is observed where the emerging islands are flat-laying with holes and branches.This growth mode is distinctively different from the conventional facet-controlled growth using weak ligands,and the non-wetting island growth using strong ligands.Through manipulating the molecular structure and the packing of the phenynyl ligands on the Au seeds,the overgrown Au domains are continuously tuned,from patches to islands,extending the plasmon absorption peak into the near-infrared spectral range.We believe that the new ligand with intermediate affinity and the unusual growth mode would expand the control in both synthesis and application.

Turning weak into strong: on the CTAB-induced active surface growth

Discovering new methods and principles in the inequivalent growth of equivalent facets is of great significance for going beyond symmetrical nanocrystals and for out-of-box exploration. In this work, we demonstrate that a middle ground exists between the traditional weak ligands and the strong ligands with unusual growth modes. By modifying the seed concentration during the growth of pentagonal Au nanorods, the typical weak ligand cetyltrimethylammonium bromide(CTAB) is made strong, leading to notches of restricted growth and even the active surface growth mode. In-depth investigation in the link between growth kinetics and ligand packing reveals the principle of their interplay —— that the on-off dynamics of the ligands only allows for a certain limit of materials deposition rate. Beyond this limit, the growth materials build up and are then diverted elsewhere, leading to inequivalent growth. The fact that a freshly grown surface has few ligands promotes the active surface growth, focusing the growth materials onto a few sites. We believe that the knowhow of interfering ligand packing via growth kinetics would offer a powerful tool of synthetic control, where the facet-and curvature-dependent ligand packing is expected to be useful synthetic handles.