Dialkyl imidazolium acetate ionosilica as efficient and recyclable organocatalyst for cyanosilylation reactions of ketones

We report new heterogeneous organocatalyst based on silica hybrid supported N-heterocyclic carbene(NHC-)species.The organocatalyst is formed from an imidazolium iodide based ionosilica material,followed by iodide/acetate anion exchange.The imidazolium acetate generates the organocatalytic carbene via partial deprotonation of the imidazolium ring in situ.As monitored via EDX,solid state NMR and ion chromatography measurements,the iodide/acetate exchange involving the imidazolium ionosilica material took place only in small extent.Despite the fact that the exchanged material contains only a very small amount of acetate,we observed good catalytic activity and recyclability in cyanosilylation reactions of ketones with trimethylsilyl cyanide.The versatility of the catalyst was highlighted via reaction with several substrates,yielding the corresponding cyanohydrins in good yields.In recycling experiments,the material showed decreasing catalytic activity starting from the third reaction cycle,but high catalytic activity can be regenerated via another acetate treatment.Our work is important as it highlights the possibility to combine carbene chemistry and silica,which are antagonistic at a first glance.We show that imidazolium acetate based ionosilicas are therefore heterogeneous'proto-carbenes',and that there is no need to form strongly basic silica supported NHCs to obtain heterogeneous NHC-organocatalysts.This work therefore opens the route towards heterogeneous and re-usable NHC-organocatalysts from supported ionic liquid imidazolium acetates.

Perfectly Green Organocatalysis： Quaternary Ammonium Base Triggered Cyanosilylation of Aldehydes

Quaternary ammonium bases, such as aqueous （CH3）4NOH, were found to be an extraordinarily efficient cata-lyst for cyanosilylation of aldehydes. The addition reaction of trimethylsilyl cyanide （TMSCN） to equivalent alde-hydes could proceed smoothly with turnover frequency （TOF） up to 3000000 h l and in near 100% yield under solvent-free conditions. These organic catalysts also tolerated various aldehydes including aromatic, aliphatic and a,fl-unsaturated aldehydes. This process perfectly conforms to the features of green chemistry： no waste regarding side-products and unconverted reactants, solvent-free, excellent catalytic activity, and no requirement for separa- tion.

Temperature-induced Sn(Ⅱ) supramolecular isomeric frameworks as promising heterogeneous catalysts for cyanosilylation of aldehydes

Two novel Sn(Ⅱ) supramolecular isomeric frameworks,with the identical formula of {(NH2Me2)2[Sn(BDC)(SO4)]}n,Sn-CP-1-α(1) and Sn-CP-1-β(2)(H2BDC=terephthalic acid) were synthesized under solvothermal condition and fully characterized by single crystal X-ray diffraction(SCXRD),Fourier transform infrared spectroscopy(FTIR),ultraviolet-visible spectroscopy(UVVis),elemental analyses,and thermogravimetric analysis(TGA).Interestingly,the structures of 1 and 2 are governed by the temperature of the reaction,suggesting a temperature-induced supramolecular isomerism.The supramolecular isomers are primarily caused by the different bridging alignments of SO42–.Compounds 1 and 2 display 2 D layer and 3 D framework with different topologies,non-interpenetrated 44-sql and two-fold interpenetrated 4-connected dia topology,respectively.Due to Lewis acid properties of coordinatively unsaturated Sn(Ⅱ) sites in CPs,they have been utilized as heterogeneous catalyst for the cyanosilylation of aldehydes with an excellent conversion yield over 99% under solvent-free conditions.

Constructing Tertiary Alcohols with Vicinal Stereocenters:Highly Diastereo-and Enantioselective Cyanosilylation of α-Branched Acyclic Ketones and Their Kinetic Resolution

We report the first highly diastereo-and enantioselective C-C bond-forming reaction of racemic α-branched ketones to construct tertiary alcohols with adjacent stereocenters.Accordingly,a highly stereoselective cyanosilylation of racemic ketones is developed using our bifunctional cyanating reagent,Me_(2)(CH_(2)Cl)SiCN,giving C^(α)-tetrasubstituted silyl cyanohydrins withtwovicinal stereocenters inupto>20:1 diastereomeric ratio(dr)and 90-98% enantiomeric excess(ee)values,which can undergo various diversification reactions bymanipulating the chloromethyl group.A highly selective kinetic resolution of acyclicα-branched ketones is also developed that allows facile access to acyclic α-alkyl,allyl,and propargyl ketones with good recovery and excellent ee values.The synthetic value of this protocol is further demonstrated by the formal synthesis of the anti-obesity agent,taranabant(MK-0364).The activation of Jacobsen’s privileged catalyst(salen)AlCl by a suitable phosphorane plays a crucial role in the reaction.X-ray crystallographic analysis of single crystals of phosphorane-(salen)AlCl complexes and theoretical calculations help provide a working model.The present transformation opens a new path for the catalytic stereoselective synthesis of stereochemically complex tertiary alcohols featuring two stereocenters(adjacent or not)from racemic ketones.

Syntheses,Structures,Fluorescence and Heterogeneous Catalysis of Coordination Polymers with 4-Benzoimidazol-1-yl-methyl Benzoic Acid and 2,2′-Dipyridine

Two coordination polymers called [Ni（L）2]n（1） and [Ni（2,2？-bpy）22（H2O）]n （2）（HL = 4-benzoimidazol-1-yl-methyl benzoic acid, 2,2？-bpy = 2,2＇-dipyridine） were synthesized by solvothermal reaction simultaneously and characterized by elemental analyses, thermogravimetric analysis, X-ray powder diffraction, IR spectroscopy and single-crystal X-ray diffraction analysis. Complex 1 crystallizes in monoclinic system, space group P21/c with a = 14.673（3）, b = 10.773（2）, c = 16.566（3） ？, V = 2559.2（8） A^3, Z = 4 and F（000） = 1160. 2 also crystallizes in monoclinic system, space group C2/c with a = 15.404（3）, b = 12.652（3）, c = 6.5362（13） ？, V = 1246.2（5） A^3, Z = 4 and F（000） = 712. The bridging L ligand connects the Ni^Ⅱ cations into a 2D network in complex 1, while 2 shows a 1D structure formed through the two O atoms of SO4^（2-） ions connecting the molecule. The catalytic properties indicate that complex 1 shows good catalytic activities for the cyanosilylation of 4-chlorobenzaldehyde. In addition, fluorescence property of complex 1 which quenches the excitation intensity in solid state was investigated at room temperature.

Recent advances in polyoxometalates acid-catalyzed organic reactions

Polyoxometalates(POMs)have conducive properties such as controlled Bronsted and Lewis acidity,high thermal stability,nontoxic nature,tunable solubility,and less corrosiveness.POMs have been extensively applied in catalytic organic reactions and have an exciting prospect for industrial applications.This review summarized recent progress in the application of POMs as acid catalysts for various organic reactions including C-C bond formation,C-N bond formation,C-O bond formation,heterocyclic synthesis reactions,cyanosilylation and hydrolysis reactions.Various POMs catalysts including heteropoly acids(HPAs)and cationic functionalized HPAs with Bronsted acidity,HPAs supported on non-precious metal support with Bronsted acidity(or both Bronsted and Lewis acidity),transition metal substituted POMs with Lewis acidity were applied in above reactions.This review attempts to provide up-to-date information about POMs acid-catalyzed organic reactions and propose future prospects.