Aluminum phthalocyanine: an active and simple catalyst for cyanosilylation of aldehydes

Aluminum phthalocyanine (AlPc) in the presence of Ph₃PO acts as a highly effective catalyst for cyanosilylation of various aldehydes to the corresponding cyanohydrin trimethylsilyl ethers. The reaction proceeds smoothly with 5 mol% catalyst loading at room temperature, giving up to 96% yield. Copyright © 2007 John Wiley & Sons, Ltd.     

A comparison of homogeneous and heterogeneous copper catalyzed arylation of amines

Comparison of the homogeneous and heterogeneous copper-catalyzed arylation of model primary amines with (hetero)-aryl iodides in DMSO revealed a comparable efficiency of CuI and commercially available unsupported copper nanoparticles (25 nm size) in the presence of 2-isobutyryl-cyclohexanone or L-proline.     

Synthesis and reactivity of homogeneous and heterogeneous ruthenium-based metathesis catalysts containing electron-withdrawing ligands

The synthesis and heterogenization of new Grubbs-Hoveyda type metathesis catalysts by chlorine exchange is described. Substitution of one or two chlorine ligands with trifluoroacetate and trifluoromethanesulfonate was accomplished by reaction of [RuCl(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (IMesH(2) = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) with the silver salts CF(3)COOAg and CF(3)SO(3)Ag, respectively. The resulting compounds, [Ru(CF(3)SO(3))(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (1), [RuCl(CF(3)SO(3))([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (2), and [Ru(CF(3)CO(2))(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (3) were found to be highly active catalysts for ring-closing metathesis (RCM) at elevated temperature (45 degrees C), exceeding known ruthenium-based catalysts in catalytic activity. Turn-over numbers (TONs) up to 1800 were achieved in RCM. Excellent yields were also achieved in enyne metathesis and ring-opening cross metathesis using norborn-5-ene and 7-oxanorborn-5-ene-derivatives. Even more important, 3 was found to be highly active in RCM at room temperature (20 degrees C), allowing TONs up to 1400. Heterogeneous catalysts were synthesized by immobilizing [RuCl(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] on a perfluoroglutaric acid derivatized polystyrene-divinylbenzene (PS-DVB) support (silver form). The resulting supported catalyst [RuCl(polymer-CH(2)-O- CO-CF(2)-CF(2)-CF(2)-COO)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (5) showed significantly reduced activities in RCM (TONs = 380) compared with the heterogeneous analogue of 3. The immobilized catalyst, [Ru(polymer-CH(2)-O-CO-CF(2)-CF(2)-CF(2)-COO)(CF(3)CO(2))([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (4) was obtained by substitution of both Cl ligands of the parent Grubbs-Hoveyda catalyst by addition of CF(3)COOAg to 5. Compound 4 can be prepared in high loadings (160 mg catalyst g(-1) PS-DVB) and possesses excellent activity in RCM with TONs up to 1100 in stirred-batch RCM experiments. Leaching of ruthenium into the reaction mixture was unprecedentedly low, resulting in a ruthenium content <70 ppb (ng g(-1)) in the final RCM-derived products.     

Layered double hydroxides (LDHs): As efficient heterogeneous catalyst for the cyanosilylation of aromatic aldehydes

We report the first application of Layered Double Hydroxides (LDHs) as efficient and novel heterogeneous catalyst for the cyanosilylation of aldehydes with excellent yields and simple work up. The reaction between different aldehydes with electron-withdrawing and releasing groups and trimethylsilyl cyanide (TMSCN) proceeds in dry CH₂Cl₂ at room temperature in the presence of Mg-Al-Cu LDH. The catalyst recycled and reused for four times without loss of catalytic activity. The structures of all compounds were corroborated spectroscopically (¹H- and ¹³C-NMR, and elemental analysis). A plausible mechanism for this type of reaction is proposed.     

Silsesquioxane-based homogeneous and heterogeneous epoxidation catalysts developed by using high-speed experimentation

A set of new titanium-silsesquioxane epoxidation catalysts was discovered by exploring the hydrolytic condensation of a series of trichlorosilanes in highly polar solvents by means of high-speed experimentation techniques. The most promising silsesquioxane leads were prepared on a conventional laboratory scale and fully characterised. The lead generated by the hydrolytic condensation of tBuSiCl(3) in DMSO consisted of a set of incompletely condensed silsesquioxane structures, whereas that obtained from the hydrolytic condensation of tBuSiCl(3) in water consisted of a single silsesquioxane structure, tBu(2)Si(2)O(OH)(4). This is the first reported example of the use of this silsesquioxane as a precursor for active Ti catalysts. The Ti complexes prepared with tBu(2)Si(2)O(OH)(4) were supported on silica to produce active heterogeneous epoxidation catalysts.     

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.     

Enantioselective cyanosilylation of aldehydes catalyzed by Mn(salen) complex/triphenyl phosphine oxide

The activation of chiral Mn(salen) complexes with Ph₃PO has been found to provide a good strategy for the asymmetric cyanosilylation of aldehydes. Aromatic aldehydes have been converted into the corresponding cyanohydrin trimethylsilylether in yields up to 95% and ee up to 67% using 0.25 mol% chiral Mn(salen) complex in combination with 10 mol% of achiral Ph₃PO as additive. Copyright © 2007 John Wiley & Sons, Ltd.     

Gold-catalyzed synthesis of chroman, dihydrobenzofuran, dihydroindole, and tetrahydroquinoline derivatives

Different furans containing an ynamide or alkynyl ether moiety in the side chain were prepared. The gold-catalyzed transformation of these compounds delivered dihydroindole, dihydrobenzofuran, chroman, and tetrahydroquinoline derivatives at room temperature through very fast reactions. Furthermore, the stabilizing effect of the heteroatom directly attached to the intermediate arene oxides led to highly selective reactions, even in the case of only mono-substituted furans, which is quite different from previous results obtained with non-heteroatom-substituted alkynes.     

Gold‐Catalyzed Reactions of 1,5‐ and 1,6‐Enynes with Carbonyl Compounds: Cycloaddition vs. Metathesis

Gold and rings : The gold(I)‐catalyzed addition of aldehydes to 1,6‐enynes gives 1,3‐dienes, by a cycloaddition/fragmentation process. 1,5‐Enynes react with aldehydes and ketones by the 5‐endo‐dig pathway to give the corresponding cycloadducts.

     

Germylene Cyanide Complex: A Reagent for the Activation of Aldehydes with Catalytic Significance

The first example of a germanium(II) cyanide complex [GeCN(L)] ( 2 ) (L=aminotroponiminate (ATI)) has been synthesized through a novel and relatively benign route that involves the reaction of a digermylene oxide [(L)Ge?O?Ge(L)] ( 1 ) with trimethylsilylcyanide (TMSCN). Interestingly, compound 2 activates several aldehydes (RCHO) at room temperature and results in the corresponding cyanogermylated products [RC{OGe(L)}(CN)H] (R=H 3 , iPr 4 , tBu 5 , CH(Ph)Me 6 ). Reaction of one of the cyanogermylated products ( 4 ) with TMSCN affords the cyanosilylated product [(iPr)C(OSiMe₃)(CN)H] ( 7 ) along with [GeCN(L)] quantitatively, and insinuates the possible utility of [GeCN(L)] as a catalyst for the cyanosilylation reactions of aldehydes with TMSCN. Accordingly, the quantitative formation of several cyanosilylated products [RC(OSiMe₃)(CN)H] ( 7 – 9 ) in the reaction between RCHO and TMSCN by using 1 mol % of [GeCN(L)] as a catalyst is also reported for the first time.     

Gold‐Catalyzed Intermolecular Addition of Carbonyl Compounds to 1,6‐Enynes: Reactivity,Scope, and Mechanistic Aspects

A full account of a recently discovered gold(I)‐catalyzed reaction, a cycloaddition of carbonyl compounds to enynes yielding 2‐oxabicyclo[3.1.0]hexanes with four stereogenic centers, is presented. The reaction proceeds with very high diastereoselectivity. The scope of the reaction has been investigated. In addition, experiments and DFT calculations concerning mechanistic aspects were carried out. The reaction course varies with the substitution pattern of the alkene moiety of the starting enyne. Branched olefins led to 2‐oxabicyclo[3.1.0]hexanes; terminally substituted olefins proceeded with the incorporation of two carbonyl components to give hexahydrocyclopenta[d][1,3]dioxines.