Showing papers on "Heck reaction published in 2013"

Enantioselective redox-relay oxidative heck arylations of acyclic alkenyl alcohols using boronic acids.

Abstract: A general, highly selective asymmetric redox-relay oxidative Heck reaction using achiral or racemic acyclic alkenols and boronic acid derivatives is reported. This reaction delivers remotely functionalized arylated carbonyl products from acyclic alkenol substrates, with excellent enantioselectivity under mild conditions, bearing a range of useful functionality. A preliminary mechanistic investigation suggests that the regioselectivity of the initial migratory insertion is highly dependent on the electronic nature of the boronic acid and more subtle electronic effects of the alkenyl alcohol.

Palladium-catalyzed coupling reactions : practical aspects and future developments

Abstract: PREFACE PALLADIUM-CATALYZED CROSS-COUPLING REACTIONS - A GENERAL INTRODUCTION Introduction Carbon - Carbon Cross-Coupling Reactions Catalyzed by Palladium The Catalysts Mechanistic Aspects Future Challenges HIGH-TURNOVER HETEROGENEOUS PALLADIUM CATALYSTS IN COUPLING REACTIONS: THE CASE OF PD LOADED ON DEALUMINATED Y ZEOLITES Introduction Various Methodologies to Afford High Turnover Numbers Over Supported Pd Catalysts Structure and Characteristics of Ultrastable Y Zeolites Suzuki - Miyaura Reactions Catalyzed by Pd/USY Catalytic Performance of Pd/USY in Mizoroki - Heck Reactions Conclusion and Perspective PALLADIUM-CATALYZED COUPLING REACTIONS WITH MAGNETICALLY SEPARABLE NANOCATALYSTS Introduction General Considerations Concerning Magnetic Particles as Catalyst Supports Palladium Nanoparticles on Magnetic Supports Molecular Palladium Complexes on Magnetic Supports Outlook THE USE OF ORDERED POROUS SOLIDS AS SUPPORT MATERIALS IN PALLADIUM-CATALYZED CROSS-COUPLING REACTIONS Introduction Catalyst Synthesis and Characterization Carbon - Carbon Couplings Miscellaneous Coupling Reactions The Question of Solution-Phase Catalysis Summary and Future Prospects COUPLING REACTIONS INDUCED BY POLYMER-SUPPORTED CATALYSTS Introduction Polysaccharides Poly(ethylene glycol) Polystyrene Poly(norbornene) Polyacrylamide Polyaniline Poly(N-vinyl-2-pyrrolidone) Polypyrrole Poly(4-vinylpyridine) Ionic Polymers Organometallic Polymers Functionalized Porous Organic Polymers Miscellaneous Polymers Summary and Outlook COUPLING REACTIONS IN IONIC LIQUIDS Introduction Metal Complexes Metal Salts and Metal on Solid Support Metal Nanoparticles Summary and Outlook CROSS-COUPLING REACTIONS IN AQUEOUS MEDIA Introduction Cross-Coupling of Organic Halides to Form C--C Bonds in Aqueous Media Carbon - Heteroatom Coupling Reactions C--H Activation in Aqueous Media Conclusion and Future Prospects MICROWAVE-ASSISTED SYNTHESIS IN C--C AND CARBON - HETEROATOM COUPLING REACTIONS Introduction C--C Bond Formation C--X Bond Formation Conclusions CATALYST RECYCLING IN PALLADIUM-CATALYZED CARBON - CARBON COUPLING REACTIONS Introduction General Issues of Catalyst Recycling Catalyst Systems Providing High, Consistent Yields in Recycling Catalysts Affording the Highest Cumulative TON Values in Recycling Studies Summary Evaluation Future Outlook NATURE OF THE TRUE CATALYTIC SPECIES IN CARBON - CARBON COUPLING REACTIONS WITH HETEROGENEOUS PALLADIUM PRECATALYSTS Introduction Heck Reactions Suzuki Reactions Sonogashira Reactions Concluding Remarks COUPLING REACTIONS IN CONTINUOUS-FLOW SYSTEMS Introduction Coupling Reactions in Flow Palladium Catalysts for Flow Systems Continuous-Flow Technologies for Cross-Coupling Summary and Outlook PALLADIUM-CATALYZED CROSS-COUPLING REACTIONS - INDUSTRIAL APPLICATIONS Introduction Suzuki - Miyaura Reactions Heck - Mizoroki Reactions Sonogashira - Hagihara Reactions Carbonylations Cyanations Negishi Coupling Novel Pd-Catalyzed C--C Cross-Coupling Reaction Buchwald - Hartwig Aminations Pd-Catalyzed C--S Bond Formation Summary and Outlook

Redox of ferrocene controlled asymmetric dehydrogenative Heck reaction via palladium-catalyzed dual C–H bond activation

Abstract: A novel strategy of dehydrogenative Heck reaction controlled by redox process of ferrocene has been developed. Commercially available chiral amino acid as ligand realized asymmetric dehydrogenative Heck reaction, leading to planar-chiral ferrocene derivatives with excellent enantioselectivity and in good to excellent yields (up to 99% ee and 98% yield).

Palladium Nanoparticles Immobilized on Nano-Silica Triazine Dendritic Polymer (Pdnp-nSTDP): An Efficient and Reusable Catalyst for Suzuki–Miyaura Cross-Coupling and Heck Reactions

Abstract: A new catalyst based on palladium nanoparticles immobilized on nano-silica triazine dendritic polymer (Pdnp-nSTDP) was synthesized and characterized by FT-IR spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy dispersive X-ray, transmission electron microscopy and elemental analysis. The size of the palladium nanoparticles was determined to be 3.1±0.5 nm. This catalytic system showed high activity in the Suzuki–Miyaura cross-coupling of aryl iodides, bromides and chlorides with arylboronic acids and also in the Heck reaction of these aryl halides with styrenes. These reactions were best performed in a dimethylformamide (DMF)/water mixture (1:3) in the presence of only 0.006 mol% and 0.01 mol% of the catalyst, respectively, under conventional conditions and microwave irradiation to afford the desired coupling products in high yields. The Pdnp-nSTDP was also used as an efficient catalyst for the preparation of a series of star- and banana-shaped compounds with a benzene, pyridine, pyrimidine or 1,3,5-triazine unit as the central core. Moreover, the catalyst could be recovered easily and reused several times without any considerable loss of its catalytic activity.

Aerobic oxidative Heck/dehydrogenation reactions of cyclohexenones: efficient access to meta-substituted phenols.

Abstract: Phenol derivatives are common and important structural motifs in bioactive natural products and pharmaceuticals,[1] and the selective synthesis of substituted phenols is facilated by the strong ortho/para-directing effect of the hydroxyl group. The same directing effect, however, limits access to analogous meta-substituted derivatives. In recent years, considerable efforts have targeted C–H functionalization reactions that enable preparation of meta-substituted arenes via steric[2] or directing-group[3] control over the site selectivity. The overall efficiency of these methods is often limited by functional group interconversions or installation/removal of directing groups needed to access the final product.[4] Moreover, in molecules with more than one electronically or sterically active substituent, competition between the directing groups can lead to product mixtures. Following our recent development of Pd-catalyzed aerobic dehydrogenation reactions of ketones,[5,6,7] we envisioned that meta-substituted phenols could be accessed efficiently via an aerobic oxidative Heck/dehydrogenation sequence with cyclohexenone (Scheme 1).[8] Cyclohexenone is a convenient and inexpensive phenol precursor, and the proposed strategy exploits the intrinsic regioselectivity of additions to electron-deficient alkenes to enable functionalization of the "meta" C–H bond. Here, we describe a new Pd catalyst and reaction conditions compatible with this sequence, and we showcase their utility in the synthesis of a pharmaceutically active phenol derivative. Scheme 1 Strategy for the synthesis of meta-substituted phenols. The proposed sequence in Scheme 1 faces several challenges. The oxidative Heck reaction must be more facile than the dehydrogenation step in order to avoid direct conversion of the cyclohexenone starting material to unsubstituted phenol. Furthermore, while aerobic oxidative Heck reactions have extensive precedent with terminal alkenes,[9, 10] analogous reactions with cyclohexenone tend to be more difficult.[11,12] With this substrate, the PdII-enolate must isomerize to place the Pd atom on the opposite side of the ring in order to undergo β-hydride elimination (Scheme 2.[13] Finally, the catalyst and conditions must be compatible with both reactions in the sequence. The only general method for dehydrogenation of cyclohexenones to phenols employs a strong-acid additive (p-TsOH; Scheme 3),[5a] which interferes with oxidative Heck reactions.[14] Scheme 2 Mechanistic steps highlighting the requirement for isomerization of the PdII-enolate intermediate in Heck reactions of cyclohexenone. Scheme 3 Previously reported aerobic dehydrogenation conditions for the synthesis of phenols. Our initial studies targeted the identification of non-acidic reaction conditions for aerobic dehydrogenation of 3-methylcyclohexenone. Upon screening diverse PdX2 sources, ligands, additives and solvents (see Supp. Info. for full screening data), we found that the dicationic PdII complex [Pd(CH3CN)4](BF4)2 was particularly effective as a catalyst (Table 1). Formation of Pd black and gradual loss of catalytic activity during the reaction prompted us to test ancillary ligands to stabilize the catalyst. Most of the ligands tested inhibited the reaction (cf. Table 1 and Supp. Info.); however, 4,5-diazafluorenone L4[15] and 6,6'-dimethyl-2,2'-bipyridine L5 enabled good product yields to be obtained. While screening of numerous additives, including Bronsted bases, CuII and AgI salts, and quinones showed little beneficial effect, nearly quantitative yield of the phenol product (95%) was obtained when 9 mol % AMS (anthraquinone-2-sulfonic acid sodium salt) was included in the reaction with ligand L5.[16] The optimal result was obtained upon addition of water (20 vol %) to enhance the solubility of AMS. Table 1 Dehydrogenation of 3-Cyclohexenones: Screening Results.[a] The optimized conditions proved to be effective with a number other substituted cyclohexenones, including those with heteroatom substituents (Table 2). These neutral reaction conditions revealed some advantages over the previously reported conditions in Scheme 3. For example, 6-phenylcyclohexanone underwent dehydrogenation to o-phenyl phenol in only 33% yield under the previous conditions, but this product is obtained in excellent yields under the present conditions (entries 1 and 2). The successful reaction of 3-arylcyclohexenones, prepared via oxidative Heck reactions with cyclohexenone (entries 9–11), provided a useful starting point for the investigation of oxidative Heck and tandem oxidative Heck/dehydrogenation reactions. Table 2 Dehydrogenation of Substituted Cyclohexenones,[a] Preliminary experiments showed that this catalyst was quite effective for the oxidative Heck coupling of 4-methoxyphenylboronic acid and cyclohexenone. Moveover, the reaction could take place at 50 °C, a temperature at which no conversion of cyclohexenone to phenol was observed. In DMSO, the oxidative Heck reaction proceeded in 65% yield. Upon heating of this reaction mixture to 80 °C, nearly complete in situ conversion to the 3-aryl phenol was observed (i.e., 64% yield of the phenol; Table 3, entry 1). Several other solvents, including DMF, N-methylpyrrolidone (NMP) and 1,4-dioxane, proved to be better for the oxidative Heck reaction (entries 2–7); however, they proved less effective for the tandem sequence (e.g., entry 2). Further studies revealed that an effective one-pot sequence could be achieved by performing the oxidative Heck reaction in NMP at 50 °C, followed by addition of DMSO and heating to 80 °C for the dehydrogenation step. This protocol enabled a good yield of the phenol to be obtained (84%, entry 12). Table 3 Optimization of Conditions for the Oxidative Heck and one-pot Oxidative Heck/Dehydrogenation Reactions.[a] [Pd(CH3CN)4](BF4)2/L5 proved to be very effective as a standalone catalyst for oxidative Heck reactions with cyclohexenone. Good yields of the 3-arylcyclohexenones were obtained with diverse arylboronic acids (Table 4). Reactions with the electron-rich arylboronic acids typically led to higher yields than electron-deficient substrates as the latter substrates were more susceptible to the formation of homocoupling products. Halogenated arylboronic acids (X = F, Cl, Br) were tolerated in the oxidative Heck reaction, with yields ranging from 68% to 86% (entries 4–6 and 18). The same arylboronic acids were then employed in the one-pot oxidative Heck/dehydrogenation to afford the 3-substituted phenol derivatives. In most cases, the phenol yields correlate closely with the yields of the 3-aryl cyclohexenones in the independent oxidative Heck reaction. Table 4 Oxidative Heck and One-Pot Oxidative Heck/Dehydrogenation Reactions to Prepare Substituted Cyclohexenones and Phenols.[a] In order to demonstrate the potential utility of the aerobic oxidative Heck/dehydrogenation sequence and further test its functional group compatibility, we investigated the synthesis of URB597 from cyclohexenone and the commercially available benzamide-derived boronic acid 1 (Scheme 4). URB597 is a potent inhibitor of fatty acid amide hydrolase (FAAH) and an important focus of efforts to treat pain, anxiety and depression.[17,18] The phenol intermediate 3 was prepared via stepwise oxidative Heck coupling of 1 and cyclohexenone, followed by catalytic dehydrogenation of the isolated intermediate 2, and in a direct, one-pot process. The [Pd(CH3CN)4](BF4)2/L5 catalyst was employed for each of these steps, and both pathways led to the phenol product 3 in good yield (approx. 72%, in each case). Scheme 4 Application of one-pot oxidative Heck/dehydrogenation reactions in the synthesis of URB597. The results above highlight a new catalyst system that mediates both aerobic oxidative Heck reactions with cyclohexenone and aerobic dehydrogenation of cyclohexenones. The one-pot sequence developed for these reactions represents an efficient strategy for the preparation of meta substituted of phenols, which should be advantageous or highly competitive with other approaches based on C–H functionalization of an aromatic ring.

Palladium-Catalyzed Difunctionalization of Enol Ethers to Amino Acetals with Aminals and Alcohols

Abstract: A new strategy was developed for intercepting the palladium–alkyl species generated in Heck reaction via nucleophilic addition prior to the step of migratory insertion, which leads to a new palladium-catalyzed difunctionalization of enol ethers with aminals and alcohols to afford amino acetals. Mechanistic studies suggested that the cationic cyclometalated Pd(II) complex generated by the oxidative addition of aminal to a Pd(0) species was crucial for this unusual transformation.

Mechanistic study of the oxidative coupling of styrene with 2-phenylpyridine derivatives catalyzed by cationic rhodium(III) via C-H activation.

Abstract: The Rh(III)-catalyzed oxidative coupling of alkenes with arenes provides a greener alternative to the classical Heck reaction for the synthesis of arene-functionalized alkenes. The present mechanistic study gives insights for the rational development of this key transformation. The catalyst resting states and the rate law of the reaction have been identified. The reaction rate is solely dependent on the catalyst and alkene concentrations, and the turnover-limiting step is the migratory insertion of the alkene into a Rh–C(aryl) bond.

Palladium nano-particles supported on ethylenediamine-functionalized cellulose as a novel and efficient catalyst for the Heck and Sonogashira couplings in water

Abstract: Palladium nano-particles supported on ethylenediamine-functionalized cellulose as a novel bio-supported catalyst were synthesized and characterized. The synthesized catalyst was found to be a highly efficient heterogeneous catalyst for the Heck and Sonogashira couplings in H2O as a green solvent at 100 °C in very low loading of Pd. The catalyst could be easily recovered by simple filtration and reused for at least 4 cycles without losing its activity.

Oxidative Heck reaction of glycals and aryl hydrazines: a palladium-catalyzed C-glycosylation.

Abstract: An efficient Heck-type C-glycosylation of glycals via the C–N bond cleavage of aryl hydrazines has been developed. The flexibility of the reaction was tested by the substrate scope, consisting of glycals from different carbohydrate origins as well as aryl hydrazines with various substituents. Pure α-C-glycosides were obtained when (3R)-glycals were employed, whereas α,β mixtures were observed with (3S)-glycals.

A green approach for the synthesis of palladium nanoparticles supported on pectin: Application as a catalyst for solvent-free Mizoroki–Heck reaction

Abstract: A green method for the synthesis of palladium nanoparticles supported on pectin has been described. The synthesized nanoparticles were explored in Mizoroki–Heck reaction between different aryl halides and n-butyl acrylate under solvent-free conditions. The catalyst can be recycled for six runs without significant loss in the catalytic activity.

Harnessing reversible oxidative addition: application of diiodinated aromatic compounds in the carboiodination process.

Abstract: An I for an I: Conditions for the intramolecular carboiodination and the simultaneous convergent intramolecular carboiodination/intermolecular Heck reaction of various diiodoarenes were developed. The ability of the Pd(0)/QPhos catalyst/ligand combination to undergo reversible oxidative addition allows these reactions to proceed well, thus increasing both the appeal and utility of this class of substrates in site-selective cross-coupling reactions.

The role of palladium dynamics in the surface catalysis of coupling reactions.

Abstract: Ever since its discovery, the carbon–carbon cross-coupling reaction has contributed greatly to increasing the chemical complexity of molecules, which is crucial for organic synthesis and pharmaceutical drug development. Surface-catalyzing carbon–carbon bond formation on supported Pd nanoparticles (PdNPs) can decrease product contamination and aid the development of “greener” routes in organic synthesis. On the nanoscale, unlike in the bulk phase, PdNPs exhibit a large specific surface area and have abundant low coordination sites that enable increased catalytic activity. However, the catalytic reaction mechanisms on supported PdNPs surfaces remain a controversial topic of discussion. Some reports suggest that surface sites on PdNPs may play a crucial role in catalyzing coupling reactions, while others propose that the Pd species leached from support into solution govern the reaction pathways. Surface analysis of supported PdNPs used during crosscoupling reactions with atomic precision is difficult. Recent work suggests that PdNPs smaller than 1 nm are commonly missed during most microscopic studies. In addition, signal collection on highly dispersed particles after cross-coupling reactions is challenging owing to geometric and electric interference with the surface of bulk support. Herein, we set out to investigate the catalytic performance of PdNPs, in the Suzuki–Miyaura reaction, supported on materials with various levels of functionalization. The Pd dynamics were investigated in terms of changes to the surface of the PdNPs and to the support and correlated with catalytic results. Unlike previous reports applying active carbon, silica, alumina, or zeolites in the heterogeneous catalysis of coupling reactions, the current work exploits functionalized carbon nanotubes (CNTs) as a support. To study the influence of the chemical properties of the supporting materials on the Pd dynamics, CNTs were functionalized to different degrees before being loaded with PdNPs for use in coupling reactions. After synthesis the CNTs underwent annealing treatments at 700 8C and 1500 8C to improve the graphitization. For functionalization the CNTs were added to vigorously stirred concentrated nitric acid at 120 8C. CNTs annealed at 700 8C have more defects than CNTs annealed at 1500 8C, HNO3 treatment introduced a high functionalization (HCNTs) on defective CNTs and a low functionalization (LCNTs) on graphitized CNTs. The functionalities act as sites for anchoring metal cations during impregnation. Vacancies and cavities in the CNTs may also play entrap PdNP precursors. The STEM image in Figure 1a shows the dispersion of PdNPs (2% wt palladium) on H-CNTs (Pd/H-CNTs) with a size distribution of (1.8 0.2) nm. Figure 1b shows a poor dispersion of PdNPs (2% wt palladium) on L-CNTs (Pd/LCNTs) with a larger size distribution of (14.5 0.2) nm. Figure 1c shows plots of conversion versus reaction time for the Suzuki–Miyaura reaction of iodobenzene with phenylboronic acid in the presence of these PdNP/CNT catalysts. Quantitative conversion was obtained within one hour when Pd/H-CNTs was used, whereas reactions with Pd/L-CNTs required 8 h to reach quantitative conversion. The turnover frequency (TOF) at completion of the reaction is 990 h 1 for Pd/H-CNTs and 124 h 1 for Pd/L-CNTs. Figure 1d shows the Suzuki–Miyaura reaction solution of Pd/H-CNTs after one hour reaction time. This black solution could be left to stand for 10 min and no precipitate was observed. Filtration using normal filter papers collected all the Pd/H-CNTs and result in a clear filtrate (Figure 1e). The reaction solution of Pd/LCNTs after one hour reaction time, precipitated completely on being allowed to stand for 10 min (Figure 1 f). The significant differences in reactivity prompted a detailed analysis of the catalysts by electron microscopy. Reactions were stopped at 1 hour for Pd/H-CNTs and Pd/LCNTs. Although the majority H-CNTs were intact (Supporting Information, Figure S1), some showed damage after catalyzing the coupling reaction. The morphology changes to the Pd/H-CNTs are shown in Figure 2a,b. The STEM image in Figure 2a shows the dispersion of PdNPs on a structurally damaged H-CNT. Although some PdNPs have a larger size, PdNPs with a diameter of 1–2 nm are still visible. A detailed view of the damaged H-CNTs after reaction, was obtained by TEM (Figure 2b). “Tracks” from the movement [*] Dr. L. Shao, Dr. B. Zhang, Dr. W. Zhang, Prof. Dr. R. Schlcgl, Dr. D. S. Su Fritz Haber Institute of the Max Planck Society Faradayweg 4–6, 14195 Berlin (Germany) E-mail: dangsheng@fhi-berlin.mpg.de Homepage: www.fhi-berlin.mpg.de

Rational design and synthesis of hybrid porous polymers derived from polyhedral oligomeric silsesquioxanes via heck coupling reactions.

Abstract: Heck coupling reactions are introduced as an efficient method to prepare porous polymers. Novel inorganic-organic hybrid porous polymers (HPPs) were constructed via Heck coupling reactions from cubic functional polyhedral oligomeric silsesquioxanes (POSS), iodinated octaphenylsilsesquioxanes (OPS) and octavinylsilsesquioxanes (OVS) using Pd(OAc)2 /PPh3 as the catalyst. Here, two iodinated OPS were used, IOPS and p-I8 OPS. IOPS was a mixture with 90% octasubstituted OPS (I8 ) and some nonasubstituted OPS (I9 ), while p-I8 OPS was a nearly pure compound with ≥99% I8 and ≥93% para-substitution. IOPS and p-I8 OPS reacted with OVS to produce the porous materials HPP-1 and HPP-2, which exhibited comparable specific surface areas with SBET of 418 ± 20 m(2) g(-1) and 382 ± 20 m(2) g(-1) , respectively, with total pore volumes of 0.28 ± 0.01 cm(3) g(-1) and 0.23 ± 0.01 cm(3) g(-1) , respectively. HPP-1 showed a broader pore size distribution and possessed a more significant contribution from the mesopores, when compared with HPP-2, thereby indicating that IOPS may induce more disorder because of the geometrical asymmetry. HPP-1 and HPP-2 possessed moderate carbon dioxide uptakes of 134 and 124 cm(3) g(-1) at 1 bar at 195 K, making them promising candidates for CO2 capture and storage. The synthesized porous polymers may be easily post-functionalized using the retained ethenylene groups.

Preparation of Vinyl Silyl Ethers and Disiloxanes via the Silyl-Heck Reaction of Silyl Ditriflates

Abstract: Vinyl silyl ethers and disiloxanes can now be prepared from aryl-substituted alkenes and related substrates using a silyl-Heck reaction. The reaction employs a commercially available catalyst system and mild conditions. This work represents a highly practical means of accessing diverse classes of vinyl silyl ether substrates in an efficient and direct manner with complete regiomeric and geometric selectivity.

Hybrid networks constructed from tetrahedral silicon-centered precursors and cubic POSS-based building blocks via Heck reaction: porosity, gas sorption, and luminescence

Abstract: Cubic octavinylsilsesquioxane successively reacts with different tetrahedral silicon-centered precursors containing di-, tri-, or tetrabromophenyl groups to prepare hybrid porous polymers (HPPs) via Heck reaction. The resulting materials possess high porosities with Brunauer–Emmett–Teller specific surface areas of up to 875 m2 g−1. Their porosities can be tuned by altering the number of the connecting sites of silicon-centered units. For gas storage applications, HPP-5 exhibits the following properties: a high H2 uptake of 7.76 mmol g−1 (1.56 wt%) at 77 K and 1.01 bar; a moderate CO2 uptake of 1.04 mmol g−1 (4.58 wt%) at 298 K and 1.04 bar; and a low CH4 uptake of 0.28 mmol g−1 (0.45 wt%) at 298 K and 1 bar. These results suggest that these polymers can be applied as promising materials for H2 and CO2 storage as well as the selective adsorbents of CO2 rather than CH4. These polymers are also luminescent with the maximum emission at ca. 420 nm in the solid state; therefore, they could be potentially applied as blue light-emitting materials.

Nanoparticles of palladium supported on bacterial biomass: New re-usable heterogeneous catalyst with comparable activity to homogeneous colloidal Pd in the Heck reaction

Abstract: The Heck coupling of iodobenzene with ethyl acrylate or styrene was used to assess the catalytic properties of biogenic nanoparticles of palladium supported upon the surface of bacterial biomass (bioPd), this approach combining advantages of both homogeneous and heterogeneous catalysts. The biomaterial was comparably active or superior to colloidal Pd in the Heck reaction, giving a final conversion of 85% halide and initial rate of 0.17 mmol/min for the coupling of styrene and iodobenzene compared to a final conversion of 70% and initial rate of 0.15 mmol/min for a colloidal Pd catalyst under the same reaction conditions at 0.5 mol.% catalyst loading. It was easily separated from the products under gravity or by filtration for reuse with low loss or agglomeration. When compared to two alternative palladium catalysts, commercial 5% Pd/C and tetraalkylammonium-stabilised palladium clusters, the bioPd was successfully reused in six sequential alkylations with only slight decreases in the rate of reaction as compared to virgin catalyst (initial rate normalised for g Pd decreased by 5% by the 6th run with bioPd catalyst cf. a decrease of 95% for Pd/C). A re-usable Pd-catalyst made cheaply from bacteria left over from other processes would impact on both conservation of primary sources via reduced metal losses in industrial application and the large environmental demand of primary processing from ores.

The Clicked Pyridyl‐Triazole Ligand: From Homogeneous to Robust, Recyclable Heterogeneous Mono‐ and Polymetallic Palladium Catalysts for Efficient Suzuki–Miyaura, Sonogashira, and Heck Reactions

Abstract: Various mono- and polymetallic palladium complexes containing a 2-pyridyl-1,2,3-triazole (pyta) ligand or a nonabranch-derived (nonapyta) ligand have been synthesized by reaction of palladium acetate with these ligands according to a 1:1 metal-ligand stoichiometry and used as catalysts for carbon-carbon cross-coupling including the Suzuki–Miyaura, Sonogashira and Heck reactions. The unsubstituted monopalladium and nonapalladium complexes were insoluble in all the reaction media, whereas tri- and tetranuclar palladium complexes were soluble, which allowed conducting catalysis under either homogeneous or heterogeneous conditions. The organopalladium complexes were characterized by standard analytical and spectroscopic methods and by thermogravimetry showing decomposition above 110 °C. Both types of catalysts showed excellent activity for these cross carbon-carbon bond formations involving aryl halides including activated aryl chlorides or acyl chloride. Besides the comparison between homogeneous and heterogeneous catalysis, the key feature of these catalysts is their remarkable robustness that allowed recycling at least ten times in the example of the Heck reaction with excellent yields and without significant reduction of the conversion.

Oxidative Heck Vinylation for the Synthesis of Complex Dienes and Polyenes

Abstract: We introduce an oxidative Heck reaction for selective complex diene and polyene formation. The reaction proceeds via oxidative Pd(II)/sulfoxide catalysis that retards palladium-hydride isomerizations which previously limited the Heck manifold’s capacity for furnishing stereodefined conjugated dienes. Limiting quantities of nonactivated terminal olefins (1 equiv) and slight excesses of vinyl boronic esters (1.5 equiv) that feature diverse functionality can be used to furnish complex dienes and polyenes in good yields and excellent selectivities (generally E:Z = >20:1; internal:terminal = >20:1). Because this reaction only requires prior activation of a single vinylic carbon, improvements in efficiency are observed for synthetic sequences relative to ones featuring reactions that require activation of both coupling partners.

Palladium‐Containing Ionic Liquid‐Based Ordered Mesoporous Organosilica: An Efficient and Reusable Catalyst for the Heck Reaction

Abstract: Aryl iodides and bromides and as well as aryl chlorides bearing electron-withdrawing groups can be used in the Heck coupling reaction.

Flow Chemistry Syntheses of Styrenes, Unsymmetrical Stilbenes and Branched Aldehydes

Abstract: Two tandem flow chemistry processes have been developed. A single palladium-catalysed Heck reaction with ethylene gas provides an efficient synthesis for functionalised styrenes. Through further elaboration the catalyst becomes multi-functional and performs a second Heck reaction providing a single continuous process for the synthesis of unsymmetrical stilbenes. In addition, the continuous, rhodium-catalysed, hydroformylation of styrene derivatives with syngas affords branched aldehydes with good selectivity. Incorporation of an in-line aqueous wash and liquid–liquid separation allowed for the ethylene Heck reaction to be telescoped into the hydroformylation step such that a single flow synthesis of branched aldehydes directly from aryl iodides was achieved. The tube-in-tube semi-permeable membrane-based gas reactor and liquid–liquid separator both play an essential role in enabling these telescoped flow processes.