Adriano Indolese

Supported palladium catalysts for fine chemicals synthesis

Abstract The contribution reviews the application of heterogeneous Pd catalysts for the manufacture of fine chemicals with special emphasis of their organic synthetic potential. In a first part, some background is given on the scope and limitations of homogeneous and heterogeneous catalysis and on significant parameters and the various types of supported Pd catalysts. Then, the application of supported Pd catalysts for important classes of transformations are reviewed organized according to reaction type. The general statements are illustrated with relevant examples from the literature and from our own laboratories. Hydrogenation, hydrogenolysis, and dehydrogenation reactions are considered to be mature technologies with an extremely broad scope both for small-scale laboratory applications and large to very large-scale manufacturing processes. Oxidation reactions and CC coupling reactions usually have a rather narrow scope and only relatively few have been developed to the technical stage. Especially for CC coupling reactions, the nature of the active Pd species is under debate because it is not clear whether the reaction takes place on the metallic surface or whether leached soluble Pd complexes are the active catalysts.

SUZUKI-TYPE COUPLING OF CHLOROARENES WITH ARYLBORONIC ACIDS CATALYSED BY NICKEL COMPLEXES

A Suzuki-type cross-coupling reaction of aryl chlorides with arylboronic acids using nickel-catalysts is described. The best results were obtained at 95 °C in the presence of K3PO4 and in dioxane using Ni(dppf)Cl2. Unsymmetrical biaryls with both electron-withdrawing and electron-donating functional groups were obtained in high yields.

A More Efficient Catalyst for the Carbonylation of Chloroarenes

The right ligand enables the efficient carbonylation of unactivated chloroarenes. A general synthesis of benzoic acid derivatives is possible with the palladium-ferrocenylphosphane catalysts.

Palladium-catalyzed carbonylation of aryl halides — a detailed investigation of the alkoxycarbonylation of 4-bromoacetophenone ☆

Abstract The palladium-catalyzed alkoxycarbonylation of 4-bromoacetophenone with n-butanol to give the corresponding benzoic acid ester has been studied systematically by evaluating the influence of critical reaction parameters such as temperature, CO pressure, solvent, base, catalyst precursor and ligand/palladium ratio. The highest catalyst efficiency was displayed at 130°C and low CO pressures using the neat alcohol as the solvent, a trialkylamine as the base and Pd(PPh3)4 or a PdCl2(PhCN)2/n PPh3-combination as the catalyst precursor. A strong dependence of the catalyst activity and stability on the phosphine concentration in the reaction mixture was found as demonstrated by the time/conversion behavior of the reaction. Thus, under the optimized conditions, catalyst productivities (turnover number=TON) of up to 7000 (70% yield of 2) were achieved.

First Application of Secondary Phosphines as Supporting Ligands for the Palladium-Catalyzed Heck Reaction: Efficient Activation of Aryl Chlorides

Secondary dialkylphosphines were successfully used for the first time as efficient supporting ligands for the palladium-catalyzed Heck reaction of electron-rich and electron-poor aryl chlorides with olefins such as acrylate, ethylene, styrene, and n-butyl vinyl ether. The yields with HP(t-butyl)2 and HP(adamantyl)2 were comparable or better than those obtained with known systems of tertiary phosphines such as P(cyclohexyl)3 and P(t-butyl)3, especially at a catalyst loading of <1 mol %. In comparison with tertiary phosphines, the secondary phosphines have the advantage of being readily available at low cost on a technical scale, and are comparable with respect to handling and oxygen sensitivity.

Aryldiones incorporating a [1,4,5]oxadiazepane ring. Part 2: Chemistry and biology of the cereal herbicide pinoxaden†

BACKGROUND Pinoxaden is a new cereal herbicide that provides outstanding levels of post-emergence activity against a broad spectrum of grass weed species for worldwide selective use in both wheat and barley. RESULTS Factors influencing activity and tolerance to pinoxaden were in part linked to distinct structural parts of the active ingredient. Three complementary contributions that decisively impact upon the herbicidal potency against grasses were identified: a preferred 2,6-diethyl-4-methyl aromatic substitution pattern, a dione area suitable for proherbicide formation and beneficial adjuvant effects. The uptake and translocation pattern of pinoxaden when coapplied with its tailored adjuvant were analysed by autoradiography, indicating extensive and rapid penetration, followed by effective distribution throughout the plant. Crop injury reduction on incorporation of the [1,4,5]oxadiazepane ring into the aryldione template was reinforced with safener technology. Comparative studies on the behaviour of pinoxaden applied either alone or in combination with the safener cloquintocet-mexyl demonstrated that addition of the safener resulted in significant enhancement of metabolic degradation in wheat and barley, providing excellent crop tolerance and a substantial selectivity margin without adverse effects on weed control. CONCLUSION The biological potential of pinoxaden and its active principle pinoxaden dione in terms of grass weed control and tolerance in cereals was fully exploited by inclusion of the safener cloquintocet-mexyl in the formulation in combination with a specific and tailor-made tank-mix adjuvant based on methylated rape seed oil.