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Direct (Hetero)Arylation Polymerization for the Preparation of Conjugated Polymers
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
J. Terence Blaskovits, Mario Leclerc
The reaction begins by the generation of the active Pd(0) catalyst. This occurs either via the exchange of ligands on a Pd(0) precatalyst (such as Pd2dba3 or Pd(PCy3)2, where Cy = cyclohexyl and dba = dibenzylideneacetone) or via the reduction of a Pd(II) precatalyst (e.g. PdCl2, Pd(OAc)2), for example via the oxidation of a phosphine ligand or the formation of a C–C bond from two C–H bonds.58–60OA on the C–X bond of bromobenzene leads to the first arylpalladium(II) intermediate 1. Ligand exchange between the halide and a carboxylate ion gives the bidentate complex 2. The CMD transition state consists of the inner-sphere deprotonation of thiophene by the carboxylate, which simultaneously frees a coordination site on the metal center for the approach of the thienyl substrate. This second part constitutes the metalation of the thiophene. Following the formation of the post-CMD intermediate (3), a number of possible ligand exchanges can occur in order to prepare for reductive elimination. For example, the carboxylic acid may de-coordinate and be replaced by another phosphine ligand (4, as shown) or remain coordinated in a monodentate fashion (5, Pathway 2). In either case, the carboxylic acid is reconverted to its conjugate base by way of an acid-base reaction with the carbonate additive (e.g. cesium carbonate, Cs2CO3, shown here). During the reductive elimination of the phenyl and thienyl fragments, a new C–C bond is formed and the initial Pd(0) species is regenerated.
Interfacial Catalysis at Oil/Water Interfaces
Published in Alexander G. Vdlkdv, Interfacial Catalysis, 2002
Cuprous chloride tends to form water-soluble complexes with lower olefins and acts as an IPTC catalyst, e.g., in the two-phase hydrolysis of alkyl chlorides to alcohols with sodium carboxylate solution [10,151] and in the Prins reactions between 1-alkenes and aqueous formaldehyde in the presence of HCl to form 1,3 -glycols [10]. Similarly, water-soluble rhodium-based catalysts (4-diphenylphosphinobenzoic acid and tri- C8-10-alkylmethylammonium chlorides) were used as IPTC catalysts for the hydroformylation of hexene, dodecene, and hexadecene to produce aldehydes for the fine chemicals market [152]. Palladium diphenyl(potassium sulfonatobenzyl)phosphine and its oxide complexes catalyzed the IPTC dehalogenation reactions of allyl and benzyl halides [153]. Allylic substrates such as cinnamyl ethyl carbonate and nucleophiles such as ethyl acetoactate and acetyl acetone catalyzed by a water-soluble bis(dibenzylideneacetone)palladium or palladium complex of sulfonated triphenylphosphine gave regio- and stereo-specific alkylation products in quantitative yields [154]. Ito et al. used a self-assembled nanocage as an IPTC catalyst for the Wacker oxidation of styrene catalyzed by ( en )PdNO3[155].
Pd2(dba)3-catalyzed amination of C5-bromo-imidazo[2,1-b][1,3,4] thiadiazole with substituted anilines at conventional heating in Schlenk tube
Published in Journal of Sulfur Chemistry, 2021
Plausible mechanism: Based on our results and previous literature reports, [15,16] the plausible reaction mechanism for the generation of title compounds was proposed. The active palladium species [Pd(Xantphos)]0 is generated upon coordination of ligand (Xantphos) with Pd(0) by the replacement of dibenzylideneacetone ligands of [Pd2(dba)3]0 [12]. The oxidative addition of 5-bromo-2-phenylimidazo[2,1-b][1,3,4]thiadiazole (6a) to [Pd(Xantphos)]0 forms intermediate I. Next, the coordination of PdII with CsCO3- occurs after displacement of bromide, which leads to the formation of intermediate II. Subsequently, the displacement of CsCO3- with hydrogen from aniline (7) leads to the liberation of cesium bicarbonate and forms intermediate III. Ultimately, the C–N bond formation takes place while reducing PdII to Pd0 with the elimination of product (8) and subsequent regeneration of the active Pd0 species (Figure 5)
The role of 8-quinolinyl moieties in tuning the reactivity of palladium(II) complexes: a kinetic and mechanistic study
Published in Journal of Coordination Chemistry, 2019
Daniel O. Onunga, Deogratius Jaganyi, Allen Mambanda
All syntheses were done under nitrogen. RAC-2,2′-bis(diphenylphosphino)-1,10-binaphthyl (97%), 8-aminoquinoline (98%), 8-bromoquinoline (98%), NaOtBu (97%), 2-picolylchloride hydrochloride (98%), pyridine-2-carboxyaldehyde (99%), tris(dibenzylideneacetone)-dipalladium(0) (97%), lithium perchlorate (98%), potassium tetrachloropalladate (K2PdCl4 99.99%), dichloro-1,5-cyclooctadiene palladium(II) (Pd(COD)Cl2, 99%), thiourea nucleophiles, and the ligand, di-(2-picolyl)amine were all purchased from Aldrich and used as received. Solvents were distilled before use and dried through standard procedures [41].
An insight on the different synthetic routes for the facile synthesis of O/S-donor carbamide/thiocarbamide analogs and their miscellaneous pharmacodynamic applications
Published in Journal of Sulfur Chemistry, 2023
Faiza Asghar, Bushra Shakoor, Babar Murtaza, Ian S. Butler
Using a catalyst system based on trist(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3 and ligand, an analysis of various cyanate sources publicized that while both KOCN and AgOCN were incompetent for this conversion, the usage of NaOCN resulted in the synthesis of the desired product, though in low yield. Vinogradova et al. [38] reasoned that a more proficient synthesis of the active catalytic species prior to its addition into the reaction slurry will result in an improved yield, because the isocyanate anion has the potential to hinder catalytic activity.