Palladacycles as Reactive Intermediates

Storable N-phenylcarbamate palladacycles for rapid functionalization of an alkyne-encoded protein

Here we report the synthesis of storable N-phenylcarbamate palladacycles that showed robust reactivity in the cross-coupling reaction with an alkyne-encoded protein with a second-order rate constant approaching 19 770 ± 930 M(-1) s(-1).

Palladium-nanoparticle-catalyzed 1,7-palladium migration involving C-H activation, followed by intramolecular amination: regioselective synthesis of N1-arylbenzotriazoles and an evaluation of their inhibitory activity toward indoleamine 2,3-dioxygenase

A sulfur-modified gold-supported palladium material (SAPd) has been developed bearing palladium nanoparticles on its surface. Herein, we report for the first time the use of SAPd to affect a Pd-nanoparticle-catalyzed 1,7-Pd migration reaction for the synthesis of benzotriazoles via C-H bond activation. The resulting benzotriazoles were evaluated in terms of their inhibitory activity toward indoleamine 2,3-dioxygenase.

Cyclopalladation of telluro ether ligands: synthesis, reactivity and structural characterization

Reactions of telluro ethers with common cyclopalladation precursors gave a variety of palladium complexes ranging from mononuclear,trans-[PdCl₂(TeR₂)₂] to binuclear [Pd₂(μ-Cl)₂Cl₂(TeRR′)₂], cyclopalladated [Pd₂(μ-OAc)₂{RTeCH₂C₆H₂(4,6-Me₂)}₂] and products formed by Te–C bond cleavage.

Oxime palladacycles revisited: stone-stable complexes nonetheless very active catalysts

Our review critically presents the main achievements, advantages, and limitations of oxime palladacycles as high-turnover catalysts for Heck, as well as homo- and cross-coupling reactions such as Suzuki-Miyaura, Stille, Ullmann-type, Cassar-Heck-Sonogashira, sila-Sonogashira, Glaser-type, Hiyama, and alkoxycarbonylation reactions. New developments in this area are reviewed from a mechanistic and synthetic point of view. The role of oxime palladacycles as a source of highly active zero-valent palladium species is also discussed.

Cyclometalation vs. Werner-type coordination of sterically enforced palladium(ii)-1,3-bis(pyridyl-2-imino)isoindolines (Pd-BPIs)

The reaction of 1,3-bis(4,6-dimethylpyridyl-2-imino)isoindoline and palladium acetate in methanol selectively yields the expected acetato palladium N,N,N-chelate or a cyclometalated tetranuclear dimer depending on the stoichiometry of the reactants.

Sequential Unsymmetrical Aryl Coupling of o-Substituted Aryl Iodides with o-Bromophenols and Reaction with Olefins: Palladium-Catalyzed Synthesis of 6H-Dibenzopyran Derivatives

Dibenzopyran derivatives are prepared by palladium- and norbornene-catalyzed reaction of aryl iodides, o-substituted with electron-releasing substituents, o-bromophenols, and activated alkenes.

Understanding Sulfone Behavior in Palladium-Catalyzed Domino Reactions with Aryl Iodides

Unlike traditionally used acyclic 1,2-disubstituted alkenes, the reaction of alpha,beta-unsaturated phenyl sulfones with aryl iodides under Heck reaction conditions takes place mainly by means of a four-component domino process, involving one unit of the alkene and three units of the aryl iodide, affording substituted 9-phenylsulfonyl-9,10-dihydrophenanthrenes. We report here the results of a computational study on the mechanism of this domino arylation reaction. Based on these results we can explain why vinyl sulfones, unlike other electron-deficient alkenes such as enones, preferentially follow this domino pathway instead of the usual Heck pathway. The key step is a C-H activation process in which a five-membered palladacycle is formed. The greater ability of vinyl sulfones, relative to enones, to reach the transition state that leads to the formation of the initial palladacycle makes the difference.

Low-Valent Niobium-Mediated Double Activation of C−F/C−H Bonds: Fluorene Synthesis fromo-Arylated α,α,α-Trifluorotoluene Derivatives

By the treatment of 0.3 molar amount of NbCl5 and LiAlH4, o-arylated alpha,alpha,alpha-trifluorotoluenes afforded fluorene derivatives in good yields. C-F bonds of the CF3 group and the neighboring ortho C-H bond were doubly activated to give the coupling products.

Palladium-catalyzed arylation of alpha,alpha-disubstituted arylmethanols via cleavage of a C-C or a C-H bond to give biaryls

The palladium-catalyzed arylation of alpha,alpha-disubstituted arylmethanols with aryl halides proceeds not only via C-H bond cleavage at the ortho-position, but also via cleavage of the sp(2)-sp(3) C-C bond with the liberation of ketones (beta-carbon elimination) to give the corresponding biaryls. Both reactions appear to occur through common arylpalladium(II) alcoholate intermediates. The results of systematic studies with respect to which C-C or C-H bond is preferentially cleaved in the arylation are reported. Among the important findings is the selective elimination of ortho-substituted aryl groups even from aryl(diphenyl)methanols due to steric reasons. Thus, various biaryls having ortho-substituents can be produced efficiently by treatment of the corresponding aryl(diphenyl or dimethyl)methanols with aryl bromides and chlorides.

Palladium-catalyzed multiple arylation of thiophenes

Secondary 2-thiophenecarboxamides efficiently undergo unique triarylation accompanied by formal decarbamoylation under palladium catalysis. 3-Substituted thiophenes, especially having an electron-withdrawing group, can also be triarylated.