Gerard K. M. Verzijl

Heck Reactions without Salt Formation : Aromatic Carboxylic Anhydrides as Arylating Agents

Environmentally benign and economical production of arylated olefins can be achieved by a new variant of the Heck reaction in which no halogen salts are formed. The trick is the use of aromatic carboxylic anhydrides 1 as arylating agents. With halide-activated palladium chloride as catalyst, which requires no phosphane ligands, the olefins 2 can be prepared according to Equation (a) in good yields.

Heck‐Reaktionen ohne Salzbildung: aromatische Carbonsäureanhydride als Arylierungsmittel

Umweltfreundlich und okonomisch kann eine Vielzahl von arylierten Olefinen durch eine neue Variante der Heck-Reaktion synthetisiert werden, bei der keine Halogenid-Salze entstehen. Entscheidend ist die Verwendung aromatischer Carbonsaureanhydride 1 als Arylierungsmittel. Mit Halogenid-aktiviertem Palladiumchlorid als Katalysator, der keine Phosphanliganden erfordert, lassen sich nach Gleichung (a) die Olefine 2 in guten Ausbeuten herstellen.

Palladium‐Catalyzed Cross‐Dehydrogenative Coupling of o‐Xylene: Evidence of a New Rate‐Limiting Step in the Search for Industrially Relevant Conditions

An efficient cross‐dehydrogenative coupling of o‐xylene under neat conditions, which brings important industrial benefits towards the synthesis of a monomer used in polyimide resins, is reported. The catalyst based on the combination of Pd/N ligand/carboxylate=1:1:2 does not require a Cu cocatalyst and proceeds at 11 bar of O2 pressure. Evaluation of the deuterium kinetic isotope effect (KIE) provides evidence for three different rate‐determining steps, which depend on the reaction conditions (medium, temperature). Under the reported neat conditions, the dissociation of a carboxylate‐bridged dimer to generate a more reactive monometallic Pd species is proposed to be the rate‐limiting step.