Platinum and Palladium Complexes Containing Cationic Ligands as Catalysts for Arene H/D Exchange and Oxidation

Abstract

Cationic catalysts in HD: Palladium(II) and platinum(II) complexes of pyridinium‐substituted bipyridine ligands are highly active and stable catalysts for H/D exchange and oxidation of aromatic CH bonds (TONs up to 3200, TOFs up to 0.1 s−1; see scheme, EWG=electron‐withdrawing group, EDG=electron‐donating group).

Ohne dirigierende Gruppen: übergangsmetallkatalysierte C‐H‐Aktivierung einfacher Arene

“…[101] Sanford und Mitarbeiter fanden kürzlich mit dem Einsatz eines Pd(OAc) 2 /Pyridin-Katalysatorsystems deutlich bessere Reaktionsbedingungen für diese Reaktion. [102,103] Das Metall/ Ligand-Verhältnis hatte einen starken Einfluss auf die Effizienz der Reaktion, die mit 0.9 ¾quivalenten Pyridin pro Pd(OAc) 2 -¾quivalent die hçchsten Ausbeuten der acetoxylierten Produkte lieferte. Die Reaktivität wurde in diesem Fall auf die In-situ-Erzeugung eines aktiven Pd II -Katalysators der Form [(py)Pd II (OAc) 2 ] zurückgeführt, der über eine freie Koordinationsstelle zur C-H-Aktivierung verfügt.…”

Remarkably High Reactivity of Pd(OAc)2/Pyridine Catalysts: Nondirected CH Oxygenation of Arenes

“…[1] In marked contrast, analogous CÀH oxidation reactions of substrates that do not contain directing groups remain challenging. [2][3][4][5][6][7] The lack of a directing group typically renders these transformations (as exemplified by C À H oxygenation) kinetically slow, particularly with electron-deficient arene substrates.…”

“…[1] In marked contrast, analogous CÀH oxidation reactions of substrates that do not contain directing groups remain challenging. [2][3][4][5][6][7] The lack of a directing group typically renders these transformations (as exemplified by C À H oxygenation) kinetically slow, particularly with electron-deficient arene substrates. [3d, 6, 7c] The palladium-catalyzed CÀH oxygenation of simple arenes is also plagued by low turnover numbers [3][4][5][6] and competing biaryl formation, which often leads to catalyst decomposition through precipitation of palladium black.…”

“…[5] Furthermore, with substituted aromatic substrates, the site selectivity is typically low and difficult to control. As part of a program aimed at developing efficient, selective, and robust catalysts for nondirected CÀH functionalization reactions, [7] we sought to identify supporting ligands that would address these limitations and promote the Pd II/IVcatalyzed C À H acetoxylation of arenes.…”

Recent advances in the application of group-10 transition metal based catalysts in C–H activation and functionalization

“…In spite of this, the high cost of Pt and large amount of catalyst required restricted its applicability [74]. Prior to this, the same group reported the application of dicationic-bipyridinebased ligands in Pt-and Pd-catalyzed arene H/D exchange and oxidation reactions [77].…”