Metal‐Free and Pd II ‐Promoted [2+3] Cycloadditions of a Cyclic Nitrone to Phthalonitriles: Syntheses of Oxadiazolines as well as Phthalamide–Pd II and Dihydropyrrolyl‐iminoisoindolinone–Pd II Complexes with High Catalytic Activity in Suzuki–Miyaura Cross‐Coupling Reactions

The previously unknown reactions between phthalonitriles, 1,2‐(CN) 2 (C 6 )R 1 R 2 R 3 R 4 1 ( 1 a , R 1 =R 2 =R 3 =R 4 =H; 1 b , R 1 =R 2 =R 4 =H, R 3 =CH 3 ; 1 c , R 1 =R 4 =H, R 2 =R 3 =Cl; 1 d , R 1 =R 2 =R 3 =R 4 =Cl; 1 e , R 1 =R 2 =R 3 =R 4 =F), and a cyclic nitrone, − O + NCHCH 2 CH 2 C Me 2 2 , proceed under heating in a sealed tube to give phthalimides 3 , 2‐oxadiazolyl‐benzonitriles 4 or ortho ‐bis(oxadiazolyl)tetrafluorobenzene 4 e′ . In the presence of palladium(II) chloride, phthalonitriles 1 react with 2 at room temperature, to give bis(pyrrolidin‐2‐ylidene)phthalamide Pd II complexes 5 via metal‐promoted rupture of the NO bond of the oxadiazoline ring. The ketoimine ligands thus generated can be liberated from the metal by displacement with a diphosphine. Although the first [2+3] cycloaddition of 2 to 1 can occur in the absence of the metal to give the mono‐cycloadducts 4 , the second [2+3] coupling at the still‐unreacted cyano group requires its activation by coordination to Pd II , affording complexes 6 containing two ligated oxadiazolyl‐benzonitriles. These ligands undergo either i) further cycloaddition with 2 to afford ultimately (upon rearrangement) the bis(pyrrolidinylidene)phthalamide complexes 5 or ii) NO bond cleavage in the oxadiazoline ring with intramolecular attack of the imine nitrogen on the cyano carbon and bridging to a second Pd II center to afford dimeric palladium(II) complexes 7 , with chloride bridges, that bear a dihydropyrrolyl‐iminoisoindolinone, a new type of ligand. The compounds were characterized by IR, 1 H, and 13 C NMR spectroscopy, ESI MS or FAB + MS, elemental analyses and, in the case of 4 c , 5 a , 5 c , and 7 c , also by X‐ray diffraction analysis. Complexes 5 a and 7 c show high catalytic activity for the Suzuki–Miyaura cross‐coupling reaction of bromobenzene and phenylboronic acid and give biphenyl in high yields with turnover frequencies (TOFs) of up to 9.0×10 5  h −1 .