Palladacycles bearing tridentate CNS-type benzamidinate ligands as catalysts for cross-coupling reactions

Abstract

Three pendant benzamidines, [Ph–C(NC₆H₅)–{NH(E)}] [E = –(CH₂)₂SMe (1); –(CH₂)₂S^tBu (2); –o-C₆H₄SMe (3)], are described. Reactions of 1, 2 or 3 with one molar equivalent of Pd(OAc)₂ in CH₂Cl₂ give the palladacyclic complexes, [Ph–C{–NH(η¹-C₆H₄)}{N(E)}]Pd(OAc) [E = –(CH₂)₂SMe (4); –(CH₂)₂S^tBu (5); –o-C₆H₄SMe (6)], as mononuclear palladium complexes respectively. A minor product described as 5′, {[Ph–C{–N(C₆H₅)}{–N(CH₂)₂S^tBu}]Pd(OAc)}₂, was isolated as benzamidinate-bridged dinuclear palladium complex upon recrystallizing from Et₂O/hexane solution. Treatment of 1, 2 or 3 with one molar equivalent of PdCl₂ in the presence of NEt₃ in CH₂Cl₂ gives the palladacyclic complexes, [Ph–C{–NH(η¹-C₆H₄)}{N(E)}]PdCl [E = –(CH₂)₂SMe (7); –(CH₂)₂S^tBu (8); –o-C₆H₄SMe (9)], as mononuclear palladium complexes respectively. The crystal and molecular structures are reported for compounds 5, 5′ and 6–8. The application of these palladacyclic complexes to the Suzuki and Heck coupling reactions was examined.