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

Abstract

Three pendant benzamidines, [Ph-C(=NC(6)H(5))-{NH(E)}] [E = -(CH(2))(2)SMe (1); -(CH(2))(2)S(t)Bu (2); -o-C(6)H(4)SMe (3)], are described. Reactions of 1, 2 or 3 with one molar equivalent of Pd(OAc)(2) in CH(2)Cl(2) give the palladacyclic complexes, [Ph-C{-NH(η(1)-C(6)H(4))}{=N(E)}]Pd(OAc) [E = -(CH(2))(2)SMe (4); -(CH(2))(2)S(t)Bu (5); -o-C(6)H(4)SMe (6)], as mononuclear palladium complexes respectively. A minor product described as 5', {[Ph-C{-N(C(6)H(5))}{-N(CH(2))(2)S(t)Bu}]Pd(OAc)}(2), was isolated as benzamidinate-bridged dinuclear palladium complex upon recrystallizing from Et(2)O/hexane solution. Treatment of 1, 2 or 3 with one molar equivalent of PdCl(2) in the presence of NEt(3) in CH(2)Cl(2) gives the palladacyclic complexes, [Ph-C{-NH(η(1)-C(6)H(4))}{=N(E)}]PdCl [E = -(CH(2))(2)SMe (7); -(CH(2))(2)S(t)Bu (8); -o-C(6)H(4)SMe (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.