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

Abstract

Three pendant benzamidines, [Ph-C(=NC6H5)-{NH(E)}] [E = -(CH2)(2)SMe (1); -(CH2)(2)(SBu)-Bu-t (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(eta(1)-C6H4)} {=N(E)}]Pd(OAc) [E = -(CH2)(2)SMe (4); -(CH2)(2)(SBu)-Bu-t (5); -o-C6H4SMe (6)], as mononuclear palladium complexes respectively. A minor product described as 5', {[Ph-C{-N(C6H5)} {-N(CH2)(2)(SBu)-Bu-t}]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(eta(1)-C6H4)}{=N(E)}]PdCl [E = -(CH2)(2)SMe (7); -(CH2)(2)(SBu)-Bu-t (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.