Microwave assisted Suzuki-Miyaura and Mizoroki-Heck cross-couplings catalyzed by non-symmetric Pd(II) CNS pincers supported by iminophosphorane ligands

Two new Pd-II non-symmetrical CNS pincer type complexes [PdCl{C6H4(Ph2P = NC6H4SR-k(3)-C, N, S)}] [R = Bn (3) and 4-C6H5NO2 (4)], supported by iminophosphorane ligands functionalized with a thioether moiety, were prepared and fully characterized. These compounds and the already known complexes 1 (R = Me) and 2 (R = Ph) were evaluated as catalysts in microwave assisted Suzuki-Miyaura and Mizoroki-Heck coupling reactions. Whereas compound 1 instantaneously decomposed under MW irradiation, as visible black Pd-0 precipitated in both processes, compounds 2-4 showed good conversions without apparent decomposition. The coupling reactions were dramatically accelerated under MW radiation when compared to conventional heating, with 3 (R = 4-C6H4NO2) showing the highest catalytic efficiency of all in both processes. The catalytic activity of complex 2 was further examined in the two cross-couplings with a series of para-substituted bromo-benzenes. Both catalyses proceeded under normal aerobic conditions and were not affected by an excess of elemental Hg. The Mizoroki-Heck reaction operated with high regioselectivity, yielding only the linear 1,2-products. (C) 2017 Elsevier B.V. All rights reserved.