Palladium(II), platinum(II), ruthenium(II) and mercury(II) complexes of potentially tridentate Schiff base ligands of (E, N, O) type (E = S, Se, Te): Synthesis, crystal structures and applications in Heck and Suzuki coupling reactions

Schiff bases of 2-hydroxybenzophenone (HBP) (C6H5)(2-HOC6H4)CN(CH2)nEAr (L1/L2: E = S, Ar = Ph, n = 2/3; L3/L4: E = Se, Ar = Ph, n = 2/3; L5/L6: E = Te, Ar = 4-MeOC6H4, n = 2/3) and their complexes [PdCl(L-H)] (L = L1−L6; 1, 2, 3, 5, 7, 11), [PtCl(L3-H/L5-H)] (4/8), [PtCl2(L4/L6)2] (6/12), [(p-cymene)RuCl(L5/L6)]Cl (9/13) and [HgBr2(L5/L6)2] (10/14) have been synthesized and characterized by proton, carbon-13, selenium-77 and tellurium-125 NMR, IR and mass spectra. Single crystal structures of L1, 1, 3, 4, 5 and 7 were solved. The Pd–E bond distances (Å): 2.2563(6) (E = S), 2.3575(6)−2.392(2) (E = Se); 2.5117(5)−2.5198(5) (E = Te) are near the lower end of the bond length range known for them. The Pt–Se bond length, 2.3470(8) Å, is also closer to the short values reported so far. The Heck and Suzuki reaction were carried out using complexes 1, 3, 5 and 7 as catalysts under aerobic condition. The percentage yields for trans product in Heck reaction were found upto 85%.

Graphical abstractSchiff base ligands (C6H5)(2-HOC6H4)CN(CH2)nEAr (L; E = S/Se/Te; Ar = Ph/4-MeOC6H4, n = 2/3; and their complexes [Pd/PtCl(L-H)], [PtCl2(L)2], [(p-cymene) RuCl(L)]Cl and [HgBr2(L)2] have been synthesized and characterized by multinuclei NMR, IR and mass spectra and single crystal structure determination [Pd–S, 2.2563(6); Pd–Se, 2.3575(6)–2.392(2); Pd–Te, 2.5117(5)–2.5198(5); Pt–Se = 2.3470(8) Ǻ]. Pd-complexes were explored for Heck and Suzuki reactions.Figure optionsDownload full-size imageDownload as PowerPoint slide