Synthesis, characterization, structure and catalytic activity of (NNN) tridentate azo-imine nickel(II), palladium(II) and platinum(II) complexes

The newly designed tridentate ligand, 2,2′-(bisdiamino)azobenzene, H₂L, 1 derived from the oxidative coupling of o-phenylenediamine in presence of NaOH base, upon reaction with Ni(II), Pd(II) and Pt(II) separately in methanol yielded [(HL)Ni(PPh₃)]ClO₄, 2, [(HL)Pd(PPh₃)]ClO₄, 3 and [(L)Pt(PPh₃)], 4 which were characterized by spectral data and authenticated by single crystal X-ray diffraction of 1-4. The diffraction analysis revealed that the ligand binds the metals (Ni(II), Pd(II)) in monoanionic and Pt(II) in dianionic tridentate (N,N,N) fashion offering distorted square planar geometry where fourth position is occupied by one PPh₃group. One ClO₄^-ion satisfies the charge of the former aggregate [(HL)Ni(PPh₃)]⁺and [(HL)Pd(PPh₃)]⁺. Suzuki and Heck coupling reactions were carried out, in presence of air and moisture, using [(HL)Pd(PPh₃)]ClO₄, 3 as catalysts for a variety of substrates.