Synthesis and characterization of cyclometallated complexes of benzalazines. Crystal and molecular structure of [{Pd(p-ClC6H3CHN–)Cl(PEt3)2}2]

Abstract

The reaction of benzalazines, (p-RC₆H₄CHN–)₂(R = H, Cl, NO₂, or NMe₂), with PdCl₂ leads in the the first two cases to the formation of cyclometallated polymeric species that react with phosphines to yield dimetallated compounds [{Pd(p-RC₆H₃CHN^–)Cl(PR′₃)₂}₂](R′= Et or Ph) and/or [{[graphic omitted]–)Cl(PPh₃)}₂]. Phosphine exchange reactions give the complex [{Pd(p-RC₆H₃CHN–)Cl(PEt₃)(PPh₃)}₂]. The molecular structure of [{Pd(p-ClC₆H₃CHN^–)Cl(PEt₃)₂}₂] has been determined by a single-crystal X-ray analysis. The crystals are monoclinic, space group P2₁/n, a= 11.124(3), b= 10.062(2), c= 22.566(5)Å, β= 102.95(3)°, and Z= 2; R= 0.052 for 3 306 reflections. Palladium atoms are five-co-ordinated, the Pd–N distance being 2.743 Å. However, n.m.r. spectra show that, in solution, free rotation around the C(aromatic)–C(azomethine) bonds does occur even at –100 °C.