New mono- and di-nuclear complexes of PdII, PtII and NiII of PNNP ligands with a 2,2′-biaryl bridging unit

The Schiff bases 2,2'-bis(N-[(2-diphenylphosphino)phenyl]formimidoyl}biphenyl (L-1) and 2,2'-bis{[(2-diphenylphosphino)benzylidene]amino}biphenyl (L-2) were synthesized from the appropriate amine and aldehyde. Their co-ordination behaviour towards Pd-II, Pt-II and Ni-II has been studied. Dinuclear complexes were formed when treating L-1 with 2 equivalents of [PdCl(Me)(cod)] (cod = cycloocta-1,5-diene) and Pd(O2CMe)(2). In the case of the reaction of L-1 with Pd(O2CMe)(2) an unexpected double cyclopalladated complex was formed. However, treatment of L-1 with 2 equivalents of [PtCl2(MeCN)(2)] resulted in hydrolysis of the ligand and a mononuclear complex of (2-diphenylphosphino)benzenamine was obtained. The structure of [(Pd2LCl2Me2)-Cl-1] 1 has been established by an X-ray diffraction study. The dihedral angle between the biphenyl rings is 49.2(8)degrees and the intramolecular Pd ... Pd distance is 7.165(3) Angstrom. The biphenyl bridging moiety shows a remarkable bending of 169.2(8)degrees. Treatment of 1 with carbon monoxide resulted in a double CO insertion, yielding the bis(acetyl)palladium compound [(Pd2LCl2)-Cl-1-{C(O)Me}(2)] 2. The structure of [Pd2L1(O2CMe)(2)]. 4CH(2)Cl(2) 3 was also determined by X-ray diffraction, The dihedral angle between the biphenyl rings is 75.9(14)degrees while the intramolecular Pd Pd distance is 8.655(2) Angstrom. The reaction of L-2 with 2 equivalents of anhydrous [PdCl2(MeCN)(2)] or NiCl2 afforded mononuclear complexes. The crystal and molecular structure of [PdL2]Cl-2 . 3.5CH(2)Cl(2) was determined. The compound has an approximately square-planar P2N2 geometry.