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 (L1) and 2,2′-bis{[(2-diphenylphosphino)benzylidene]amino}biphenyl (L2) were synthesized from the appropriate amine and aldehyde. Their co-ordination behaviour towards PdII, PtII and NiII has been studied. Dinuclear complexes were formed when treating L1 with 2 equivalents of [PdCl(Me)(cod)] (cod = cycloocta-1,5-diene) and Pd(O2CMe)2. In the case of the reaction of L1 with Pd(O2CMe)2 an unexpected double cyclopalladated complex was formed. However, treatment of L1 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 [Pd2L1Cl2Me2] 1 has been established by an X-ray diffraction study. The dihedral angle between the biphenyl rings is 49.2(8)° and the intramolecular Pd· · ·Pd distance is 7.165(3) A. The biphenyl bridging moiety shows a remarkable bending of 169.2(8)°. Treatment of 1 with carbon monoxide resulted in a double CO insertion, yielding the bis(acetyl)palladium compound [Pd2L1Cl2{C(O)Me}2] 2. The structure of [Pd2L1(O2CMe)2]·4CH2Cl2 3 was also determined by X-ray diffraction. The dihedral angle between the biphenyl rings is 75.9(14)° while the intramolecular Pd· · ·Pd distance is 8.655(2) A. The reaction of L2 with 2 equivalents of anhydrous [PdCl2(MeCN)2] or NiCl2 afforded mononuclear complexes. The crystal and molecular structure of [PdL2]Cl2·3.5CH2Cl2 was determined. The compound has an approximately square-planar P2N2 geometry.