New palladium, platinum and nickel complexes based on rigid phosphorus and nitrogen containing ligands

Article abstract of DOI:10.1016/s0020-1693(97)05605-3

Three new polydentate phosphorus nitrogen ligands, 1,3-bis[N,N′-(2-diphenylphosphino)phenylformimidoyl]benzene (3), bis[N,N′-(2-diphenylphosphino)phenyl]-1,3-benzenedicarboxamide (6) and bis[N,N′-(2-diphenylphosphino)phenyl]-2,6-pyridinedicarboxamide (7) with rigid bridging groups have been synthesised. Ligand 7 shows an unexpected large non-bonding P-P coupling of 34 Hz, which can be attributed to the interaction of the lone pairs of the two phosphorus atoms which are directed towards each other due to hydrogen bonding between the two amide hydrogens and the pyridine nitrogen. Complexation experiments with these ligands showed that 3 is a good dinucleating ligand which resulted in the isolation of dichlorodimethyl{1,3-bis[N.N′-(2-diphenyl)phosphinophenylformimidoyl] benzene}dipalladium (8). In contrast only mononuclear palladium, platinum and nickel complexes have been obtained from ligand 7. The crystal and molecular structure of dichloro{bis[N,N′-(2-diphenylphosphino)phenyl]-2,6-pyridinedicarboxamide} platinum (9) was determined by X-ray crystallography. Complex 9 crystallises in the monoclinic space group C2/c with a=35.547(3), b=9.192(1), c=24.192(2) ?, β=102.795(7)°, V=7925.3(13) ?³ and Z=8; the structure was refined to R_F=0.031. This complex has a square planar configuration around platinum, in which the two phosphorus atoms are positioned trans to each other. For comparison, mononuclear complex dichlorobis(2-diphenylphosphinoaniline)platinum (12) was prepared and the structure elucidated by X-ray analysis. Complex 12 crystallises in a triclinic space group P1? with a=10.0692(12), b=10.839(2), c=24.350(5) ?, α=88.042(15), β=79.091(14), γ=75.518(11)°, V=2526.4(8) ?³ and Z=2; the structure was refined to R_F=0.0355. In platinum complex 12, a square planar geometry is found but the two phosphines are positioned cis to each other, whereas an unusual binding of the chloride anions is observed.