Neutral molecular Pd6 hexagons using k3-P2O-terdentate ligands

The one-step synthesis of three new P2O-terdentate carboxylic acid ditertiary phosphines 2-{(Ph2PCH2)(2)N}-3-(X) C6H3CO2H (X = OCH3, L1; X = OH, L2) and 2-{(Ph2PCH2)(2)N}-5-(OH) C6H3CO2H (L-3) by a phosphorus-based Mannich condensation reaction using Ph2PCH2OH and the appropriate amine in CH3OH is reported. Compounds L1-L3 function as typical kappa(2)-P-2-didentate ligands upon complexation to Pd(CH3)Cl(cod) (cod = cycloocta-1,5-diene), affording the neutral, mononuclear complexes Pd(CH3)Cl(L1-L3) (1-3). Metathesis of 1 with NaX (X = Br, I) gave the corresponding (methyl) bromopalladium(II) (4) and (methyl) iodopalladium(II) (5) complexes, respectively. When chloroform or chloroform/methanol solutions of 1-3 (or 5) were allowed to stand, at ambient temperatures, yellow crystalline solids were isolated in very high yields (71-88%) and were analyzed for the novel hexameric palladium(II) compounds 6-9. All new compounds reported have been fully characterized by a combination of spectroscopic (multinuclear NMR, Fourier transform IR, electrospray mass spectrometry, matrix-assisted laser desorption ionization time-of-flight mass spectrometry) and analytical methods. The self- assembly reactions are remarkably clean as monitored by P-31{H-1} and H-1 NMR spectroscopy. Single-crystal X-ray structures have been determined for L1, 4, 7 center dot 17CDCl(3)center dot 2Et(2)O, 8 center dot 6CHCl(3)center dot 8CH(3)OH, and 9 center dot 17CDCl(3). In hexamers 7-9, all six square-planar palladium(II) metal centers comprise a kappa(2)-P-2-chelating diphosphine, a kappa(1)-O-monodentate carboxylate, and either a chloride or iodide ligand, leading to 48-membered metallomacrocycles (with outside diameters of ca. 2.5 nm). Whereas only intramolecular O-H center dot center dot center dot N hydrogen bonding between the hydroxy group and tertiary amine has been observed in 7, strong intermolecular O-H center dot center dot center dot O hydrogen bonding of the type CO center dot center dot center dot HO(CH3)center dot center dot center dot HO, involving a methanol solvate, has been found in 8, leading to an unprecedented three-dimensional network motif.