ABSTRACT
Heterochiral self-sorting into only one stereoisomer is observed when metallo-supramolecular squares self-assemble from amino acid-substituted, dynamically interconverting bipyridine stereoisomers and dpppM(OTf)(2) corners (M = Pd, Pt).
Subject(s)
Amino Acids/chemistry , Organometallic Compounds/chemical synthesis , Pyridines/chemistry , Ligands , Magnetic Resonance Spectroscopy/methods , Magnetic Resonance Spectroscopy/standards , Molecular Conformation , Organometallic Compounds/chemistry , Palladium/chemistry , Platinum/chemistry , Reference Standards , StereoisomerismABSTRACT
It is found that 4,4'-bipyridines functionalized in their 3,3'-positions with Fréchet dendrons of 0th to 3rd generation self-assemble with (dppp)M(II) triflates (dppp: bis-(diphenylphosphino)propane; M = Pd, Pt) into metallo-supramolecular squares. They bear a nanometer-sized cavity inside an unpolar dendritic shell. A total of eight amide groups decorate the rims of the cavity connecting the dendrons to the square. Evidence for their formation up to the third generation comes from ESI-FTICR mass spectrometry and NMR experiments. Based on these results, the presence of significant amounts of other polygons or open-chain oligomers can be excluded. Exchange processes have been studied by variable-temperature NMR spectroscopy and by following the ligand exchanges between different squares by mass spectrometry. The ligand exchange is much slower for the Pt(II) squares as compared to their Pd(II) analogs. Visualization of films of these dendrimers using atomic force microscopy (AFM) provides information on their molecular dimensions. After deposition of a square monolayer on the surface, a slow reorganization within this layer is observed which leads to the formation of "tower-like" aggregates and multi-layer formation. The interplay of interactions between the dendrimers and the surface and interactions between different dendrimers are invoked to rationalize the observations.
Subject(s)
Air , Dendrimers/chemistry , Gases/chemistry , Metals/chemistry , 2,2'-Dipyridyl/chemistry , Aluminum Silicates/chemistry , Ligands , Magnetic Resonance Spectroscopy , Microscopy, Atomic Force , Propranolol/chemistry , Solutions , Spectrometry, Mass, Electrospray Ionization , TemperatureABSTRACT
The self-assembly reactions between the fluorinated ditopic ligand 1,4-bis(4-pyridyl)tetrafluorobenzene (A) and different nitrogen-protected palladium(II) and platinum(II) complexes have been investigated. While dynamic equilibria between molecular triangles and squares were observed when the diimine compounds 4,4'-R2bipy (bipy = 2,2'-bipyridine; R = H, Me, t-Bu) were employed as ancillary ligands, only square species were obtained from ethylenediamine (en) derivatives. Characterization of the obtained metallomacrocycles was accomplished by 1H and 19F NMR spectroscopy in combination with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR). Molecular dynamics simulations (UFF) have been performed to interpret the influence of the fluorinated ring on the square/triangle relative stability. Density functional calculations using the GIAO method have been employed for the interpretation of the chemical shift assignments. The study of the ability of these compounds to act as hosts of electron-rich aromatic guests has shown that the palladium ethylenediamine square is capable of establishing this type of intermolecular interaction exclusively in aqueous media. The host-guest stoichiometry and association constants have been determinated by 1H NMR spectroscopy.
