Noncovalent Assembly and Catalytic Activity of Hybrid Materials Based on Pd Complexes Adsorbed on Multiwalled Carbon Nanotubes, Graphene, and Graphene Nanoplatelets.

Green catalysts with excellent performance in Cu-free Sonogashira coupling reactions can be prepared by the supramolecular decoration of graphene surfaces with Pd(II) complexes. Here we report the synthesis, characterization, and catalytic properties of new catalysts obtained by the surface decoration of multiwalled carbon nanotubes (MWCNTs), graphene (G), and graphene nanoplatelets (GNPTs) with Pd(II) complexes of tetraaza-macrocyclic ligands bearing one or two anchor functionalities. The decoration of these carbon surfaces takes place under environmentally friendly conditions (water, room temperature, aerobic) in two steps: (i) π-π stacking attachment of the ligand via electron-poor anchor group 6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxo-pyrimidine and (ii) Pd(II) coordination from PdCl.

Non-covalent Functionalization of Graphene to Tune Its Band Gap and Stabilize Metal Nanoparticles on Its Surface.

Controlling graphene conductivity is crucial for its potential applications. With this focus, this paper shows the effect of the non-covalent bonding of a pyrimidine derivative (HIS) on the electronic properties of graphene (G). Several G-HIS hybrids are prepared through mild treatments keeping unaltered the structures of both G and HIS.

A New Heterogeneous Catalyst Obtained via Supramolecular Decoration of Graphene with a Pd Azamacrocyclic Complex.

A new G-(HL)-Pd heterogeneous catalyst has been prepared via a self-assembly process consisting in the spontaneous adsorption, in water at room temperature, of a macrocyclic HL ligand on graphene (G) (G + HL = G-(HL)), followed by decoration of the macrocycle with Pd ions (G-(HL) + Pd = G-(HL)-Pd) under the same mild conditions. This supramolecular approach is a sustainable (green) procedure that preserves the special characteristics of graphene and furnishes an efficient catalyst for the Cu-free Sonogashira cross coupling reaction between iodobenzene and phenylacetylene. Indeed, G-(HL)-Pd shows an excellent conversion (90%) of reactants into diphenylacetylene under mild conditions (50 °C, water, aerobic atmosphere, 14 h).

Polyfunctional Tetraaza-Macrocyclic Ligands: Zn(II), Cu(II) Binding and Formation of Hybrid Materials with Multiwalled Carbon Nanotubes.

The binding properties of HL1, HL2, and HL3 ligands toward Cu(II) and Zn(II) ions, constituted by tetraaza-macrocyclic rings decorated with pyrimidine pendants, were investigated by means of potentiometric and UV spectrophotometric measurements in aqueous solution, with the objective of using the related HL-M(II) (HL = HL1-HL3; M = Cu, Zn) complexes for the preparation of hybrid MWCNT-HL-M(II) materials based on multiwalled carbon nanotubes (MWCNTs), through an environmentally friendly noncovalent procedure. As shown by the crystal structure of [Cu(HL1)](ClO), metal coordination takes place in the macrocyclic ring, whereas the pyrimidine residue remains available for attachment onto the surface of the MWCNTs via π-π stacking interactions. On the basis of equilibrium data showing the formation of highly stable Cu(II) complexes, the MWCNT-HL1-Cu(II) material was prepared and characterized.

Thermodynamics of anion-π interactions in aqueous solution.

Thermodynamic parameters (ΔG°, ΔH°, TΔS°), obtained by means of potentiometric and isothermal titration calorimetry (ITC) methods, for the binding equilibria involving anions of high negative charge, like SO(4)(2-), SeO(4)(2-), S(2)O(3)(2-) and Co(CN)(6)(3-), and nitroso-amino-pyrimidine receptors in water suggested that anion-π interactions furnish a stabilization of about -10 kJ/mol to the free energy of association. These anion-π interactions are almost athermic and favored by large entropic contributions which are likely due to the reduced hydrophobic pyrimidine surface exposed to water after anion aggregation, and the consequent reduced disruptive effect on the dynamic water structure. The crystal structure of the {H(4)L[Co(CN)(6)]}·2H(2)O complex showed strong anion-π interactions between Co(CN)(6)(3-) and the protonated H(4)L(3+) receptor.