Aryl-extended calix[4]pyrrole receptors with metal centers: organometallic receptors and metallo-macrocycles based on coordination bonds

Identifier:  TDX:4310

Handle: https://hdl.handle.net/20.500.11797/TDX4310

Authors:  Rivoli, Andrea

Abstract:
This thesis focuses on the design and synthesis of unprecedent organometallic calix[4]pyrroles. 11 also deals with the study of the impact of the organometallic moieties on the binding properties of the prepared receptors. We used the scaffolds of a,a- anda, - 'two wall' aryl-extended calix[4]pyrrole isomers to incorporate metallo-ethynyl (metal­ acetylide) units al the para-positions of their meso-phenyl substituents. We studied the receptors' binding properties using 1H NMR titration experiments with tetraalkylammonium chloride salts and pyridine N-oxide derivatives as guest. A non-symmetric a,a--'two-wall' mono-ethynyl-Au(I) calix[4]pyrrole showed a decrease in binding affinity toward tetraalkylammonium chloride salts compared to its synthetic precursors. We also showed that a symmetric a,a-'two­ wall' calix[4]pyrrole with p-ethynyl-Pt(II) substituents self-assemble into metallo-macrocycles by coordination with strap ligands (i.e. di(pyridinyl)pyridine-2,6-dicarboxamide). We quantified the stability of the 1:1 complexes formed by a metallo-macrocycle and its non-cyclic precursors with N-oxide derivatives. Pyridine-N-oxide was similarly bound by the cyclic and non-cyclic receptors. Conversely, bis-pyridine-4,4'-di-N-oxide was only bound to the non-cyclic precursors. The 1:1 chloride complex of a non-symmetric a, ·'two-wall calix[4]pyrrole receptor bearing one p-acetylide-Au(I) substituent adopted two different conformations. We undertook VT 1H-NMR experiments to determine the composition of the equilibrium involving the two possible conformers, as well as of its synthetic precursors. The chloride complex