Compuestos moleculares y supramoleculares de metales de transición con potenciales aplicaciones

Abstract

In this Thesis new molecular and supramolecular species of Pd (II) and Pt (II) have been prepared: on the one hand, we synthesized Pt (II) complexes derived from hydrazone ligands, and on the other hand, we prepared rectangular metallacycles derived of N-monoalkyl-4,4'-bipyridinium and Pd (II) and Pt (II) metal centres, containing in their structure the carbene 1,1'-di (methyl) -3,3 methylene-4-diimidazole- 2,2'-ylidene. We observed that the reactivity of the N-phenylhydrazones a-d (a= 2-Cl-C6H4N(H)N=CMe(C5H4N); b= 3-Cl-C6H4N(H)N=CMe(C5H4N); c= 2,4-Cl-C6H3N(H)N=CMe(C5H4N); d= C6H5N(H)N=CMe(C5H4N)) versus K2PtCl4 in n-butanol/water at 100 °C depends on the substitution of the phenyl ring. Thus, when the hydrazones a and d reacted the mononuclear coordination complexes 1a and 1d are obtained, with the hydrazone ligands acting as bidentates [N, N] chelate. However, the reaction of the hydrazones c and d with K2PtCl4, under analogous reaction conditions, leads directly to the formation of the cyclometallated species 2b and 2c. When the coordination compounds 1a and 1d are treated with sodium acetate in n-butanol at 100 °C, the cyclometallated compounds 2a and 2d were obtained after activation of the C-H bond. DFT calculations were carried out in an attempt to understand the different reactivity of the ligands, studying the possible mechanism of the reaction of these ligands with K2PtCl4, which suggests that the formation of the cyclometallated species takes place through a mechanism of the aromatic electrophilic substitution, so that the substitution in the phenolic ring greatly affects to the reactivity of the C-H bond for the formation of the corresponding cyclometallated compound. On the other hand, it was determined that the presence of acetate in the reaction medium favours the deprotonation of N-H and facilitates electrophilic activation of the C-H bond. Although calculations determine that the most stable species are the coordination complexes, the formation of cyclometallates can be justified by the solvation energy of the HCl in the solvent or the neutralization with the base, which shifts the equilibrium towards the formation of the cyclometallated species. The ligand hydrazone e (3,4-Me2- C6H2C(Me)=NN(H)(4’-Cl-C4H2N2)) undergoes the same reaction and leads the cyclometallated specie 1e, which was carried out a study of its reactivity to different tertiary phosphines, leading to the production of new mononuclear and trinuclear complexes. The crystal structure obtained by X-ray diffraction of two of these complexes, shows interesting p-p interactions between chelate rings and aromatic rings. It was possible to obtain M2L2 dinuclear metallocyclic receptors, with square and rectangular shape, in water from ligands derived of N-monoalkyl-4,4'-bipyridinium and metal centers of Pd (II) and Pt (II), which contain in their structure a chelate carbene ligand. After the preparation of the metallocycles, the ability of these metal corners to perform the exchange of pyridine ligands was studied and on the other hand, a conformational study of this carbenes was carried out, through the formation of complexes with 2,2'-pyridine and 2,2'-bipyrimidine ligands and their modelling by DFT calculations. Due to the strong trans effect exerted by the carbene ligands, the synthesis of the Pt2L2 receptors was achieved as well by self-assembly of the components at room temperature in few hours, in clear contraposition to the harsh reaction conditions usually required for the labialization of other kinetically inert Pt(II)-N(pyridine) bonds. X-ray diffraction studies of suitable single crystals of two of the obtained receptors offered additional information on the structure of the obtained supramolecules, which ability as receptors has been explored by the preparation of the corresponding inclusion complexes in water with 1,5- dihydroxinaphthalene as model substrate.