Synthesis, characterization and reactivity of mono-,di-and tripalladated ortho-substituted arenes = Síntesis, caracterización y reactividad de arenos mono-, di- y tripaladiados con sustituyentes en orto

Resumo

SYNTHESIS, CHARACTERIZATION AND REACTIVITY OF MONO-, DI-, AND TRIPALLADATED ORTHO-SUBSTITUTED ARENES 1. OBJECTIVES This Thesis follows a research line focused on the synthesis of ortho-substituted arylpalladium(II) complexes and the investigation of their reactivity towards unsaturated molecules. These reactions often result in the insertion of these molecules into the aryl-Pd bond, sometimes followed by their interaction with the substituent in ortho position, forming new complexes (often cyclopalladated) or, after depalladation reactions, interesting organic molecules. Our research group is trying to extend this reactivity to di- or tripalladated arenes, with substituents in ortho position to each Pd atom, with the aim of obtaining new polynuclear complexes or polycyclic organic compounds. According to these antecedents, we aimed at the following goals: 1. Investigate the possibility of preparing new mono-, di-, or tripalladated arenes with R substituents in ortho position, with special emphasis on compounds with R = CH2OH, which had not been investigated before. Their reactivity would be compared with that of related complexes with R = OH 2. Prepare dinuclear Pd(II) complexes with a 2,5-distyrylbencene ligand and investigate their reactivity toward alkynes, with the aim of obtaining dinuclear indacenediyl complexes. Investigate also their reactivity towards other unsaturated molecules, such as isocyanides. 3. Prepare dinuclear Pd(II) complexes derived from terephthalaldehyde and investigate their reactivity toward unsaturated molecules. 2. METHODOLOGY ortho-Substituted mono-, di-, or tripalladated arenes were prepared by oxidative addition of aryl mono-, di-, or trihalides to [Pd(dba)2] in the presence of auxiliary ligands, such as bpy, tbbpy, tmeda, or phosphines. In the reactions with trihalides the influence of the arene, the auxiliary ligands, and the reaction conditions on the number of Pd atoms coordinated to the arene was investigated. The reactivity of the new complexes towards unsaturated organic molecules, such as alkynes, isocyanides, carbon monoxide or carbodiimides was investigated, resulting in the formation of new complexes, usually derived from the insertion of these molecules into the aryl-Pd bonds. In a few occasions, depalladation reactions took place, resulting in interesting organic compounds. The new products were characterized by IR and NMR spectroscopy, as well as by elemental analysis or mass spectroscopy. X-ray diffraction studies were conducted on some of them. 3. RESULTS 1) New mononuclear arylpalladium(II) complexes derived from benzyl alcohol have been prepared, and their reactivity towards unsaturated organic molecules has been investigated, resulting in new complexes derived from insertion reactions into the aryl-Pd or O-Pd bond (the latter in a cyclopalladated derivative, which also reacts as a nucleophile towards aryl halides). The presence of Ag+ is a requirement in some of these insertion reactions, and a heterometallic Pd2Ag derivative has been obtained as well. 2) New mono- and dinuclear Pd(II) complexes with a 2,5-distyrylbenzene ligand have been prepared, and their reactivity towards alkynes and isocyanides has been investigated, resulting in new dinuclear complexes, among them some novel indacenediyl Pd(II) complexes. 3) Dinuclear Pd(II) complexes derived from terephthalaldehyde have been prepared, and in their reactions with carbon monoxide and xylylisocyanide, the insertion of these molecules into two aryl-Pd bonds on the same aryl ring has been achieved for the first time. 4) New trinuclear arylpalladium(II) complexes have been prepared, and the insertion of xylylisocyanide into three aryl-Pd bonds on the same aryl ring has been achieved. 5) During a 3-month research stay at the University of Lisbon the synthesis and reactivity of new Pd(II) bis(tetrazolato) complexes was investigated.