Funcionalización catalítica de metano y alcanos ligeros con complejos metálicos del grupo 11

Abstract

The main objectives in this Ph. D. Thesis are focused in the development of catalytic systems toward the functionalization of highly inert molecules such as gaseous alkanes (CnH2n+-2, n = 1-4). The reaction employed toward that end is the metal-catalyzed carbene (CHCCbEt) transfer reaction from ethyl diazoacetate (N2=CHC02Et, EDA): The results have been classified in three Sections, describing novel catalytic systems for methane and light alkanes (ethane, propane, butane) catalytic functionalization. Section 1: New catalysts for methane and light alkane functionalization A new ligand of the hydrotris(pyrazolyl)borate (Tpx) family has been synthetized, the hydrotris((3,5- bis (triflu oro me thyl) - 4 -br o mo) -pyr a zo lyl)b or ate (TpiCF3:,2>Br). Its thalium, copper and silver complexes TlTpÍCF3E>Br (1) TpCCF3E>BrCu(NCMe) (2) and Tp(CF3}2,BrAg(thf) (3) have been prepared and fully characterized, including X-ray studies for their solid state structure. Complexes 2 and 3 display catalytic activity for the reaction of EDA and methane or other gaseous alkanes in supercritical carbon dioxide as the reaction medium. This is the first example of a soluble copper-based methane functionalization reaction. In the reactions carried out employing complex 2 as catalyst, an increase of the regioselectívity toward the primary sites has been observed when scCOi is used as the reaction medium, comparing the results with those experiments performed in neat (liquid) alkanes. This “supercritical effect11 seems to be related to an interaction of the supercritical medium with the catalyst through the fluorine atoms, which decrease the electron density at the metal center. Section 2: Studies of the relative reactivity of alkanes toward metailocarbenes. The relative reactivity (Rr) of a series of fourteen alkanes (CnH2n+2, n = 1-8) and twenty-nine different carbon- hydrogen bonds has been determined upon performing competition experiments both in scCCh and/or neat alkanes as the reaction media. Several silver-based catalysts have been used as the electrophile (metallocarbene) precursor, and the relative reactivity has been referenced to that of the methane carbon-hydrogen bond. Experimental data have been analyzed from a statistic point of view, from which a simple model has been built. Such model consists of an equation an a series of very simple rales that, based on topological descriptors of each C-H bond, leads to an estimated value of each relative reactivity that fits quite accurately with the experimental data. The model is not only applicable to the silver catalysts but also to others based on rhodium or copper. Section 3: Methane catalytic functionalization in water at room temperature A catalytic system for the reaction of methane (or other gaseous alkanes) with EDA in the presence of 3 as the catalysts that operates in water at room temperature has been developed. To achieve such outcome, a surfactant is required to generate micelles that concentrate catalyst and reactants in the inner hydrophobic cavity. Sodium docedyl sulphate has been found as the most appropriate surfactant for such purpose. With this strategy, methane has been converted into ethyl propionate with a 8% yield (EDA-based), whereas the remaining diazo reagent seems to be incorporated to the hydrophobic chains of the surfactant.