Details

Síntesi d'àcids carboxílics d'alt valor afegit via hidrocarboxilació catalítica amb nous complexos de pal·ladi de baixa simetria. Deuteriocarboxilació com a eina d'obtenció d'informació mecanística

by Pagès Barenys, Montserrat

Abstract (Summary)
In this work we have shown that, mediating the oxidative addition reaction of tetrakistriphenylphosphine paladium(0), it is possible to obtain chlorothiolcomplexes using the hydrochlorides cysteamine, L-cysteine ethyl ester and D-pencillamine methyl ester, and one triphenylphosphine which proceeds from the tetrakistriphenylphosphine paladium(0). If the reactant used is Pd(dba)2 and we added 1 equivalent of PMePh2, we obtain the chlorothiolcomplexe with one molecule of L-cysteine ethyl ester and one molecule of methyldiphenylphosphine as ligands. These new isolated complexes are mononuclear and have low symmetry. Some of them only have a symmetry plain that contains the molecule and, in other cases, this plain is broken by a more bulky ligand that produces asymmetric complexes C1. The structures 1-6 have been characterised by IR and NMR (1H, 13C and 31P{1H}). In addition, in the case of 1 and 2 it has been possible to obtain their crystalline structure by X-ray diffraction methods where we have confirmed their squareplane structure and the position trans of anionic ligands. The hydrocarboxylation catalytic experiments we have done shown that the catalytic systems, which we have developed in this work, A and B are actives and gives a very good regioselectivity in the synthesis of 2-arilpropionic acids (2-phenylpropionic, 2-(4-tert-butylphenyl)propionic, 2-naphtalen-2-il-propionic) and acenaphthene-1-carboxylic acid, otherwise they are inactives in the hydrocarboxylació of trans-anethol and trans-1,2-dimetoxy-4-(1-propenyl)benzene. On the other hand, the catalytic systems C, D and D' have a high activity and are extremely selectives in the synthesis of the acids 2-(4-metoxyphenyl)butyric and 2-(3,4-dimetoxyphenyl)butyric. In this evaluation it has been possible to observe that the use of complexes 1 and 2 as catalytic precursors decreases activity but produces a great increase in the production of the branched acid. However, there is no enantioselectivity in this process although complex 2 is a quiral precursor. In this way, we thought that the cysteinic ligand, in the reaction conditions, acts in a monocoordinated manner trough the thiol group, which produces that the asymmetric centre was so far away from the metallic nucleus. Through deuteriocarboxylation experiments it has been possible to obtain some mechanistic conclusions about this reaction. We thought that, from the obtained results and with the used catalytic systems, the catalytic reaction goes through an hydride mechanism. In addition, the results show that the insertion of the carboxylate group and the hydrogen atom in the carbon b happens in cis and we have evaluated in each case how important is the collateral elimination-b. process. Moreover, we have observed, apparently for the first time, an inversion process on the alquilic intermediate through a nucleofilic atac by Pd(0).
This document abstract is also available in Catalan.
Bibliographical Information:

Advisor:Juli Real Obradors

School:Universitat Autónoma de Barcelona

School Location:Spain

Source Type:Master's Thesis

Keywords:403 departament de quimica

ISBN:

Date of Publication:07/06/2001

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