Resumen de Hydrolysis of the trifluoromethyl group in triarylphosphines: scope of the reaction in the preparation of carboxylic-trifluoromethylated phosphines and their applications
The present thesis describes the preparation of a new family of carboxylic-trifluoromethylated phosphines. These ligands have been synthesised by applying the reaction of hydrolysis of the trifluoromethyl group in trifluoromethylated triarylphosphines using fuming sulfuric acid and boric acid. This reaction offers a new approach to obtain carboxylic phosphines by applying a relatively simple synthetic procedure.
The scope and the applicability of the reaction have been studied in a set of eight trifluoromethylated aryl-monophosphines, both homoleptic and heteroleptic, and two trifluoromethylated aryl-diphosphines.
In the homoleptic aryl-monophosphines, the rate of the reaction of hydrolysis of the trifluoromethyl was found to depend on the pattern of substitution with respect to the phosphorus atom, it being faster in meta-position than in para. The ortho-substituted phosphine showed much slower rates than the meta and para-compounds together with the formation of spirocyclic oxyphosphoranes. Slow rates were also observed in the reaction of hydrolysis in trfluoromethyl groups in 3,5-position with the resulting oxidation of the phosphine. The heteroleptic phosphines showed that the reaction rate was slower when increasing the number of trifluoromethyl groups in the phosphines. With this procedure, eight new carboxylic-trifluoromethylated phosphines were prepared, purified and fully characterised.
In contrast, no carboxylic phosphines could be prepared from the hydrolysis of the trifluoromethyls in the trifluoromethylated diphosphines. Difficulties were found in the protection of these phosphines which in contact with oleum yielded the corresponding phosphine oxides.
Moreover, the reaction of hydrolysis of the trifluoromethyl group was analysed in detail, including the study of the species involved in the reaction and their role as well as the mechanism of formation of the carboxylic acid from the trifluoromethyl group. In this context, the mechanism of formation of the spirocyclic oxyphosphoranes was proposed. The carboxylic-trifluoromethylated monophosphines were used in the preparation of chelating diphosphines by reaction with a diamine leading to amide linkages. Vinyl moiety was included in the structure of the diamine in order to eventually form a polymer-supported diphosphine by co-polymerisation with latex particles. The study of these ligands in the Rh-catalysed hydroformylation of 1-octene showed the chelating behaviour of the phosphines with regioselectivities up to 97 %, expressed as the percentage of linear aldehyde relative to total aldehydes obtained.
