Studies on the coordination chemistry of methylated xanthines and their imidazolium salts. Part 1: Benzyl derivatives


Abstract:

New imidazolium salts derived from the natural methylated xanthines theophylline, theobromine and caffeine, namely 1,3-dimethyl-9-benzylxanthinium bromide (tphBzBr, 1a), 3,7-dimethyl-9-benzylxanthinium bromide (tbrBzBr, 2a) and 1,3,7-trimethyl-9-benzylxanthinium bromide (caffBzBr, 3a), are reported. Also, the disubsti- tuted analog of 1a, 1,3-dimethyl-7,9-dibenzylxanthinium bromide (tphBz2Br, 1a′) was identified and characterized by NMR. The coordination chemistry of ligands 1a-3a toward palladium, and some theoretical aspects of the unmodified theophylline, theobromine and caffeine are studied. Our results prove that the theophylline derivative has the thermodynamic tendency to form N-bonded species, even when an equilibrium between the Pd-NHC and the "theophyllinate" was observed spectroscopically, due to the anisotropy of the NHC ligand. To confirm the N- coordination, the solid state structure of the new "theophyllinate" species PdBr2(tphBz- H)2 (4), derived from 1a, was determined by X-ray diffraction. The analog with theobromine, ligand 2a, coordinates to palladium via N1, in an analogous manner to 1a, and a mixture of the cis/trans isomers of its palladium complex is obtained. On the other hand, since there is no possibility of N-coordination in 3a, this caffeine derivative forms a Pd-NHC compound after deprotonation with a strong base. Both the theoretical results and the experimental evidence are in accordance, in terms of the pbkp_redicted coordination sites or possibility of modification of the selected methylated xanthines to obtain new ligands. © Springer Science+Business Media B.V. 2009.

Año de publicación:

2010

Keywords:

    Fuente:

    scopusscopus

    Tipo de documento:

    Article

    Estado:

    Acceso restringido

    Áreas de conocimiento:

    • Química inorgánica
    • Química general
    • Bioquímica

    Áreas temáticas:

    • Química orgánica