Synthesis and characterization of aluminum complexes of 2-pyrazol-1-yl-ethenolate ligands

Abstract

The synthesis and the characterization of some new aluminum complexes with bidentate 2-pyrazol-1-yl-ethenolate ligands are described. 2-(3,5-Disubstituted pyrazol-1-yl)-1-phenylethanones, 1-PhC(O)CH 2-3,5-R 2C 3HN 2 ( 1a, R = Me; 1b, R = Bu t ), were prepared by solventless reaction of 3,5-dimethyl pyrazole or 3,5-di- tert-butyl pyrazole with PhC(O)CH 2Br. Reaction of 1a or 1b with AlR 3 1 (R 1 = Me, Et) yielded N, O-chelate alkylaluminum complexes [ R 2 1 AlOC ( Ph ) CH { ( 3 , 5 - R 2 C 3 HN 2 ) - 1 } ] ( 2a, R = R 1 = Me; 2b, R = Bu t , R 1 = Me; 2c, R = Me, R 1 = Et). Compound 1a was readily lithiated with LiBu n in thf or toluene to give lithiated species 3. Treatment of 3 with 0.5 equiv of MeAlCl 2 or AlCl 3 yielded five-coordinated aluminum complexes [XAl(OC(Ph)CH{(3,5-Me 2C 3HN 2)-1}) 2] ( 4, X = Me; 5, X = Cl). Reaction of 5 with an equiv of LiHBEt 3 generated [Al(OC(Ph)CH{(3,5-Me 2C 3HN 2)-1}) 3] ( 6). Complex 6 was also obtained by reaction of 3 with 1/3 equiv of AlCl 3. Treatment of 5 with 2 equiv of AlMe 3 yielded complex 2a, whereas with an equiv of AlMe 3 afforded a mixture of 2a and [Me(Cl)AlOC(Ph)CH{(3,5-Me 2C 3HN 2)-1}] ( 7). Compounds 1a, 1b, 2a– 2c and 4– 6 were characterized by elemental analyses, NMR and IR (for 1a and 1b) spectroscopy. The structures of complexes 2a and 5 were determined by single crystal X-ray diffraction techniques. Both 2a and 5 are monomeric in the solid state. The coordination geometries of the aluminum atoms are a distorted tetrahedron for 2a or a distorted trigonal bipyramid for 5.