Investigations on the Interaction of Dichloroaluminum Carboxylates with Lewis Bases and Water: an Efficient Road toward Oxo- and Hydroxoaluminum Carboxylate Complexes

A series of dichloroaluminum carboxylates [Cl2Al(O2CR)](2) (were R = Ph (1a), Bu-t (1b), CHCH2 (1c) and C11H23 (Id)) were prepared and extended investigations on their structure and reactivity toward various Lewis bases and H2O performed. Compounds [Cl2Al(O2CR)](2) and their adducts with Lewis bases show a large structural variety, featuring both molecular and ionic forms with different coordination numbers of the metal center and various coordination modes of the carboxylate ligand. Upon addition of a Lewis base of moderate strength the molecular form [Cl2Al(O2CR)](2) equilibrates with new ionic forms. In the presences of 4-methylpyridine the six-coordinate Lewis acid-base adducts [Cl2Al(lambda(2)-O2CR)(py-Me)(2)] [R = Ph (3a), Bu-t (3b)] with a chelating carboxylate ligand were formed. The reactions of la, 1b, and Id with 0.33 equiv of H2O in THF-toluene solution lead to oxo carboxylates [(Al3O)(O2CR)(6)(THF)(3)] [AlCl4] [where R = Ph (4a(THF)), Bu-t (4b(THF)), and C11H23 (4d(THF))] in high yield. The similar reaction of 1c in tetrahydrofuran (THF) afforded the chloro(hydroxo)aluminum acrylate [(ClAl)(2)(OH)-(O2CC2H3)(2) (THF)4][AlCl4] (5), while the hydrolysis of 1b in MeCN lead to the hydroxoaluminum carboxylate [Al-2(OH)((O2CBu)-Bu-t)(2)(MeCN)(6)][AlCl4)(3)] (6). All compounds were characterized by elemental analysis, H-1, Al-27 NMR, and IR spectroscopy, and the molecular structure of 1a, 3a, 3b, 4aTHF, 4bTHF, 4b(py-Me'),, 5, and 6 were determined by single-crystal X-ray diffraction. The study provides a platform for testing transformations of secondary building units in Al-Metal-Organic Frameworks toward H2O and neutral donor ligands.