Intramolecularly Stabilized o-Carboranyl Aluminum Complexes: Synthesis, Characterization, and X-ray Structural Studies

The chelating aluminum complex [2-(Me2NCH2)C2B10H10]AlX2 (X = Br 3, CH3 4) was synthesized using 2-dimethylaminomethyl-o-carboranyl lithium (LiCab(N), 2) with aluminum tribromide (AlBr3) or dimethylaluminum bromide (Me2AlBr), resulting in a modest yield. Compound 4 was obtained by reacting compound 3 with methyllithium (CH3Li) in toluene. All compounds were characterized using infrared (IR) spectroscopy; H-1, B-11, C-13 nuclear magnetic resonance (NMR) spectroscopy; and X-ray crystallography. X-ray structural studies of Cab(N)AlBr(2) (3) and Cab(N)AlMe(2) (4) (Cab(N) = 2-dimethylaminomethyl-o-carboranyl) indicated that the aluminum atom was located at the center of a distorted tetrahedron. Crystal structures of Cab(N)AlBr(2) (3) [a = 8.9360(3) & ANGS;, b = 12.0358(9) & ANGS;, c = 14.7730(4) & ANGS;, & alpha; = & beta; = & gamma; = 90 & DEG;] and Cab(N)AlMe(2) (4) [a = 8.9551(3) & ANGS;, b = 11.9126(9) & ANGS;, c = 14.7711(4) & ANGS;, & alpha; = & beta; = & gamma; = 90 & DEG;] were obtained. The reactivity of aluminum complexes 3 and 4 with Lewis bases, such as H2O, pyridine, alkylamines, and arylamines, confirmed their rapid decomposition due to the strong Lewis acidity of aluminum metals.