Reaction of 1,3-diols with Al(tBu)3 and Ga(tBu)3: aluminium- and gallium-based bifunctional tetradentate ligands

Abstract

Reaction of M(tBu)3 (M = Al, Ga) with neol-H2 (2,2-dimethylpropane-1,3-diol) yields [M2(tBu)4(neol-H)2], M = Al (1) and Ga (2), respectively. Use of an equimolar mixture of Al(tBu)3 and Ga(tBu)3 allows for the formation of [AlGa(tBu)4(neol-H)2] (3). Compounds 1 and 2 may be considered as bifunctional (two OH groups), tetradentate (4O) ligands as highlighted by their reactivity with Group 13 hydrides and alkyls. Reaction of compound 1 with AlH3(NMe3), AlH2Cl(NMe3) and AlMe3 yields the tri-aluminium compounds, [Al3(tBu)4(X)(neol)2] with X = H (4), X = Cl (5), Me (6), respectively. Similarly, compound 2 reacts with Ga(tBu)3 to yield the tri-gallium compound, [Ga3(tBu)5(neol)2] (7). The mixed metal complexes, [Ga2Al(tBu)4(X)(neol)2], where X = H (8), Me (9) and tBu (10), are formed by the reaction of compound 2 with AlH3(NMe3), AlMe3, and Al(tBu)3, respectively. The solid state conformation of the neol backbone and the 1H NMR chemical shift of the neol's CH2 protons, in compounds 4–10, are both dependent on the steric bulk of the substituent of the central metal. Thermolysis of compound 2 in toluene results in the formation of [Ga3(tBu)4(CH2Ph)(neol)2] (11), while the reaction of 2 with LiOH in Et2O and hexane yields [Ga3Li4(tBu)6(neol)3(OH)(THF)] (12) and [Ga2Li(tBu)4(OH)2(neol-H)] (13), respectively. The molecular structures of compounds 1, 2, 4–13 and [Ga3Cl5(OSiMe2OSiMe2O)2] (14) have been determined by X-ray crystallography.