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.