Neutral and Ionic Aluminum, Gallium, and Indium Compounds Carrying Two or Three Terminal Ethynyl Groups^†

The syntheses of the ionic compounds [Li+·2 dioxane (2,6-iPr2C6H3N(SiMe3)Al(C⋮CSiMe3)3)-]·0.75 dioxane (1), [(Li+)2·(dioxane)7]0.5 [2,6-iPr2C6H3N(SiMe3)Ga(C⋮CSiMe3)3-]·1.5 dioxane (2), and [(Li+)2·(dioxane)7]0.5 [2,6-iPr2C6H3N(SiMe3)In(C⋮CSiMe3)3-]·1.5 dioxane (3) by the reaction of the corresponding organo metal chloride with LiC⋮CSiMe3 are reported. The neutral ethynyl compounds Br−Al(C⋮CtBu)2·2 THF (4), Cl−Ga(C⋮CtBu)2·THF (5), Cl−In(C⋮CtBu)2·2 THF (6), Al(C⋮CtBu)3·C{N(Me)CMe}2 (7), Ga(C⋮CtBu)3·dioxane (8), and In(C⋮CtBu)3·NEt3 (9) have been obtained in good yields from the reaction of AlBr3, GaCl3, and InCl3 with LiC⋮CtBu in the presence of a Lewis base. Compound 7 is the first heterocyclic carbene substituted ethynyl derivative. Aluminum and gallium compounds with three terminal ethynyl groups Al(C⋮CPh)3·NMe3 (10) and Ga(C⋮CPh)3·NMe3 (11) have been prepared by the reaction of AlH3·NMe3 or GaH3·NMe3 with three equivalents of phenylethyne. All the above-mentioned compounds have been structurally studied. In compound 1 the lithium ion is coordinated to the three terminal ethynyl groups, whereas in compounds 2 and 3 the lithium is coordinated to the solvent (dioxane). Compound 8 crystallizes as a coordination polymer with dioxane molecules bridging the individual gallium units.