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RESEARCH PRODUCT

New Carbaalanes − (AlMe)8(CCH2Me)5(C≡C−Me) and the THF Adduct (AlMe)8(CCH2Me)5H·2THF

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description

The hydroalumination of Me2Al−C≡C−Me with a large excess of Me2AlH afforded the arachno-carbaalane (AlMe)8(CCH2Me)5H (4) by the release of AlMe3. 4 is almost insoluble in noncoordinating solvents and could not be purified by recrystallization. On an attempt to recrystallize 4 from a THF solution, the adduct (AlMe)8(CCH2Me)5H·2THF (5) was isolated as the first stable ether adduct of a carbaalane. Crystal structure determination revealed a cube of eight aluminium atoms, five faces of which are bridged by C−CH2Me groups. The sixth face is µ2-bridged by a hydrogen atom, and two opposite aluminium atoms of this face are coordinated by one THF ligand each. When the excess of dimethylaluminium hydride was reduced and the starting compounds were employed in a 1:2.1 molar ratio, an incomplete hydroalumination reaction led to the formation of the carbaalane (AlMe)8(CCH2Me)5(µ-C≡C−Me) (6), in which the bridging hydrogen atom of 4 is replaced by an alkynido group. 27Al NMR spectroscopic data of all the characterized carbaalanes are reported and supplemented by 27Al NMR chemical shift calculations.