Treatment of aminoalkynes (ynamines), Me3Si-CC-NR2 [NR2 = N(CH2CH2)2NMe, N(CHMe-CH2)2CH2], with dialkylaluminum hydrides, H-AlR′2 (R′ = CH2 tBu, iBu, tBu), afforded by hydroalumination the corresponding alkenyl derivatives R′2Al-(Me3Si)CC(H)-NR2 (3 to 6) in which the opposite Lewis functionalities adopted a cis-arrangement with the aluminum and nitrogen atoms on the same side of the resulting CC double bonds. Intramolecular Al–N interactions gave four-membered AlC2N heterocycles, but ring strain may cause relatively long Al–N distances of 2.07 to 2.15 Å. These compounds represent a new type of Lewis acid–base pairs, and we observed C–H bond activation by opening of the Al–N bond upon treatment with H-CC-C6H5. Compound 7 was isolated, which had the proton attached to nitrogen and the anionic ethynyl group bonded to aluminum. The formation of 7 is reversible in solution with an increasing dissociation into the starting compounds at elevated temperatures. Two different structural motifs were obtained upon reaction of the Lewis acid–base pairs with dicyclohexylcarbodiimide, which inserted selectively into the bond between the aluminum and the vinylic carbon atom. In the first compound (8) an amidinato ligand was formed, which coordinated the metal atom by both nitrogen atoms to give an AlCN2 heterocycle. A six-membered heterocycle (9) resulted from the insertion of only one CN double bond of the carbodiimide into the Al–C(vinyl) bond. 9 had an unchanged interaction of the metal atom with the α-nitrogen atom of the former ynamine. The latter compound may be considered an intermediate, and rearrangement to yield an amidinato compound analogous to 8 was indeed observed with extended reaction time.

Hydroalumination of cyanamides 1 with di(isobutyl)aluminium hydride affords intermediate compounds 3, which have dimeric structures in the solid state with four‐membered Al2N2 heterocycles and exocyclic N=C double bonds. The reactions of 3 with acyl chlorides yield N′,N′‐disubstituted N‐acylformamidines 5, whereas reaction with sulfonyl chlorides give the corresponding N‐sulfonylformamidines 7. In contrast, carbodiimides 8 react with dialkylaluminium hydrides R2AlH (R = tBu, iBu) to give compounds 9 in which one C=N bond of the carbodiimide is reduced to form an amidinate ligand and a second molecule of the hydride is coordinated through an Al–N and an Al–H–Al bond. Treatment of 9 with acyl chlorides yields N,N′‐disubstituted N‐acylformamidines 10, whereas reaction with sulfonyl chlorides gives the corresponding N‐sulfonylformamidines 11.

Treatment of 1,2-bis(trimethylsilylethynyl)benzene with di-tert-butylaluminum and di-tert-butylgallium hydrides afforded the simple addition products 1,2-[(Me 3 Si)(R 2 E)CdC(H)] 2 C 6 H 4 (R = CMe 3 ; E = Al (1), Ga (2)), which could not be isolated in a pure crystalline form but have been characterized unambiguously by spectroscopic methods. Addition of the Lewis base ethyldimethylamine initiated condensation reactions which gave cage compounds (3 and 4) by the release of the corresponding tri-tert-butyl element derivatives. These cages contain two aluminum or gallium atoms which are bridged by three 1,2-bis(trimethylsilylethenyl)benzene spacers to form molecular capsules. The metal atoms are further coordinated by terminal amino groups. The amino ligands could not be removed from the dialuminum compound 4 without decomposition, but the ligand-free gallium compound 5 was obtained upon heating of 3 (E = Ga) to 80 °C under vacuum. Thermolysis of the aluminum compound 1 in boiling n-hexane gave a unique reaction by the release of tri-tert-butylaluminum and the formal elimination of trimethylsilylethyne (decarbalumination). The product 6 is dimeric in the solid state via Al-C-Al bridges and has a pentacyclic molecular structure.

The synthetic potential of hydroalumination reactions of cyanamides and carbodiimides is demonstrated. The transformations proceed via reactive organoaluminium intermediates (not shown) which are partially isolable as solids. Only one of the two possible isomers is isolated from the reaction of unsymmetrical carbodiimides such as (VIII). -(HELLMANN, J.; RHOTERT, I.; WESTENBERG, H.; FROEHLICH, R.; WIBBELING, B.; UHL, W.; WUERTHWEIN*, E.-U.; Eur. J. Org. Chem. 2013, 16, 3356-3368, http://dx.

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