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 sterically highly shielded terminal alkynes, H-C≡C-aryl, with dialkylaluminium and dialkylgallium hydrides, R 2 E-H, afforded by hydrogen release dimeric dialkylelement alkynides with a four-membered E 2 C 2 heterocycle independent of the bulk of the aryl groups. A rare example of a monomeric alkynylaluminium compound was only obtained with very bulky CH(SiMe 3 ) 2 groups attached to the metal atoms and by salt elimination reaction. The steric shielding by the bulky aryl groups did not prevent condensation reactions. Hydroalumination of 1-(trimethylsilyl)-2-(2,6-dimethylphenyl)ethyne using Me 2 Al-H resulted in a divinyl compound by elimination of trimethylaluminium.

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.