Highly Efficient Aluminum-Catalyzed Hydro-amination/-hydrazination of Carbodiimides

The catalytic activity of commercially available [Al(NMe2)(3)](2) (1) and a dimethyl aluminum guanidinate complex toward the hydro-aminationi-hydrazination of carbodiimides was studied. The guanidinate-supported complex 2 was prepared via salt metathesis reactions of AlMe2Cl and an in situ generated lithium guanidinate reagent. X-ray crystallographic studies revealed the influence of the guanidinate ligand on the Al metal center. Hydroamination reactions were successfully carried out at room temperature with 2 as the catalyst, while 1 proved to be ineffective under these conditions. On the contrary, both 1 and 2 were active toward the hydro-hydrazination of carbodiimides, which were run at elevated temperatures (120 degrees C). Consequently, the reaction temperature had a significant influence on the choice of the catalyst since the catalytically active species can be generated from various precatalysts under different conditions. The formation of guanidines and aminoguanidines showed a high functional group tolerance and typically proceeded with excellent yields at low catalyst loadings. X-ray crystallographic studies of compound 4a revealed interesting structural features of the previously unknown aminoguanidine products. The independently isolated Al aminoguanidinate complex 5 showed catalytic activity toward hydro-hydrazination chemistry and provided valuable evidence in support of the proposed reaction mechanism.