Catalytic hydroacetylenation of carbodiimides with homoleptic alkaline earth hexamethyldisilazides

摘要

The homoleptic alkaline earth hexamethyldisilazides, [M{N(SiMe_3)_2}_2(THF)_2] (M = Mg 1a; Ca 1b; Sr 1c), have been shown to act as efficient precatalysts for the hydroacetylenation of organic carbodiimides with alkyl- and arylacetylenes. Catalytic activity was observed to increase with the size of the group 2 metal centre employed and to be strongly influenced by the steric properties of the carbodiimide substrate. The intermediate dimeric calcium and strontium bis(amidinate) complexes, [{PhCuCC(N~iPr)_2}_2M]_2 (M = Ca 2b, Sr 2c), have been isolated and crystallographically characterised. Kinetic studies using the strontium precursor, 1c, provided a reaction rate law independent of [acetylene] but proportional to [carbodiimide]~2 and inversely proportional to the concentration of the amidine product in solution.