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We have investigated theregiochemistry of the stoichiometric and catalytic hydroamination of disubstituted alkynes by imidozirconium complexes. The addition of alkynesto Cp2Zr= NR occurred regioselectively to give metallacycles 2, with the larger alkyne substituent RL located a to the metal center. Hydrolysisof the metallacycles then gave enamines and their tautomeric imines which were the net result of anti-Markovnikov addition to the alkyne. The size of the R group on the imido ligand and the size of the alkyne were influential in determining the degree of regioselectivity. By utilizing Cp2 (THF) Zr= NR to generate Cp2Zr= NR at room temperature and Cp2Zr (R')(NHR) to generate Cp2Zr= NR at high temperature, it was determined that the thermodynamic and kinetic regioselectivities were nearly identical for dialkylacetylenes. In contrast, for 1-phenylpropyne, the thermodynamic regioselectivity was found to be …