Enhanced Reactivity Results in Reduced Catalytic Performance: Unexpected Ligand Reactivity of a Bis(N-2,6-diisopropylphenylperflourophenyl-amidate)titanium-bis(diethylamido) Hydroamination Precatalyst
journal contributionposted on 02.04.2020 by Jason A. Bexrud, Chunyu Li, Laurel L. Schafer
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A bis(amidate)titanium-bis(amido) complex incorporating electron withdrawing pentafluorophenyl substituents has been prepared to enhance reactivity in this class of hydroamination precatalyst. This bis(N-2,6-diisopropylphenylperflourophenylamidate)titanium-bis(diethylamido) titanium complex has been fully characterized, including its X-ray crystal structure. As a precatalyst, the title compound proved to be effective for intermolecular hydroamination of internal and terminal alkynes with primary amines with yields as high as 97% and modest intramolecular alkene hydroamination. However, the elevated reactivity of this complex also resulted in reduced Markovnikov/anti-Markovnikov selectivity with some terminal alkynes. Substrate scope limitations revealed that this complex is susceptible to decomposition as a direct consequence of nucleophilic addition of the amine substrate to the pentafluorophenyl substituent of the amidate ligand.