Imido-Alkyne Coupling in Titanium Complexes:New Insights into the Alkyne Hydroamination Reaction

摘要

Titanium imido complexes [Ti(NR)(N_2~(Ar)N_(py))(L)](N_2~(Ar)N_(py)= MeC(2-C5H4N)(CH2NAr)2,Ar = 4-C6H4-Me or 3,5-C6H3Me2)have been prepared from the corresponding bis(amide)complexes [Ti(N_2~(Ar)N_(py))-(NMe2)2].The reaction chemistry of the imido ligand has been investigated with aryl acetylenes,affording the {2 + 2} cycloaddition products [Ti(N_2~(Ar)N_(py)){kappa~2-N(~tBu)CH=CAr'}](Ar' = Ph and 4-C6H4Me)which represent a catalytic intermediate in the anti-Markovnikov hydroamination of terminal alkynes.Reaction of these azatitanacyclobutene complexes with tert-butylamine completes the catalytic cycle,affording trans-cinnamyl(tert-butyl)amine;conversely,reaction with a second equivalent of alkyne afforded a second insertion product,an azatitanacyclohexadiene [Ti(N_2~(Ar)N_(py)){kappa~2-N(~tBu)CH=C(Ar')C(Ar')= CH}],two examples of which have been characterized by X-ray crystallography.Studies into the catalytic hydroamination of phenyl acetylene with tert-butylamine have been performed and indicate that the formation of an azatitanacyclohexadiene complex represents a deactivation pathway in this catalytic reaction.