Hydroaminations substrates, cycloaddition

The reaction involves initial formation of the zirconium-imido species, followed by [2-1-2] cycloaddition with the C—C unsaturation (Scheme 13). This is consistent with the observation that bis(amidate) complexes do not mediate hydroamination with secondary amine containing substrates. The cyclic transition state of the intramolecular reaction determines the regioselectivity of the reaction followed by successive protonation of the intermediate metallacycle and release of product to regenerate the catalyticaUy active imido species. 

Previously reported bis(amidate)- and tethered-amidate-supported zirconium complexes can be used for alkene hydroamination catalysis, and all substrate scope and mechanistic investigations of these systems are consistent with the [2+2] cycloaddition mechanistic profile [61, 62). However, more recent catalyst systems that can be used with secondary amines show broader substrate scope, similar to that attained by rare earth elements and suggest a mechanistic similarity to that observed for previously intensely investigated rare earth hydroamination catalyst systems [7j. Such complexes are proposed to achieve ring closure via o-bond insertion, and thus, consideration of such a mechanistic profile in this case demanded further investigation. 

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