Zirconium bisamides

Attempts to hydroaminate ethylene, aUylbenzene, and norbornene with ArNH2 in the presence of zirconium bisamides Cp2Zr(NHAr)2 (Ar = 2,6-Me2CsH3, o-MeQH4) at temperatures up to 160°C have been unsuccessful [126]. 

In 1992, Bergman et al. reported that zirconium bisamides Cp2Zr(NHR)2 catalyze the intermolecular hydroamination of alkynes with sterically hindered primary amines to give enamines or their tautomeric imines (e.g., Eq. 4.77) [126]. 

Scheme 4-15 Catalytic cycle for the zirconium(bisamide)-catalyzed hydroamination of alkynes...

Although zirconium bisamides Cp2Zr(NHAr)2 do not catalyze the hydroamination of alkenes (see above), they are catalyst precursors for the hydroamination of the more reactive double bond of allenes to give the anti-Markovnikov addition product (Eq. 4.96) [126]. 

Hydroamination of alkynes.1 Zirconium bisamides can react with internal alkynes at 85-120 to form azametallacyclobutcncs, which can dissociate to Cp Zr=NR and an enamine (equation I). 

Of more practical value zirconium bisamides can serve as catalysts for reaction of primary amines with alkynes to form cnamines. This reaction cannot be extended to alkenes, but allenes undergo this hydroamination to form imincs. 

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