Zirconium complexes imides

While metallocenes are ubiquitous in organometallic and polymer chemistry, few such complexes have been reported to catalyze the Diels-Alder process in high enantioselectivity [127,128,129]. Thebis(tetrahydroindenyl)zirconium tri-flate 60 and the corresponding titanocene are electrophilic to the extent that they catalyze the low-temperature cycloadditions of acrylate and crotonate imides with cyclopentadiene with good diastereoselectivity and excellent enantioselec-tion (Scheme 48). The reactivity of 60 is noteworthy since the corresponding reaction using the crotonyl imide with highly reactive catalysts 31a or 44 requires temperatures of -15 and 25 °C, respectively. 

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