Nitrile Addition to (η4‐Butadiene)zirconocene: The Formation of Organometallic and Metal‐Free Hexatrienediamine Derivatives

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Abstract
(η4‐Butadiene)zirconocene adds one equivalent of benzonitrile to form the five‐membered azazirconacyclopentene derivative 7, which contains an NH group in the ring and a vinyl substituent at the α‐carbon center. The reaction of 7 with an additional equivalent of benzonitrile furnishes the chiral nine‐membered metallacycle ( magnified image ) (12) which may be isomerized to the thermo‐dynamically favored tautomer ( magnified image ) (13). The Gibbs activation energy of the enantiomerization of the trans‐cycloalkene‐like 13 is ΔG#(323 K) = 15.5 ± 0.3 kcal mol‐1. The analogous conformational equilibration of 12 has a lower activation barrier of ΔG# (236 K) = 12.1 ± 0.3 kcal mol‐1; complex 13 is characterized by X‐ray diffraction. Hydrolysis of 13 yields the conjugated 1,6‐diamino‐1,6‐diphenylhexatriene 16 which is characterized by X‐ray diffraction.

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