Premium
Nitrile Addition to (η 4 ‐Butadiene)zirconocene: The Formation of Organometallic and Metal‐Free Hexatrienediamine Derivatives
Author(s) -
Erker Gerhard,
Pfaff Ronald,
Krüger Carl,
Nolte Matthias,
Goddard Richard
Publication year - 1992
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19921250724
Subject(s) - chemistry , benzonitrile , nitrile , substituent , metallacycle , racemization , ring (chemistry) , gibbs free energy , stereochemistry , tautomer , medicinal chemistry , x ray crystallography , crystallography , organic chemistry , diffraction , physics , optics , quantum mechanics
(η 4 ‐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 () ( 12 ) which may be isomerized to the thermo‐dynamically favored tautomer () ( 13 ). The Gibbs activation energy of the enantiomerization of the trans ‐cycloalkene‐like 13 is Δ G # (323 K) = 15.5 ± 0.3 kcal mol ‐1 . The analogous conformational equilibration of 12 has a lower activation barrier of Δ G # (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.