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Amination with PdNHC Complexes: Rate and Computational Studies Involving Substituted Aniline Substrates
Author(s) -
Hoi Ka Hou,
Çalimsiz Selçuk,
Froese Robert D. J.,
Hopkinson Alan C.,
Organ Michael G.
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102428
Subject(s) - chemistry , aniline , deprotonation , aryl , reductive elimination , amination , medicinal chemistry , oxidative addition , reactivity (psychology) , catalysis , carbene , derivative (finance) , combinatorial chemistry , organic chemistry , ion , medicine , alkyl , alternative medicine , pathology , financial economics , economics
Abstract The amination of aryl chlorides with various aniline derivatives using the N‐heterocyclic carbene‐based Pd complexes Pd‐PEPPSI‐IPr and Pd‐PEPPSI‐IPent (PEPPSI=pyridine, enhanced precatalyst, preparation, stabilization, and initiation; IPr=diisopropylphenylimidazolium derivative; IPent= diisopentylphenylimidazolium derivative) has been studied. Rate studies have shown a reliance on the aryl chloride to be electron poor, although oxidative addition is not rate limiting. Anilines couple best when they are electron rich, which would seem to discount deprotonation of the intermediate metal ammonium complex as being rate limiting in favour of reductive elimination. In previous studies with secondary amines using PEPPSI complexes, deprotonation was proposed to be the slow step in the cycle. These experimental findings relating to mechanism were corroborated by computation. Pd‐PEPPSI‐IPr and the more hindered Pd‐PEPPSI‐IPent catalysts were used to couple deactivated aryl chlorides with electron poor anilines; while the IPr catalysis was sluggish, the IPent catalyst performed extremely well, again showing the high reactivity of this broadly useful catalyst.