NDLI: Pd(II)-promoted direct cross-coupling reaction of arenes via highly regioselective aromatic C

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Ishikawa, Atsushi Nakao, Yoshihide Sato, Hirofumi Sakaki, Shigeyoshi
Description	Author Affiliation: Ishikawa A ( Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.)
Abstract	The direct cross-coupling reaction of arenes promoted by Pd(OAc) $_{2}$ is synthetically very useful because the preparation of a haloarene as a substrate is not necessary. This reaction interestingly only occurs in the presence of benzoquinone ( BQ ). DFT, MP2 to MP4(SDQ), and CCSD(T) computations elucidated the whole mechanism of this cross-coupling reaction and the key roles of BQ . The first step is the heterolytic C–H activation of benzo[ h]quinoline ( HBzq ) by Pd(OAc) $_{2}$ to afford Pd(Bzq)(OAc) . The Pd center is more electron-rich in Pd(Bzq)(OAc) than in Pd(OAc) $_{2}$ . Hence, BQ easily coordinates to Pd(Bzq)(OAc) with a low activation barrier to afford a distorted square planar complex Pd(Bzq)(OAc)(BQ) which is as stable as Pd(Bzq)(OAc) . Then, the second C–H activation of benzene occurs with a moderate activation barrier and small endothermicity. The final step is the reductive elimination which occurs with little barrier. The rate-determining step of the overall reaction is the second C–H activation whose activation barrier is considerably higher than that of the first C–H activation . BQ plays a key role in accelerating this reaction; (i) the phenyl group must change its position a lot to reach the transition state in the reductive elimination from the square planar intermediate Pd(Ph)(Bzq)(OAc) but only moderately in the reaction from the trigonal bipyramidal intermediate Pd(Ph)(Bzq)(OAc)(BQ) . This is because BQ suppresses the phenyl group to take a position at a distance from the Bzq . (ii) BQ stabilizes the transition state and the product complex by the back-donation interaction. In the absence of BQ , the reductive elimination step has a much higher activation barrier. Though it was expected that the BQ coordination accelerates the second C–H activation of benzene by decreasing the electron density of Pd in Pd(Bzq)(OAc) , the activation barrier of this second C–H activation is little influenced by BQ .
ISSN	14779226
Issue Number	13
Journal	Dalton Trans.
Volume Number	39
e-ISSN	13645447
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2010-04-07
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Chemistry
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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