X-ray Snapshot Observation of Palladium-Mediated Aromatic Bromination in a Porous Complex
† Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
‡ Department of Chemistry, NanoScience Center,University of Jyväskylä, P.O. Box 35, 40014 Jyväskylä,Finland
J. Am. Chem. Soc., Article ASAP
DOI: 10.1021/ja502996h
Publication Date (Web): May 1, 2014
Copyright © 2014 American Chemical Society
Abstract
Pd-mediated aromatic bromination is intriguing to synthetic and organometallic chemists due to both its synthetic utility and, more importantly, a proposed mechanism involving an uncommon Pd(IV)/Pd(II) catalytic cycle. Here, we report an X-ray snapshot observation of a Pd reaction center during a Pd-mediated aromatic bromination in a single crystal of a porous coordination network crystalline scaffold. Upon treatment of a single crystal with N-bromosuccinimide, sequential X-ray snapshots revealed that the aryl-Pd(II)-L species embedded in the network pores was converted to the brominated aryl product through a transient aryl-Pd(II)-Br species, which is normally unobservable because of its rapid dimerization into insoluble Pd2(μ-Br)2 species. Though the reaction pathway may be biased by the crystalline state, the new X-ray snapshot method relies on crystalline flasks to provide important mechanistic insight.
コメント