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• 作者：Anant R. Kapdi ; Adrian C. Whitwood ; David C. Williamson ; Jason M. Lynam ; Michael J. Burns ; Thomas J. Williams ; Alan J. Reay ; Jordan Holmes ; Ian J. S. Fairlamb
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：June 5, 2013
• 年：2013
• 卷：135
• 期：22
• 页码：8388-8399
• 全文大小：749K
• 年卷期：v.135,no.22(June 5, 2013)
• ISSN：1520-5126

文摘

Pd⁰b>2b>(dba)b>3b> (dba = E,E-dibenzylidene acetone) is the most widely used Pd⁰ source in Pd-mediated transformations. Pd⁰b>2b>(dba-Z)b>3b> (Z = dba aryl substituents) complexes exhibit remarkable and differential catalytic performance in an eclectic array of cross-coupling reactions. The precise structure of these types of complexes has been confounding, since early studies in 1970s to the present day. In this study the solution and solid-state structures of Pd⁰b>2b>(dba)b>3b> and Pd⁰b>2b>(dba-Z)b>3b> have been determined. Isotopic labeling (²H and ¹³C) has allowed the solution structures of the freely exchanging major and minor isomers of Pd⁰b>2b>(dba)b>3b> to be determined at high field (700 MHz). DFT calculations support the experimentally determined major and minor isomeric structures, which show that the major isomer of Pd⁰b>2b>(dba)b>3b> possesses bridging dba ligands found exclusively in a s-cis,s-trans conformation. For the minor isomer one of the dba ligands is found exclusively in a s-trans,s-trans conformation. Single crystal X-ray diffraction analysis of Pd⁰b>2b>(dba)b>3b>路CHClb>3b> (high-quality data) shows that all three dba ligands are found over two positions. NMR spectroscopic analysis of Pd⁰b>2b>(dba-Z)b>3b> reveals that the aryl substituent has a profound effect on the rate of Pd-olefin exchange and the global stability of the complexes in solution. Complexes containing the aryl substituents, 4-CFb>3b>, 4-F, 4-t-Bu, 4-hexoxy, 4-OMe, exhibit well-resolved ¹H NMR spectra at 298 K, whereas those containing 3,5-OMe and 3,4,5-OMe exhibit broad spectra. The solid-state structures of three Pd⁰b>2b>(dba-Z)b>3b> complexes (4-F, 4-OMe, 3,5-OMe) have been determined by single crystal X-ray diffraction methods, which have been compared with Goodson鈥檚 X-ray structure of Pd⁰b>2b>(dba-4-OH)b>3b>.