title: Heck alkynylation (copper-free Sonogashira coupling) of aryl and heteroaryl chlorides, using Pd complexes of t-Bu2(p-NMe2C6H4)P: understanding the structure-activity relationships and copper effects.
abstract: L(2)Pd(0) and L(2)Pd(II) complexes, where L= t-Bu(2)(p-NMe(2)C(6)H(4))P, have been identified as efficient catalyst systems for the Heck alkynylation of a variety of aryl bromides (17 examples) and aryl/heteroaryl chlorides (31 examples) with a range of aryl- and alkyl-acetylenes in excellent yields, under relatively low Pd loadings. The single-crystal X-ray structure determination of the presumably active catalytic species, L(2)Pd(0), was carried out in this study to better understand the superior activity of the current catalyst system from a structure-activity relationship point of view. The P-Pd-P bond angle indicates that the complex is bent (174.7°) in comparison to the perfectly linear (180.0°) structure of the analogous Pd(t-Bu(3)P)(2). Preliminary mechanistic studies on the negative copper effect and substrate effect of aryl acetylenes were conducted to better understand the cross-coupling pathway of Heck alkynylation.
authors.affiliation: Johnson Matthey Catalysis and Chiral Technologies, 2001 Nolte Drive, West Deptford, New Jersey 08066, USA.
authors.forename: Xiaotao
authors.initials: X
authors.lastname: Pu
authors.forename: Hongbo
authors.initials: H
authors.lastname: Li
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Colacot