Abstract
Three-coordinate bipyridyl complexes of gold, [(κ2-bipy)Au(η2-C2H4)][NTf2], are readily accessed by direct reaction of 2,2'-bipyridine (bipy), or its derivatives, with the homoleptic gold ethylene complex [Au(C2H4)3][NTf2]. The cheap and readily available bipyridyl ligands facilitate oxidative addition of aryl iodides to the Au(I) center to give [(κ2-bipy)Au(Ar)I][NTf2], which undergo first aryl-zinc transmetalation and second C-C reductive elimination to produce biaryl products. The products of each distinct step have been characterized. Computational techniques are used to probe the mechanism of the oxidative addition step, offering insight into both the origin of the reversibility of this process and the observation that electron-rich aryl iodides add faster than electron-poor substrates. Thus, for the first time, all steps that are characteristic of a conventional intermolecular Pd(0)-catalyzed biaryl synthesis are demonstrated from a common monometallic Au complex and in the absence of directing groups.
Highlights
The development of the chemistry of gold has been one of the most striking research themes of recent times
Of particular interest was the chemistry of cationic [bipyAu(alkene)]+ complexes bearing a variety of substituted 2,2′bipyridyl frameworks
This order of reactivity is in agreement with the trend reported by Amgoune, Bourissou, et al for the process outlined in Scheme 1B14 and Article contrasts to the reactivity of Pd(0) toward aryl iodides, where electron-poor substrates have been shown to react faster.[23]
Summary
The development of the chemistry of gold has been one of the most striking research themes of recent times. The putative steps in a potential redox gold cycle are analogous to those of Pd(0)-catalyzed cross-couplings, consisting of oxidative addition, transmetalation, and reductive elimination (Scheme 1A).[4] Of these, it is recognized that the oxidative addition step is challenging, due to the “redox gold problem” outlined above. Most commonly this is circumvented by employing an external oxidant, which facilitates the Au(I) → Au(III) transformation and allows the catalytic coupling of two formally nucleophilic partners;[5,6] the requirement of a strong external oxidant limits the attractiveness of this strategy. Following the submission of this article, Amgoune, Bourissou, and co-workers published a Au(I)/Au(III) catalytic cycle involving a sequence of C−X oxidative addition, C(sp2)− H auration, and reductive elimination, by employing a P,Nligand (Me-Dalphos) on gold.[17]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call