Stille Coupling Involving Bulky Groups Feasible with Gold Cocatalyst

Abstract

Gold‐Shuttle: Sperrige Gruppen, die in Stille‐Kupplungen mit Stannanen und kostengünstigen Liganden nicht oder nur langsam reagieren, können mittels Dimetall‐Katalyse effizient gekuppelt werden. Ein Gold‐Cokatalysator befördert die sperrige Gruppe vom Zinn zum Palladium und vermindert dadurch den sterischen Anspruch des Übergangszustands (siehe Schema).

Direct Evidence for Intermolecular Oxidative Addition of σ(SiSi) Bonds to Gold

“…The ability of gold to undergo transmetalation has been illustrated with various main group elements5 and transition metals 5h. 6 The feasibility of syn insertion was recently corroborated for the reaction of alkynes and allenes with silyl gold(I) complexes 7.…”

Comparing Protonolysis and Transmetalation Reactions: Microcalorimetric Studies of C–AuI Bonds in [AuRL] Complexes

“…However, bulky R groups produce comparatively weaker C-Sn bonds due to steric hindrance in RSnBu 3 , and their transmetalation benefits from this bond weakening provided that the reaction rates are facilitated by accessible transition states mediated by gold. 36 Experimental section. All reactions were carried out under nitrogen atmosphere using Schlenk techniques.…”

“…The latter are particularly useful in mechanistic studies because of their informative 19 F NMR spectra. [32][33][34][35][36][37] We also study the strength of the Ph-Au bond in [AuPhL] complexes for L = PPh 3 , PMe 3 , PCy 3 , P(OPh) 3 and IPr). The goal of our work is to obtain experimental thermodynamic values directly related to Au-C bond dissociation energies (BDE) in order to provide solid experimental references to computational or kinetic studies.…”

“…Study of Sn/Au transmetalation reactions. The protonolysis reaction AuRL + HX can be used to compare other transmetalation reactions AuRL + E-X (E = a suitable electrophile) that produce Ar-X and E-R. Our interest in the Sn/Au transmetalation comes primarily from the gold-cocatalyzed reaction that we developed to accelerate slow or non-operative couplings involving bulky aryls, 36,58,59 The dramatic positive effect of gold in this bimetallic catalysis is that the double transmetalation Sn/Au and Au/Pd skips the sterically hindered Sn/Pd direct transmetalation in the case of bulky aryls. We found that the thermodynamics of the Sn/Au transmetalation is very dependent on the R group and on the halogen being transferred.…”

“…Consequently, the transmetalation of bulky groups from Sn to Au(I) is enthalpically favored compared to the transmetalation of electronically similar smaller groups. The Me same reason favors transmetalation to linear Au(I), where this hindrance is released, better than to more crowded Pd(II) complexes, 36,65 which is the basis of the gold co-catalyzed Stille reaction.…”