Stille Coupling of Alkynyl Stannane and Aryl Iodide, a Many-Pathways Reaction: The Importance of Isomerization

Abstract

The kinetics of the Stille reaction between C 6 Cl 2 F 3 I and PhCCSnBu 3 have been studied for the whole catalytic system and for transmetalations as separate steps. The use of (trifluorodichlorophenyl)palladium derivatives slows down the reactions and allows for the observation of the intermediates cis-and trans-[Pd(C 6 Cl 2 F 3 )I(PPh 3 ) 2 ]. The first is formed in the oxidative addition step and isomerizes to the second. Both were studied as catalysts for the whole cycle. The kinetic study compares the relevance of the transmetalation step on each isomer. The competing transmetalations produce both cis-and trans-[Pd(C 6 Cl 2 F 3 )(PhCC)(PPh 3 ) 2 ]. The former undergoes very fast C-C coupling, while the second accumulates in solution due to extremely slow isomerization. Thus, the system is a case study of the effect of competing pathways in the Stille reaction and its consequences on the performance of the catalytic process.

Base‐Free Cross‐Couplings of Aryl Diazonium Salts in Methanol: PdII–Alkoxy as Reactivity‐Controlling Intermediate

“…Transmetalation in each case is favoured via a trans-T-shaped complex, which requires prior isomerization. [21] Our data suggest that the transmetalation at the Pd II -OMe complex 6 occurs substantially more readily with a boronic acid than with an organostannane, [22] which parallels the experimental findings with 4.…”

Stille Coupling Involving Bulky Groups Feasible with Gold Cocatalyst

“…Furthermore, experiments were carried out to check the influence of the added LiCl, the ligand L, and other effects (Table 3). The reactions can be carried out with similarly good yields using either [PdCl 2 (AsPh 3 ) 2 ] or the intermediate formed after the first oxidative addition to Pd, [Pd(C 6 H 4 CF 3 )I(AsPh 3 ) 2 ], prepared independently,18 as far as excess LiCl is used (entries 1 and 2; also entries 6 and 7). The suppression of added LiCl is very detrimental to the gold cocatalyzed reaction with AsPh 3 .…”

Experimental study of speciation and mechanistic implications when using chelating ligands in aryl-alkynyl Stille coupling

“…12,13 A thorough mechanistic study of the PPh3 case uncovered a many-pathways reaction and revealed that the reason for the partial frustration of PhCC-Rf coupling (Rf = 3,5-C6Cl2F3) is the formation of trans-[Pd(Rf)(CCPh)(PPh3)2], which is reluctant to isomerize to cis as required for coupling. 14 The good results with some chelating ligands suggest that they will enforce the required cis configuration. However, there have not been any detailed mechanistic studies of this process.…”