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

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.