The mechanism of the Stille reaction investigated by electrospray ionization mass spectrometry.
On-line monitoring of Stille reactions was performed via direct infusion electrospray ionization mass spectrometry (ESI-MS) and its tandem version (ESI-MS/MS). When operated in the positive ion mode, ESI(+)-MS was able to transfer, directly from solution to the gas phase, the species involved in all main steps of a Stille reaction, that is, the catalytically active palladium species Pd(PPh3)2, in its molecular ion form as well as the key cationic Pd(II) intermediates, including cyclic IPd-(CH2CH)Sn species. When searching for anionic species, ESI(-)-MS monitoring showed I- as the only anion detectable in the reaction medium. A detailed catalytic cycle for a Stille reaction was elaborated in which reaction intermediates and the previously elusive catalytically active Pd(0) species are shown in association with the respective ionic species intercepted by ESI-MS and further characterized by ESI-MS/MS.
Santos
Leonardo S
LS
Laboratory of Asymmetric Synthesis, Chemistry Institute of Natural Resources, Universidad de Talca, P.O. Box 747, Talca, Chile. lssantos@utalca.cl
Rosso
Giovanni B
GB
Pilli
Ronaldo A
RA
Eberlin
Marcos N
MN