ESI-MS Studies in Mizoroki-Heck and Related Reactions

Two specific reactions were studied the arylation of n-butyl vinyl ether (25) with two different trifiates, 1-naphthyl triflate (26), and 4-cyanophenyl trifiate (27). The four catalytic systems studied were based on palladacycles 30 and 31, pincer complex 32, Pd(OAc)2 and polyurea encapsulated Pd EnCat30. The authors used dppp (l,3-bis(diphenylphosphino)propane) (33) and (2S,4S)-(-)-2,4-bis(diphenylpho- 

Entry Aryl triflate Palladium source Additive Species observed by ESI-MS 

The insertion of w-butyl vinyl ether (25), which would be the next step in the mechanism postulated by the Mizoroki-Heck reaction, was not observed in any case. The authors suggest that such complexes were either present in very low concentrations or just too unstable to be detected by ESI-MS. 

The study started by selecting an oxidative Heck coupling between arylboronic acid Sc, enamide 36a, and 2,9-dimethyl-l,10-phenanthroline (38) as the ligand. The aliquots were taken from the reaction mixture after 3 h at room temperature and diluted with acetonitrile in a 1 10 ratio before being injected into the mass spectrometer. Table 7.8, showing the detected organopalladium intermediates found in this study, supports the typically catalytic cycle of an oxidative Heck reaction. Entry 1 shows all the intermediates observed during the whole process. 

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