18908-74-2Relevant articles and documents
Catalyst activation, deactivation, and degradation in palladium-mediated negishi cross-coupling reactions
B?ck, Katharina,Feil, Julia E.,Karaghiosoff, Konstantin,Koszinowski, Konrad
, p. 5548 - 5560 (2015)
Pd-mediated Negishi cross-coupling reactions were studied by a combination of kinetic measurements, electrospray-ionization (ESI) mass spectrometry, 31P NMR and UV/Vis spectroscopy. The kinetic measurements point to a rate-determining oxidative addition. Surprisingly, this step seems to involve not only the Pd catalyst and the aryl halide substrate, but also the organozinc reagent. In this context, the ESI-mass spectrometric observation of heterobimetallic Pd-Zn complexes [L2PdZnR]+ (L=S-PHOS, R=Bu, Ph, Bn) is particularly revealing. The inferred presence of these and related neutral complexes with a direct Pd-Zn interaction in solution explains how the organozinc reagent can modulate the reactivity of the Pd catalyst. Previous theoretical calculations by Gonzlez-Prez et al. (Organometallics 2012, 31, 2053) suggest that the complexation by the organozinc reagent lowers the activity of the Pd catalyst. Presumably, a similar effect also causes the rate decrease observed upon addition of ZnBr2. In contrast, added LiBr apparently counteracts the formation of Pd-Zn complexes and restores the high activity of the Pd catalyst. At longer reaction times, deactivation processes due to degradation of the S-PHOS ligand and aggregation of the Pd catalyst come into play, thus further contributing to the appreciable complexity of the title reaction. Catalytic complexity: The Pd catalyst used in Negishi cross-coupling reactions shows an unexpected heterogeneity and complexity. Among the various species observed in solution, heterobimetallic Pd-Zn complexes are of particular interest (see figure). These species also seem key to understanding the kinetics of Negishi cross-coupling reactions. S-PHOS=2-dicyclohexylphosphino-2,6-dimethoxybiphenyl.
Super electron donor-mediated reductive desulfurization reactions
Nozawa-Kumada, Kanako,Ito, Shungo,Noguchi, Koto,Shigeno, Masanori,Kondo, Yoshinori
, p. 12968 - 12971 (2019/11/05)
The desulfurization of thioacetals and thioethers by a pyridine-derived electron donor is described. This methodology provides efficient access to the reduced products in high yields and does not require the use of transition-metals, elemental alkali-metals, or hydrogen atom donors.
Expanding the limit of Pd-catalyzed decarboxylative benzylations
Kong, Duanyang,Moon, Patrick J.,Qian, Wenyu,Lundgren, Rylan J.
supporting information, p. 6835 - 6838 (2018/06/26)
The Pd-catalyzed decarboxylative cross-coupling of electron-deficient aryl acetates with aryl bromides is reported. The method widens the scope of benzylic partners that can undergo efficient reactivity from highly activated nitrophenylacetates established previously, to a diverse series of substrates bearing modestly stabilizing groups, allowing direct access to functionalized diarylmethanes. Mechanistic studies support the role of dienolates as key intermediates in the coupling process.
