Phosphine/N-heterocyclic carbene palladium complex for Suzuki-Miyaura cross-coupling reactions: The role of water on activity

Abstract

A new bidendate ferrocenyl phosphine/N-heterocyclic carbene (NHC) palladium complex rac-6, bearing a functionalized pendant arm for further grafting on a solid surface, has been synthesized in good yields and fully characterized. The molecular structure of proligand rac-4-BF4 and complex rac-6 were obtained by X-ray diffraction on single crystals. Kinetic studies demonstrated the good activity and stability of rac-6 in the Suzuki-Miyaura coupling of aryl bromides with arylboronic acids. The catalyst proved also to be active for the coupling of more challenging, bulky substrates such as 1-bromo-2-methylnaphthalene and naphthylboronic acid at relatively mild temperatures (40-70°C) and low loadings (0.1-0.5 mol%). Experiments carried out with various amounts of water highlighted the role of water on both activity and mechanism.

Amphiphilic polymeric nanoreactors containing Rh(i)–NHC complexes for the aqueous biphasic hydrogenation of alkenes

“…We imagine that the presence of water, on the contrary, may facilitate the formation of metal nanoparticles, which is a commonly observed phenomenon also for palladium catalysts bearing NHC ligands. 90 Conversely, no black precipitate was observed at the end of the reaction with the nanocatalysts, which is consistent with the catalyst confinement within the CCM hydrophobic environment, from which water as a bulk phase is excluded. Thus, water cannot exert its action to promote the metal reduction and the observed behaviour may correspond to that observed for the molecular complex under homogeneous conditions, except for the much greater catalytic activity.…”

Forever young: the first seventy years of ferrocene

“…Representative examples of such compounds shown in Scheme 17 include chiral carbenes derived from Ugi's amine ( 57 and 58 ) 138 and carbenes possessing additional donor groups, e.g. , oxazolinyl ( 59 ) 139 and phosphine ( 60 , 140 61 R : R = H, 140 a ,141 Me, 142 and 62 143 ), which were employed in asymmetric catalysis.…”

Recent Advances in Catalysis Involving Bidentate N-Heterocyclic Carbene Ligands

“…Most recent reports regarding functionalized NHC ligands, related palladium complexes and their application in C-C coupling reaction have been published by Engle et al and Deydier et al [ 201 , 202 ].…”