Copper‐Catalyzed Coupling of (E)‐Bromostilbene with Phenols/Azole: ESI‐MS Detection of Intermediates by Using an Ionically‐Tagged Ligand

Abstract

A system based on copper/1,10‐phenanthroline efficiently promotes the coupling between phenols or pyrazole with (E)‐bromostilbene. (E)‐1‐Aryloxy‐1,2‐diphenylethenes were obtained from the coupling with phenols in good to excellent yields (69–90%). The exception was the reaction involving a phenol containing an electron‐withdrawing cyano group that required a longer reaction time and gave only 49% yield. Kinetic studies indicated the participation of the vinyl halide in the rate‐determining step. Under the conditions employed, the activation of the vinyl halide via a radical pathway was discarded using a radical scavenger test. By using an ionically‐tagged 1,10‐phenanthroline derivative as the ligand, various copper‐based ions were detected through ESI(+)‐MS. These ions suggested that formation of the active species [phenCuOAr(HOAr)2] precedes the vinyl halide activation.

Charge-tagged ligands: useful tools for immobilising complexes and detecting reaction species during catalysis

“…92 These cationic ligands were used as probes to detect the intermediates in the copper-catalysed coupling of ( E )-bromostilbene with phenols (Scheme 24). …”

Phosphine-free Heck reaction: mechanistic insights and catalysis “on water” using a charge-tagged palladium complex

“…26 Recently, a positively-charged phenanthroline derivative allowed the ESI-MS interception and characterization of catalytic species involved in the mechanism of Cu-catalysed C-N and C-O couplings. 27 We have already applied the charge-tag strategy to investigate the in situ formation of Pd, Cu and Ni organometallics and the formation of negative Pd centres during the catalytic cycle of the Heck reaction. 28 Our interest in probing the effectiveness of ESI-MS in fully investigating the various aspects of reaction mechanisms and interactions [29][30][31][32][33][34] has motivated us to use now a palladium complex bearing a charge-tagged ligand (imidazolium derivative) to investigate the neutral Heck reaction.…”

Cellulose Oxidation and the Use of Carboxyl Cellulose Metal Complexes in Heterogeneous Catalytic Systems to Promote Suzuki-Miyaura Coupling and C−O Bond Formation Reaction

“…32 The reaction that followed was similar to those described in the literature. 33,34 Also a comparison with standard catalyst cupper acetate catalyst was performed to observe the catalytic activity of the CuCC. The reaction was performed according to Scheme 2.…”