A viable synthesis of ferrocene tethered NHC–Pd complex via supported ionic liquid phase catalyst and its Suzuki coupling activity

Immobilization of N-Heterocyclic Carbene Compounds: A Synthetic Perspective

“…Lee and co-workers first reported the metalation of PS-supported compound 191 by using Pd­(OAc) 2 as well as an external base Na 2 CO 3 in a mixture of water and DMF (1/1) for the preparation of a PS-supported NHC–Pd complex (Scheme ). Following this work, a series of PS-supported NHC–Pd compounds were prepared through this method. ,,,− In addition to mixed solvent systems, similar to homogeneous conditions, pure solvents such as DMSO, THF, and DMF were reported more frequently for the syntheses of supported NHC–Pd complexes (refs , , , , , , , , , , − ). It should also be mentioned that although an external base was used in several cases to assist the deprotonation of the NHC precursors, it might not be necessary as many examples also described the successful preparation of supported NHC–Pd complexes by mere use of Pd­(OAc) 2 .…”

“…Since ICP-MS provides the best detection limits (1–10 ppt) compared to the others (ICP-AES, 1–10 ppb; AAS, subppb −1 ppb), it can be regarded as a preferred tool for this analysis, while AAS especially the FAAS (sub parts per million) is not recommended. It should be noted that in some publications energy-dispersive X-ray spectroscopy (EDX or EDS) analysis is also employed to determine the loading of an NHC metal complex. ,,, However, the accuracy of this method is debatable as the NHC moieties are not always well-dispersed over the supported material.…”

Reusable Palladium N-Heterocyclic Tetracarbene for Aqueous Suzuki–Miyaura Cross-Coupling Reaction: Homogeneous Catalysis and Heterogeneous Recovery

“…This observation was further supported by high-resolution transmission electron microscopy measurements (Figure S13). The low reactivity of 4h with an electron-donating −OCH 3 group in the reaction might be due to the reluctance of its C–Cl bond to oxidatively add to the Pd center, and Pd was likely to be reduced by boric acid …”

“…As shown in Table 2, the electronic effect of the substituents appeared to be crucial. For aryl chlorides without substituents or with electron-withdrawing groups at different positions (Table 2, entries 1−11), the target cross-coupling products were obtained in excellent yields (93−99%) within 1 h. Meanwhile, the substituent groups on the aryl boric acids have no obvious effect on the coupling reactions under the reaction conditions (Table 2, entries 7− 11). However, aryl chlorides with electron-donating groups, for example, 4-chloroanisole (4h) and phenylboronic acid (5a) coupling (Table 2, entry 12), gave an exceptionally low yield (56%) even at a prolonged reaction time (3 h).…”

“…The low reactivity of 4h with an electron-donating −OCH 3 group in the reaction might be due to the reluctance of its C−Cl bond to oxidatively add to the Pd center, and Pd was likely to be reduced by boric acid. 11 Aryl bromides were more active for the cross-coupling reaction. As shown in Table 2 (entries 13−23), the yields for the target coupled products were in the range of 90−99% within only 0.5 h. Similar to the case for aryl chlorides, lower yields were obtained for an electron-donating group attached to an aryl bromide (Table 2, entry 18).…”