Heterogenization of a Molecular Ni Catalyst within a Porous Macroligand for the Direct C–H Arylation of Heteroarenes

Abstract

Direct C-H functionalization catalyzed by a robust and recyclable heterogeneous catalyst is highly desirable for sustainable fine chemical synthesis. Bipyridine units covalently incorporated into the backbone of a porous organic polymer were used as a porous macroligand for the heterogenization of a molecular nickel catalyst. A controlled nickel loading within the porous macroligand is achieved and the nickel coordination to the bpy sites is assessed at the molecular level using IR and solid-state NMR spectroscopy. The heterogenized Ni-bpy catalyst was successfully applied to the direct and fully selective C2 arylation of benzothiophenes, thiophene and selenophene, as well as for the arylation of free NH-indole. Recyclability of the catalyst was achieved by employing hydride activators to reach a cumulative turnover number of more than 300 after seven cycles of catalysis, which corresponds to a total productivity of 12 grams of 2-phenylbenzothiophene, chosen as model target biaryl, per gram of catalyst.

Metalated Porous Phenanthroline‐Based Polymers as Efficient Heterogeneous Catalysts for Regioselective C−H Activation of Heteroarenes

“…for different time (Figure 2A), liquid 1 H NMR analysis shows the yield up to 38.0% of deuterium incorporation; When the parallel experiments were performed starting from the benzo[b]thiophene‐d 1 , LiHMDS, and H‐HMDS, liquid 1 H NMR analysis shows 52.0% yield of proton incorporation (Figure 2B). These results indicate that LiHMDS is able to activate the C−H bond of benzothiophene, forming lithiated benzothiophene species, but only a small amount of the species existed in the toluene [15] . However, the lithiated species is constantly consumed and reformed during the reaction process, thus promoting the reaction (Scheme S2).…”

“…The LiHMDS is nonpolar dimer in toluene but polar monomeric species in 1.4‐dioxane or THF. As a result, LiHMDS is easier to enter the porous organic polymer in toluene than that in the others [14,15] …”

“…Notably, a direct reuse of POP‐Phen@Ni‐2 has only a trace of product (Table S2, entry 8), which might be resulted from the formation of Ni(Phen)(HMDS)x species [16] . Treatment with sodium borohydride (NaBH 4 ) at 50 °C for 30 min, the used POP‐Phen@Ni‐2 showed similar activity to that of the fresh POP‐Phen@Ni‐2 [15] . After recycling for 5 times, the POP‐Phen@Ni‐2 still showed high activity (Figure 4), indicating that the POP‐Phen@Ni‐2 has a good recyclability.…”

“…This non‐noble metal‐based catalyst shows excellent catalytic performances, but difficulty for separating this catalyst from homogeneous system strongly hinders its wide application. The solution of this issue is to develop highly efficient heterogeneous catalysts [15] …”

Rational design of bifunctional conjugated microporous polymers

“…Given this, Canivet and co-workers described a family of bipyridine-based CMPs with different loading of Ni metal sites, which were explored for the potential in the catalytic performance of benzothiophene C-H arylation; and the results indicate that these Ni-dopped CMPs with abundant active sites possess high catalytic activities and wide scope of applicable substrates. 114 It is obvious that with the aid of post-synthetic modification, we can tune the metal loading in the CMP network precisely and control its chemically active functionalities in accordance with requirements without the damage of the extended -conjugation in structure, thereby the high porosity of CMPs retains Please do not adjust margins Please do not adjust margins which promises the effective molecule transportation in CMPs after the functionalization.…”