A Sustainable Heterogeneous Iron Catalyst Fe/SBA‐15 towards Direct Arylation of Unactivated C(sp³)−H and C(sp²)−H Bonds with Arenes

Abstract

Iron grafted over mesoporous silica (8 wt %Fe/SBA‐15) is a sustainable, efficient heterogeneous iron catalyst for direct arylation of biphenyl methane C(sp3)−H and benzene C(sp2)−H bonds. The selective extraction deposition (SED) technique was adopted to graft iron easily over the mesoporous support SBA‐15 by using LaFeO3 as an iron precursor. The synthesized catalyst has been characterized by EPR spectroscopy, diffuse reflectance UV/Vis spectroscopy, and temperature programmed reduction (TPR) analysis to understand the coordination environment and state of oxidic iron species grafted over the mesoporous SBA‐15. TPR results confirm the presence of isolated, clustered, oligomeric oxidic iron species in the catalyst. The adopted SED technique is highly successful for grafting 8 wt % iron into the mesopores of SBA‐15 without forming iron oxide particles. Unlike homogeneous iron, the 8 wt %Fe/SBA‐15 catalyst does not need support from an electron‐withdrawing group and additives to carry out arylation of benzene and could be successfully recycled five times.

Alumina as Solid‐State Ligand in Enhancing the Redox Catalytic Property of Iron Oxide Grafted AlSBA‐15 towards Arylation of Arene

“…The coupling reaction proceeded neither over AlSBA‐15 catalyst nor with the addition of TEMPO (3 equiv) to the reaction mixture (Table , entry 7, 8) suggesting the involvement of radical species generated by the grafted iron in the coupling process. Therefore, it is expected that reaction may proceed through iron‐assisted single electron transfer (SET), alike our earlier report with 8 wt %Fe/SBA‐15 . The tentative detailed mechanism for the above reaction is given in the supplementary information (Scheme S1).…”

“…Regardless of the content of grafted iron in studied materials, similar TPR profile with multiple reduction events was observed for the SBA‐15 support (Figure a). Occurrence of reduction events at about 410–450 °C, 564 °C, 615–680 °C and above 800 °C are attributed to two‐dimensional oligomeric FeOx species, Fe(III)‐clusters, single site Fe(III) and single site Fe(III) in the micropores of SBA‐15, respectively . The challenge in achieving isolated iron site is clearly evident from the multiple reduction patterns of material grafted with lowest amount of iron 2 wt %Fe/SBA‐15.…”

“…The homogeneous iron (Fe(III) trifluoromethanesulfonate) catalysed arylation of benzene by aryl boronic acid requires suitable expensive additives (substituted 1,10 phenanthroline) to achieve better yield of aryl‐benzenes. In our recent work, we experimented the same reaction over 8 wt %Fe/SBA‐15 with the intention to prove the establishment of Fe(IV) ions in the course of the reaction . However, we obtained low yield of aryl‐benzenes in absence of additives at testing conditions corresponding to that used for testing of the homogeneous iron catalyst with additives.…”

“…Recently, we devised an easy way to graft more isolated iron over the silica support using LaFeO 3 as precursor by selective extraction and deposition (SED) of iron ions in acidic condition ,. With the aim of designing an effective heterogeneous iron catalyst for C−C coupling reaction, in our recent report, by implementing the SED technique 8 wt % of iron was successfully grafted as isolated, cluster and oligomeric oxidic iron species over the high surface area mesoporous silica support (SBA‐15) without forming the bulk iron oxide . The 8 wt %Fe/SBA‐15 was employed as redox catalyst for activation of C( sp 3 )‐H and C( sp 2 )‐H reactions like arylation of biphenyl methane and benzene, respectively.…”

Enhanced Stability of Abundant Amorphous Iron (III) oxide Grafted AlSBA‐15 as Highly Efficient Heterogeneous Fenton Catalyst for the Destruction of Phenol

“…Using the SED technique, recently, we have successfully grafted 8 wt% of iron over mesoporous silica support SBA‐15 (8wt %Fe/SBA‐15) comprising isolated, cluster, and oligomeric oxidic iron species. 8wt %Fe/SBA‐15 demonstrated excellent redox catalytic activity towards arylation of biphenyl methane and benzene involving the C(sp3)‐H and C(sp2)‐H activation, respectively . To our delight, in the arylation of benzene, 8 wt% Fe grafted over alumina coated SBA‐15 (8wt %Fe/AlSBA‐15) exhibited three times more redox catalytic activity than 8wt %Fe/SBA‐15 with turn over frequency close to the homogeneous iron catalyst .…”