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.
AlSBA-15 catalysts possessing Brønsted acid and Lewis acid–base bifunctionalities catalyze the direct arylation of benzyl alcohols to diarylmethanes with an 85% product yield through C–O bond activation.
2–8 wt % iron has been grafted over SBA‐15 and 10 wt % alumina grafted SBA‐15 (AlSBA‐15) through selective extraction deposition technique using LaFeO3 as iron precursor in acidic solution. DRS‐UV spectra confirmed the presence of iron as isolated Fe(III), Fe(III)‐clusters and amorphous FeOx oligomers. SEM‐EDX mapping, FT‐IR, XPS, HR‐TEM and 27Al MAS NMR characterisation results confirmed that iron grafted over AlSBA‐15 preferentially reside on the alumina. The donor‐acceptor interaction of grafted iron ions with alumina atoms displaying Lewis acid properties stabilized iron at higher oxidation state Fe(III+δ). This increased the BE of Fe2p electrons (XPS) and shifted the temperature of iron reduction in 2–8 wt %Fe/AlSBA‐15 materials to higher value (600 °C) compared with Fe/SBA‐15 (H2‐TPR). In arylation of benzene, 8 wt %Fe/AlSBA‐15 demonstrated excellent redox catalytic activity with TOF close to homogeneous catalyst and 82 % biphenyl yield. The catalyst demonstrated consistent catalytic performance for 7 cycles.
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