Tetranuclear Zn/4f coordination clusters as highly efficient catalysts for Friedel–Crafts alkylation

Abstract

A series of custom-designed, high yield, isoskeletal tetranuclear Zn/4f coordination clusters showing high efficiency as catalysts with low catalytic loadings in Friedel-Crafts alkylation are described for the first time. The possibility of altering the 4f centers in these catalysts without altering the core topology allows us to further confirm their stability via EPR and NMR, as well to gain insights into the plausible reaction mechanism, showcasing the usefulness of these bimetallic systems as catalysts.

Tuning slow magnetic relaxation behaviour in a {Dy2}-based one-dimensional chain via crystal field perturbation

“…Dy(III) ion is coordinated by nine O atoms from two H 3 L ligands and four carboxylate groups, giving a distorted muffin coordination geometry with C s symmetry by SHAPE analysis (Table S4 † (12) . 23,24 Crystal structure of compound 2. Single crystal X-ray diffraction analysis implies that the structure of 2 is similar to 1 except for one chelated carboxylate group of central Dy(III) ion in 1 replaced by one NCS À ion in 2, leading to the different Fig.…”

Highly Efficient Tetranuclear ZnII2LnIII2 Catalysts for the Friedel–Crafts Alkylation of Indoles and Nitrostyrenes

“…The 1Dy catalyst for both substrates demonstrates a greater rate of quenching than either Zn(OTf) 2 or Dy(OTf) 2 , perhaps indicating a stronger interaction with the metal centres in tandem. Based on the above results and the crystal structure of 1Dy [59] in which a nitrate group chelates to Dy (trans-β-nitrostyrene can be considered as an alternative to nitrate), a plausible mechanism and transition state can be proposed shown in Scheme 2. We envision that the nitroalkenes are activated by chelation to Dy III [44] and π-π stacking between the phenyl group of the coordinating ligand L and the phenyl group of nitroalkenes.…”

“…We recently initiated a project on the synthesis of 3d/4f CCs stabilized by the Schiff base organic ligand H2L [(E)-(2-hydroxy-3-methoxybenzylidene-amino)phenol], that would display catalytic properties [57][58][59]. We also reported the synthesis and characterisation of a series of isoskeletal [60] (Figure 1).…”

“…This precise topology shows that the Zn and the Ln centres are very close (approximately 3.3 Å), permitting both metals to coordinate to the substrates and promote the coupling reaction. Compounds 1Y and 1Dy showed high efficiency as catalysts, at room temperature, with low catalytic loadings in FC alkylation of indole with aldehydes leading to bis-indolylmethane derivatives [59]. A study of the suitability of 1Ln as catalysts in FC alkylation of indole with nitrostyrene is presented herein.…”

“…In 3d/4f chemistry, only a few polynuclear CCs have been successfully used as homogenous catalysts [54][55][56]. We recently initiated a project on the synthesis of 3d/4f CCs stabilized by the Schiff base organic ligand H2L [(E)-(2-hydroxy-3-methoxybenzylidene-amino)phenol], that would display catalytic properties [57][58][59]. We also reported the synthesis and characterisation of a series of isoskeletal [60] tetranuclear Zn II 2Ln III 2 CCs formulated as [Zn II 2Ln III 2L4(NO3)2(DMF)2] (1Ln) where Ln is Y (1Y), Sm (1Sm), Eu (1Eu) Gd (1Gd), Dy (1Dy), Tb (1Tb) and Yb (1Yb) possessing a defect dicubane topology (Figure 1).…”