Encapsulated Neutral Ruthenium Catalyst for Substrate‐Selective Oxidation of Alcohols

Abstract

The neutral complex dichloro-{diethyl [(5-phenyl-1,3,4-oxadiazol-2-ylamino)-(4-trifluoro-methylphenyl)methyl]phosphonate} (p-cymene)-ruthenium(II) was encapsulated inside a self-assembled hexameric host obtained upon reaction of 2,8,14,20-tetra-undecyl-resorcin[4]arene and water. The formation of an inclusion complex was inferred from a combination of spectral measurements (MS, UV/Vis spectroscopy, 1 H and DOSY NMR). The 31 P and 19 F NMR spectra are consistent with motions of the ruthenium complex inside the self-assembled capsule. Molecular dynamics simulations carried out on the inclusion complex confirmed these intracavity movements and highlighted possible supramolecular interactions between the ruthenium first coordination sphere ligands and the inner part (aromatic rings) of the capsule. The embedded ruthenium complex was assessed in the catalytic oxidation (using NaIO 4 as oxidant) of mixtures of three arylmethyl alcohols into the corresponding aldehydes. The reaction kinetics were shown to vary as a function of the substrates' size, with the oxidation rate varying in the order benzylalcohol > 4-phenyl-benzylalcohol > 9-anthracenemethanol. Control experiments realized in the absence of hexameric capsule did not allow any discrimination between the substrates.

Substrate Selectivity Imparted by Self‐Assembled Molecular Containers and Catalysts

“…The first example of encapsulation of the neutral ( p ‐cymene)‐ruthenium(II) catalyst inside a self‐assembled hexameric capsule of resorcin[4]arene was recently reported (Scheme 12). [57] The encapsulation of the neutral arene‐ruthenium(II) complex was thoroughly confirmed by different analytical techniques, in particular 31 P and 19 F NMR spectra suggested a mobility behavior of the complex inside the capsule, that was further supported by molecular dynamics calculations, highlighting possible supramolecular interactions between the complex ligands and the inner surface of the capsule. The system was employed for the catalytic oxidation of mixtures of three arylmethyl alcohols to the corresponding aldehydes, using NaIO 4 as oxidant.…”

Noncovalent tailoring of coordination complexes by resorcin[4]arene-based supramolecular hosts

“…6). 47 Therefore, this second coordination sphere strategy by encapsulation enabled it to turn over the original reactivity of the substrates.…”

Supramolecular Handshakes: Characterization of Urea‐Carboxylate Interactions Within Calixarene Frameworks

“…The stability of supramolecular capsules is often attributed to the cooperative effect of intermolecular hydrogen bonds, [36] starting from the almost 30‐years‐known and still very popular hexameric calix[4]resorcinarenes [37] . The confined space (1375 Å 3 ) of this assembly has been used as a catalyst and as the selectivity router for various reactions, with cyclizations being most prominent [2,14,38–41] . The ′glue‐motif′ of many hydrogen‐bonded capsules is the urea moiety, while calix[4]arenes are often used as building blocks for capsule walls due to their bowl‐like shape [42–45] .…”

“…[37] The confined space (1375 Å 3 ) of this assembly has been used as a catalyst and as the selectivity router for various reactions, with cyclizations being most prominent. [2,14,[38][39][40][41] The 'glue-motif' of many hydrogen-bonded capsules is the urea moiety, while calix [4]arenes are often used as building blocks for capsule walls due to their bowl-like shape. [42][43][44][45] Indeed, functionalization of the wide rim of calixarene with urea residues has led to the formation of hydrogen-bonded dimers in apolar solvents, where the control over its formation and the possibility of guest encapsulation (cavity size of � 200 Å 3 ) was extensively investigated by the research groups of Rebek and Böhmer.…”