New catalysts based on oxovanadium (IV) and cucurbit[6]uril. / Novos catalisadores à base de oxovanádio (IV) e Cucurbit[6]urila

AUTOR(ES)

Silvânia Marilene de Lima

DATA DE PUBLICAÇÃO

2009

RESUMO

Cucurbiturils are versatile molecules used in several branches of chemistry. These molecular cages form a family of homologues from the condensation of glycoluril and formaldehyde in acidic medium. Their applications range from catalysis, photochemistry, organic and inorganic synthesis, materials and supramolecular chemistry. Particularly cucurbit[6]uril, or simply CB[6], is a very symmetrical molecule, which posesses coordination points on its portals, especially with hard acids. Due to this characteristic, it was possible to synthesize a new complex, with a vanadyl, VO2+, catalytic center bonded to the extremity of the cavitand. The access to the catalytic center of this molecule should be determined by the entrance of the substrate inside the macrocycle, which is limited by its volume and by solvophobicity, because the cavity is strongly hydrophobic. The structure of this new complex could not be completely solved yet, because it was impossible to obtain a single crystal for X-rays diffraction analysis. The solid state characterization techniques indicated that this new complex has its metallic center in a rectangular-base pyramid configuration. This was shown by the spectroscopic evidences which point to a d1 ion in a C2V symmetry. Attempts were made to synthesize both mono and binuclear species, but all the techniques we have used have demonstrated that only the former one was obtained. The first catalytic tests for hydrocarbons convertion in mild conditions have shown good results towards for linear substrates and no activity at all towards more volumous cyclic molecules. The results we have obtained indicate that the alkane oxidation reactions with these complexes occur inside the cavity along the (V=O)2+ ion dz2 orbital , and not on its superior moiety on the vanadyl oxygen atom.

ASSUNTO(S)

complexos catalisadores catalysis oxovanádio(iv) cucurbit[6]uril cucurbit[6]urila oxovanadium(iv). complexes

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