resumo
The cyclopentadienyl metal-carbonyls CpFe(CO)(2)Cl and CPMO(CO)(3)Cl, and their 1:1 inclusion complexes with beta-cyclodextrin (beta-CD) and permethylated beta-CD (TRIMEB), were prepared, and the TRIMEB adduct with CpFe(CO)2Cl was structurally characterized by single-crystal X-ray diffraction. The complex crystallizes in the orthorhombic space group P2(1)2(1)2(1), with a = 11.189(3) angstrom, b = 25.149(6) angstrom, c = 28.964(7) angstrom and Z = 4 formula units. One CpFe(CO)(2)Cl guest molecule, disordered over two sites, is completely enclosed in the TRIMEB cavity. The cyclodextrin molecules pack in columns parallel to the crystallographic a axis and make an angle of 33.6 degrees with the bc plane. The oxidative decarbonylation of the free and encapsulated complexes by aqueous tert-butylhydroperoxide (t-BuOOH) or aqueous H2O2 was studied at room temperature by quantifying the CO/CO2 liberated in the gas phase. When CPMo(CO)(3)Cl is encapsulated in CDs, the extent of the decarbonylation by t-BuOOH is reduced. The use of H2O2 as oxidant modifies the reactivity in an unexpected fashion. Thus, the beta-CD adduct almost totally resists oxidation by H2O2, whereas the TRIMEB adduct decarbonylates faster than the nonincluded complex during the early stages of the reaction. CPMo(CO)(3)Cl and the two inclusion complexes were examined as catalyst precursors for the epoxidation of cyclooctene at 295 or 328 K, using t-BuOOH in decane or water, or aqueous H2O2, as oxidants. Although the free complex is essentially inactive as a catalyst precursor with aqueous H2O2, the introduction of CDs to the system instills significant catalytic activity, with cyclooctene oxide being the only observed reaction product.
palavras-chave
CYCLOPENTADIENYL-MOLYBDENUM COMPLEXES; PERMETHYLATED BETA-CYCLODEXTRIN; CYCLOOCTENE EPOXIDATION; MESOPOROUS MATERIALS; INCLUSION-COMPOUNDS; TUNGSTEN COMPLEXES; WATER; PRECURSORS; KINETICS; HEPTAKIS(2,3,6-TRI-O-METHYL)-BETA-CYCLODEXTRIN
categoria
Chemistry
autores
Balula, SS; Coelho, AC; Braga, SS; Hazell, A; Valente, AA; Pillinger, M; Seixas, JD; Romao, CC; Goncalves, IS
nossos autores
Anabela Tavares Aguiar Valente
Investigador Principal
Isabel Maria de Sousa Gonçalves
Professor associado