Abstract
Trimethoxysilane pentacoordinate Schiff-base Co(II) complexes, i.e. Co[Cl-Sal(PMeO-Si)DPTA], (3.a) and Co[F-Sal(PMeO-Si)DPTA], (3.b) and Co[FCl-Sal(PMeO-Si)DPTA], (3.c) (DPTA=bis(aminopropyl)amine, Sal=salicylaldehyde) were synthesized and anchored into SBA-15 matrix to obtain novel supported hybrid catalysts. The catalysts were characterized by FT-IR, TEM, SEM, XRD, TG and BET analysis. These supported complex catalysts were tested in the catalytic oxidation of n-hexane and n-heptane with O2 under relatively mild and solvent free conditions. A high TON of 3320 with 19.6% yield for n-hexane oxidation and a high TON of 3180 with 17.3% yield for n-heptane oxidation were obtained with 3.b anchored over SBA-15. The oxidation product regioselectivities were obtained as C1(1):C2(9.2):C3(10.7) for n-hexane and C1(1):C2(9.0):C3(9.7):C4(2.7) for n-heptane. The reaction of kinetics follows a pseudo first-order reaction for both n-alkanes. Enhanced yields (30.6% for n-hexane oxidation and 23.8% for n-heptane oxidation) were obtained with the addition of PCA (pyrazinecarboxylic acid); the catalytic results of reactions made in the presence of radical traps suggested that the catalytic oxidation of n-hexane and n-heptane proceeded via free radicals. The catalyst recycles tests showed that it could be reused up to 7th catalytic cycles.
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