Single site anchored novel pentacoordinate Schiff-base Co(II) complexes over SBA-15 for selective oxidation (O2) of n-alkanes and kinetic study

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 O 2 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 C 1 (1):C 2 (9.2):C 3 (10.7) for n -hexane and C 1 (1):C 2 (9.0):C 3 (9.7):C 4 (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.