Coordination chemistry of Co complexes containing tridentate SNS ligands and their application as catalysts for the oxidation of n-octane.

Abstract

The selective oxidation of saturated hydrocarbons to terminal oxygenates under mild catalytic conditions has remained a centuries long challenge in chemical catalysis. In an attempt to address this challenge, two series of tridentate donor ligands {2,6-bis(RSCH2)pyridine and bis(RSCH2CH2)amine [R = alkyl, aryl]} and their respective cobalt complexes {Co[2,6-bis(RSCH2)pyridine]Cl2 and Co[bis(RSCH2CH2)amine]Cl2} were synthesized and characterized. Crystal structures of Co[2,6-bis(RSCH2)pyridine]Cl2 [R = -CH3 (), -CH2CH3 (), -CH2CH2CH2CH3 () and -C6H5 ()] are reported in which crystallized as a homo-bimetallic dimer that incorporated two bridging chloride atoms in an octahedral geometry around each cobalt center, while , and crystallized as mono-metallic species characterized by trigonal bipyramidal arrangement of ligands around each cobalt center. As catalysts for the homogeneous selective oxidation of n-octane, the catalysts yielded ketones as the dominant products with a selectivity of ca. 90% for the most active catalyst Co[bis(CH2CH2SCH2CH2)amine]Cl2 () at a total n-octane conversion of 23%. Using tert-butyl hydroperoxide (TBHP) as an oxidant, optimization of reaction conditions is also reported.