Nitrile Hydration by Co(III) Complex with Oxygenated S Atoms Inserted into Mesoporous Silica

Abstract

Three octahedral Co(III) complexes with N2S2 coordination donors at the equatorial plane and two molecules of tert-butylisocyanide at axial sites were prepared to investigate the hydration of acetonitrile, propionitrile, benzonitrile, and acrylonitrile. The complexes are different in the oxidation state of the coordinated sulfurs; two thiolates (–S; 1), two sulfenates (–SO; 2), and two sulfinates (–SO2; 3). The hydration of the nitriles to their corresponding amides was observed only in the reaction system including 2, indicating that the sulfenate group is essential for the generation of the hydration activity in the series. In order to avoid the deactivation of catalyst 2 by decomposition, it was inserted into the mesopores in the folded sheet mesoporous material (FSM). Indeed, the thermal stability of 2 increased and the reaction turnover number somewhat improved, but the catalyst eluted out from the pores because the electrostatic interaction between silanol groups and polar groups of 2 weakened in an aqueous solution.