Selectivity control of oxygen transfer reactions catalyzed by the ruthenium complexes with monodentate oxygen or nitrogen ligand bound to FSM

Abstract

Two kinds of immobilized ruthenium complex with tetradentate BABP (6,6′-bis(benzoylamino)-2,2′-bipyridine) ligand are prepared. One is compound 1 (FSM-Ru) directly bound to silica of the FSM-surface through Ru–O–Si bond, and others are compounds 2 (FSM-Aps-Ru) and 3 (FSM-Ims-Ru) with monodentate nitrogen ligands bound to silica surface. These ruthenium complexes encapsulated into mesopore of FSM showed interesting activity for oxygen transfer reaction of cyclohexene using tert-butylhydroperoxide (TBHP) as an oxidant. The FSM-Ru catalyst ( 1) having oxygen donor gave 1,2-epoxycyclohexane (epoxide) selectively through stepwise addition of TBHP, although 2 and 3 having nitrogen donor gave 2-cyclohexen-1-yl tert-butyl peroxide (peroxide) mainly. This remarkable selectivity control in the oxygen transfer reaction is interpreted in terms of the trans-influence of the ruthenium complex with the axially coordinating monodentate ligand on the silica support. Moreover, the heterogeneous catalyst 1 was recycled and used three times in epoxidation of cyclohexene, since leaching of the ruthenium species from 1 was not observed under argon atmosphere.