Enantioselective addition of diethylzinc to aromatic aldehydes catalyzed by chiral BINOL-functionalized nanoporous graphene oxides

The supporting material on which an asymmetric catalytic reaction takes place has proved to be an important component which could influence the efficiency and sometimes enantioselectivity of a heterogeneous asymmetric reaction. On the other hand, graphene oxide (GO) has attracted broad attentions because of its unique characteristics and potential applications in many fields. However, GOs have been rarely employed as the supporting materials for heterogeneous catalytic reactions, especially those enantioselective reactions. Herein, a new type of GO-based heterogeneous catalyst was prepared for enantioselective addition of diethylzinc to aromatic aldehydes. To produce this GO catalyst, commercial GO was firstly oxidized in an acidic environment to make nanoporous GOs and then enantiopure (R) or (S)-NH₂-BINOLs were attached (covalently) onto the nanoporous GOs, and this GO-BINOL was subsequently treated by using Ti(OⁱPr)₄. The as-prepared GO-BINOL-Ti catalyst displayed good reactivity (99%) and modest enantioselectivity (45% ee) in the following asymmetric addition reactions. We expect this preliminary demonstration could inspire the research by using GO as heterogeneous catalytic supports and could improve the enantioselectivity later.