Silica “SHB”chiral Pc-L* Cu(I) complexes for continuous flow cyclopropanation reactions with carbon dioxide as a carrier

We have recently reported that copper(I) complexes of the new C1-symmetric pyridine-based 12-membered tetraaza macrocycles, Pyridine Containing Ligands (Pc-L*), are competent catalysts in the asymmetric cyclopropanation. In order to improve our catalytic system Cu(I) complexes based on Pc-L* ligands were heterogeneised on mesoporous ordered and non-ordered silicas (Davisil B, MCM-41, etc.) by the Supported by HydrogenBond (SHB) method. Supported catalysts C were tested in enantioselective cyclopropanation in batch conditions showing good catalytic activities employing ethyl diazoacetate (EDA) as carbene precursor in n-hexane. The silica support has a strong influence on the diastereoselective outcome of the reaction, favoring the formation of the more challenging cis-isomer. Then, C were tested as catalyst for the cyclopropanation reaction under flow conditions focusing our attention on the use of supercritical CO2. Under optimised conditions, the catalyst was stable over at least 10 h of continuous flow, without drop in activity or selectivity.