Formylation of Amines by CO2 Hydrogenation Using Preformed Co(II)/Nickel(II) Complexes.

Preparation of formamides by CO2 hydrogenation requires an efficient catalyst and temperatures around 100 °C or higher, but most catalysts reported so far incorporate rare and toxic precious metals. Five cobalt(II) or nickel(II) complexes with dmpe or PNN (dmpe = 1,2-bis(dimethylphosphino)ethane; PNN = [(2-(di-tert-butylphosphinomethyl)-6-diethylaminomethyl)pyridine) have been evaluated as precatalysts for the hydrogenation of CO2 to prepare formamides from the corresponding secondary amines. The most active catalyst for these reactions was found to be [NiCl2(dmpe)] in DMSO, producing dimethylformamide (DMF) from CO2, H2, and dimethylamine in up to 6300 TON, the highest activity reported for this reaction with an abundant metal-phosphine complex.