Alkaline earth metal oxides as solid bases for ligand-free Heck reaction

Alkaline earth metal oxides (MO, M = Mg, Ca, Sr and Ba) are investigated as solid bases for ligand-free Heck reaction (Pd concentration: 0.05 mol%). SrO is efficient to promote Heck arylation of styrene with bromobenzene (BB). However, aryl amination of BB to form N,N-dimethylaniline is also observed with SrO. CaO-n particles (n: calcination temperature) are prepared by calcination of dried Ca(NO3)2 aqueous solution at 700 or 900 °C. The CaO-n particles outperform other alkaline earth metal oxides considering both BB conversion and selectivity to Heck products. The CaO-900 particles show better performance than the CaO-700 particles. This is attributed to their platelet morphology with sharp edges and corners and the preferential growth along the (1 1 1) crystal plane.