Cu(I) complexes containing a multidentate and conformationally flexible dibenzylidene acetone ligand (dbathiophos): application in catalytic alkene cyclopropanation

The synthesis and characterisation of a multidentate conformationally flexible ligand based on the dibenzylidene acetone core structure, dbathiophos (1), is described. Ligand 1 has a high affinity for cationic and neutral Cu(I) species. Three unique Cu(I) complexes (4-6) are reported showing that the ligand backbone of dbathiophos is hemilabile, and able to adopt different 1,4-dien-3-one conformational geometries around Cu(I). Complexes 4 and 6 both effectively catalyse the cyclopropanation of styrene with ethyl diazoacetate at low catalyst loadings (1 mol% Cu).