G. Attilio Ardizzoia

Two mixed ligand copper(I) complexes, [Cu(PPh 3 ) 3 ( κ ‐O‐mand)] ( CuP3M ) and [Cu(PPh 3 ) 2 ( κ 2 ‐O,O’‐mand)] ( CuP2M ) (mand= dl ‐mandelate) were synthesized and fully characterized. The different coordination modes of the α‐hydroxycarboxylate ligand in CuP2M and CuP3M are clearly demonstrated by infrared spectroscopy, with the asymmetric ν C=O stretching being observed at 1626 ( CuP3M ) and 1593 ( CuP2M ) cm −1 , respectively. Solution NMR studies ( 1 H, 31 P{ 1 H}), elemental and X‐ray structure analyses confirmed the nature of the synthesized compounds. Complexes CuP2M and CuP3M were active in carbene transfer reactions towards unsaturated bonds, using ethyl diazoacetate (N 2 CHCOOEt, EDA) as carbene source. Indeed, they promoted the trans ‐diastereoselective cyclopropanation of terminal and internal olefins under mild reaction conditions and low catalyst loading (1 % mol).