Synthesis and characterisation of chiral Cu(I) complexes of substituted pyrrolidine ligands. Efficient catalysts for cyclopropanation reactions

A series of new copper(I) complexes of chiral bidentate N,N'-ligands ((S)-2-t-butylaminocarbonylpyrrolidine (1), (S)-1,2-(bis-t-butylaminocarbonyl)pyrrolidine (2), (S)-1-t-butylaminocarbonyl-2-(1-naphthylaminocarbonyl)pyrrolidine (3), (S)-1-t-butylaminocarbonyl-2(1-naphthylaminomethyl)pyrrolidine (4), (2S,4S)-1,2-(bis-t-butylaminocarbonyl)-4-aminopyrrolidine (5)) of general formula [Cu(CH3CN) (L-L)]X (X=PF6, ClO4) have been synthesised and fully characterised by elemental analysis, IR, electronic and NMR spectroscopy. These complexes catalyse the cyclopropanation of styrene, used as a model for monosubstituted olefins, with ethyl diazoacetate to yield a mixture of cis/trans ethyl 2-phenylcyclopropan-1-carboxylates with up to 30% ee.