Hemilabile P-Alkene Ligands in Chiral Rhodium and Copper Complexes: Catalytic Asymmetric 1,4 Additions to Enones. 2^,

Abstract

Two equivalents of the chiral dibenz[b,f]azepine-derived P-alkene ligands 2−6 per metal afforded mononuclear Rh(I) and Cu(I) complexes that were used as catalysts for asymmetric conjugate addition reactions. Rh formed square-planar neutral (8−10) and cationic complexes (11, 12) of the general formulas [RhCl(κ1P-alkene)(κ2P-alkene)] and cis-[Rh(κ2P-alkene)2][BF4], respectively (P-alkene = 2, 5, 6). In both cases reversible decoordination of the alkene function of the bidentate P-alkene ligands was observed in the presence of Lewis basic solvents, and model compounds of mono- and bis-solvated species (13, 14) were isolated. Cu formed trigonal-planar neutral (15−17) and cationic complexes (18, 19) of the general formulas [CuI(κ1P-alkene)2] and [Cu(κ1P-alkene)2BF4], respectively (P-alkene = 2, 4, 5). The cationic Rh species 11 catalyzed the 1,4-addition of arylboronic acids to cyclic and linear enones with high activities (TON = 62 at 40 °C) and excellent enantiocontrol (up to 99% ee) for a wide range of substrates. The cationic Cu complex 18 catalyzed the 1,4-addition of Al(C2H5)3 to 2-cyclohexenone with 39% ee.