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(κ 1 P-alkene)(κ 2 P-alkene)] and cis -[Rh(κ 2 P-alkene) 2 ][BF 4 ], 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(κ 1 P-alkene) 2 ] and [Cu(κ 1 P-alkene) 2 BF 4 ], 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(C 2 H 5 ) 3 to 2-cyclohexenone with 39% ee.
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Drinkel et al. (2010) studied this question.