Chiral Dibenzazepine-Based P-Alkene Ligands and Their Rhodium Complexes: Catalytic Asymmetric 1,4 Additions to Enones

N -Dichlorophosphanyldibenzo[ b, f ]azepine ( 6 ) reacted with (−)-2,3- O -isopropylidene- d -threitol, ( R )-taddol, ( R,R )-diethyltartrate, ( R,R )-diethyltartrate, ( S )-binaphthol, α,α-diphenyl- l -prolinol, and ( S )-proline to form the corresponding chiral P-alkene ligands 7 − 12 . These ligands were then used to synthesize dinuclear chloro-bridged Rh(I) complexes 13 − 18 with the general formula [Rh(μ-Cl)(P-alkene)] 2 . It was shown by X-ray diffraction analyses that these P-alkenes indeed act as bidentate ligands for Rh(I). Furthermore, the crystal structures revealed a change in the hybridization state of the dibenzazepine N atom, passing from sp 2 in the free ligand to sp 3 when coordinated to Rh in a bidentate fashion, thus modifying the bite angle of the ligands. The Rh complexes 16 and 18, bearing the ( S )-binaphthol-derived ligand 10 and the α,α-diphenyl- l -prolinol-derived ligand 12, respectively, were shown to be active and enantioselective catalysts for the 1,4 addition of arylboronic acids to enones. At 80 °C turnover numbers of up to 61 and enantiomeric excesses of up to 92% were observed.