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 sp2 in the free ligand to sp3 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