Asymmetric Activation of the Pd Catalyst Bearing the Tropos Biphenylphosphine (BIPHEP) Ligand with the Chiral Diaminobinaphthyl (DABN) Activator¹

Abstract

[reaction: see text] The enantio- and diastereomerically pure Pd complex of the tropos biphenylphosphine (BIPHEP) ligand is obtained through complexation of the enantiopure (R)-diaminobinaphthyl (DABN) with either enantiomer of the BIPHEP-Pd catalyst, followed by tropo-inversion of the less favorable (S)-BIPHEP-Pd/(R)-DABN diastereomer to the more favorable (R)-BIPHEP-Pd/(R)-DABN diastereomer. The enantiopure BIPHEP-Pd catalyst with DABN affords higher enantioselectivity and catalytic efficiency as an activated Lewis acid catalyst than the enantiopure BIPHEP-Pd catalyst without DABN.

Resolution of BIPHEP on Rh with a chiral diene auxiliary

“…Mikami has performed dynamic resolutions of BIPHEP on Ru [28,29], Pd [30,31], and most recently Rh [32] with the use of enantiopure chiral diamine ligands. As the barriers to atropisomerization are generally higher when BIPHEP is complexed to a transition metal, these complexes can sometimes be used for asymmetric catalysis without significant erosion of the enantiopurity of the catalyst.…”

Solution Structure and Behavior of Benzophenone‐based Achiral Bisphosphine Ligands in Noyori‐Type Ru(II)‐Catalysts

“…Table 1 lists the NMR spectral assignment for the major resonances of (S)-3a (Scheme 3) in toluene-d 8 as determined from DQF-COSY, HMQC, and 1 H-15 N HSQC NMR data analysis. Importantly, 31 P NMR spectra show a distinct pair of doublets with a J P-P value of 23.0 Hz. This is in contrast to the expected singlet resonance observed in 31 P NMR of RuCl 2 -complexes which show a representative "doubling-up" for each resonance due to the C 2 symmetry of the trans dichloride configuration.…”

“…Due to the facial ligand arrangement, and the fact that NH-protons within each group belong to different N-atoms (H5 ax , H2 eq or H2 ax , H5 eq , determined by DQF-COSY) the complex must adopt a single configuration with magnetically (and chemically) distinct upper and lower parts about the plane defined by P,P-Ru-N,N. Importantly, 31 P and 1 H VT-NMR analysis of 3a conducted in toluene-d 8 show no significant structural change throughout the temperature range of 10-70 ℃ (Figure 1b). The observed solution structure is thus stable and not fluxional, in contrast to the behavior of the free component ligand 4.…”

Active Pd(II) Complexes as Either Lewis Acid Catalysts or Transition Metal Catalysts

“…The diastereomeric mixture of 57/(R)-DABN can exhibit tropo inversion of the BIPHEP-Pd moiety at 80°C to afford favorable (R)-57/(R)-DABN exclusively. The single diastereomer (R)-57/(R)-DABN prepared via tropo inversion can be used as an activated chiral catalyst for the hetero Diels-Alder (HDA) reaction of glyoxylate 51, leading to significantly higher chemical yields and enantioselectivity (Scheme 41) [182]. The efficiency of (R)-DABN as a chiral activator is highlighted by the higher levels of enantioselectivity and catalytic activity than those (11%, 75% ee) attained by using the enantiopure (R)-57 without (R)-DABN.…”