Bile Acid DerivedTropos VaultedBi­naphth­ylphosphites: Synthesis, Stereo­chemical Characterization and Complexation to Rhodium

Three different 2,2′-binaphthylphosphites were synthesized, starting from suitable derivatives of cholic or deoxycholic acids and 1,1′-dihydroxy-2,2′-binaphthyl, and their stereochemical features were analyzed by CD and NMR spectroscopy. The spectroscopic data clearly demonstrate the capability of the cholestanic backbone to induce a M prevalent screw sense to the flexible binaphthyl moiety, giving rise to tropos ligands. The extent of the prevalence of the M sense of twist depends on the position at which the binaphthylphosphite moiety is linked on the bile acid skeleton. The three phosphites were mixed with [Rh(COD)2][BF4] and the resulting complexes were analyzed by variable temperature 31P NMR spectroscopy, thereby obtaining information on their stereochemical characteristics, which reflect the different asymmetric induction capability of the ligands.