Rhodium(III) Werner Complexes with 1,2-Diphenylethylenediamine Ligands: Syntheses, Structures, and Applications as Chiral Hydrogen Bond Donor Catalysts and Agents for Enantiomer Purity Determinations

Reactions of RhCl3 and (S,S)-1,2-diphenylethylenediamine (S,S-dpen) in DMSO at 140 degrees C give Lambda-[Rh(S,S-dpen)(3)](3+)3Cl(-) (Lambda-(S,S)-4(3+)3Cl(-)) in 76 % yield. When CH2Cl2/water suspensions are treated with 1.0 equiv. of Na+ B(C6F5)(4)(-) or Na+ B(3,5-C6H3(CF3)(2))(4)(-), the mixed salts Lambda-(S,S)-4(3+)2Cl(-)B(aryl)(4)(-) can be isolated from the organic layers (95-91 %). A wide variety of mixed and non-mixed salts involving these and other anions (BF4-, ClO4-, I-) are also prepared. The lipophilic salts are highly enantioselective catalysts for the Michael addition of dimethylmalonate to trans-ss-nitrostyrene (acetone, 0 degrees C; 92-85 % ee). The crystal structures of seven solvated salts are determined, and hydrogen bonding between the trications and anions or solvate molecules analyzed. There is a notable affinity of chloride anions for the C-3 face of Lambda-(S,S)-4(3+), which features three synperiplanar NH groups. Lambda-(S,S)-4(3+)2I(-)B(C6F5)(4)(-) is an excellent chiral solvating agent for determining enantiomeric purities of chiral organic molecules with hydrogen bond accepting functional groups (11 mol% (average), CDCl3).

Automated summary

The reaction of RhCl3 and (S,S)-1,2-diphenylethylenediamine (S,S-dpen) in DMSO at 140 degrees C yielded Lambda-[Rh(S,S-dpen)(3)](3+)3Cl(-) (Lambda-(S,S)-4(3+)3Cl(-)) in 76% yield. Various mixed and non-mixed salts involving different anions were prepared, and their crystal structures and hydrogen bonding were analyzed. The lipophilic salts showed high enantioselectivity as catalysts for the Michael addition reaction of dimethylmalonate to trans-ss-nitrostyrene.