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

Abstract

AbstractReactions of RhCl3 and (S,S)‐1,2‐diphenylethylenediamine (S,S‐dpen) in DMSO at 140 °C give Λ‐[Rh(S,S‐dpen)3]3+3Cl− (Λ‐(S,S)‐43+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 Λ‐(S,S)‐43+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 °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 C3 face of Λ‐(S,S)‐43+, which features three synperiplanar NH groups. Λ‐(S,S)‐43+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).