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

Reactions 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).

Post-Modification of Octahedral Chiral-at-Metal Cobalt(III) Complexes by Suzuki–Miyaura Cross-Coupling and Evaluation of Their Catalytic Activity

“…Recently, we introduced the well-defined stereochemically inert octahedral chiral-at-metal Co(III) complexes based on Schiff bases of the enantiopure 1,2-cyclohexanediamine (CHD) or 1,2-diphenylethylenediamine (dPhED) and salicylaldehydes as efficient metal-templated hydrogen bond donor (HBD) catalysts for various asymmetric transformations . On the other hand, the Gladysz and Meggers groups independently have developed chiral-at-metal cobalt(III)- and iridium(III)-templated HBDs, which have efficiently catalyzed a broad range of asymmetric reactions. , In these complexes a metal center mainly serves as an activator of the coordinated ligands (NH 2 groups) increasing their HBD ability, as well as a source of chirality (metal-centered chirality). , The configurations are designated according to the mutual arrangement of tridentate ligands around the cobalt ion: Λ (a left-handed propeller) and Δ (a right-handed propeller) configurations (see Figure ). Although the Suzuki–Miyaura CCRs have already been established as a method to modify Ir(III) complexes, ,, we did not find examples in the literature where enantiomerically pure Co(III) complexes were subjected to direct postmodification via CCRs.…”

Enantioselective Syntheses of Multiply Functionalized Six‐Membered Carbocycles from Nitroalkenes and γ,δ‐Unsaturated ß‐Ketoesters using Chiral Catalysts Derived from Cobalt(III) and 1,2‐Diphenylethylenediamine

“…Given the enormous variety of hydrogen bonding motifs that have been established by crystallographic and spectroscopic experiments for the cobalt(III) catalysts in Figure 1, [13] any proposed transition state is highly speculative. In previous papers, we have offered the occasional cartoon to rationalize the dominant enantiomer produced, [6a,7d,29] but none of these are compelling. As noted in the introduction, often one of the two Co/C diastereomers is more effective for one reaction, but the opposite diastereomer for another.…”

“…The remaining two chloride anions strongly hydrogen bond to the two C 3 symmetric faces, each of which has three synperiplanar NH bonds. The rhodium analog of Λ‐( S , S )‐ 1 3+ 2Cl − BAr f − has been crystallographically characterized [7d] …”