Chiral Tricationic Tris(1,2-diphenylethylenediamine) Cobalt(III) Hydrogen Bond Donor Catalysts with Defined Carbon/Metal Configurations; Matched/Mismatched Effects upon Enantioselectivities with Enantiomeric Chiral Counter Anions

Abstract

The enantiopure and diastereopure salts Λor Δ-[Co((S,S)-dpen) 3 ] 3+ 2Cl − BAr f − (Λ-or Δ-(S,S)-1 3+ 2Cl − BAr f − ; dpen/BAr f = 1,2-diphenylethylenediamine/B(3,5-C 6 H 3 (CF 3 ) 2 ) 4 ) and Λ-(S,S)-1 3+ 3Cl − are treated with salts of the enantiopure chiral monoanions (A − ) or dianions (A 2− ) 3-bromocamphor-8sulfonate (camphSO 3 − ), 1,1′-binaphthyl-2,2′-diyl phosphate (and three 3,3′-disubstituted derivatives), a related biphenanthryl species, tartrate, and Sb 2 (tart′− , and Λ-(S,S)-1 3+ 3A − are isolated as hydrates and characterized by NMR and microanalyses. In the presence of tertiary amines, many of these are highly enantioselective catalysts for additions of 1,3-dicarbonyl compounds to trans-β-nitrostyrene and di-tert-butylazodicarboxylate. The ee values for diastereomeric salts can exhibit significant differences (avg/high/median Δ %ee = 10/63/6; matched/mismatched effect), and in a few cases, they are better than those obtained with Λor Δ-(S,S)-1 3+ 2Cl − BAr f − . The crystal structure of Δ-(S,S)-1 3+ 2(1S)-camphSO 3 − BAr f − shows that the two sulfonate moieties hydrogen-bond to opposite (idealized) C 3 -symmetric faces of the trication, with a separate oxygen atom associated with each of the three synperiplanar NH groups.

Recent Developments in Enantioselective Transition Metal Catalysis Featuring Attractive Noncovalent Interactions between Ligand and Substrate

“…In 2020, the same authors reported an interesting study involving the combination of the chiral [Co(( S,S )-dpen) 3 ] 3+ cations with chiral monoanions or dianions. 67 These diastereomeric salts could catalyze the addition of 1,3-dicarbonyl compounds to trans -β-nitrostyrene and di- tert -butylazodicarboxylate with significant variation in enantioselectivity, although the performances of the matched catalysts only occasionally exceeded those from their report in 2015. Recently, the same authors have also investigated a range of lipophilic [M(en) 3 ] n+ [BAr F 4 ] − salts with a variety of metal centers.…”

Enantioselective “organocatalysis in disguise” by the ligand sphere of chiral metal-templated complexes

“…2). 91,109,116,117,124,132,133,136 It was proven by single crystal X-ray crystallographic analysis that the counter anions formed multidentate hydrogen bonds with the amino groups of the cobalt(III) complexes. 155,156 Evidently, the Brønsted acidity of the NH 2 groups was enhanced significantly.…”

“…2 'Werner-type' chiral octahedral cobalt(III) complexes as asymmetric hydrogen bond donor catalysts. 91,109,116,117,124,132,133,136 Scheme 1 Enantioselective Michael addition of dimethyl malonate to cyclopentenone catalysed by the chiral 'Werner-type' cobalt(III) complex D-1 (Gladysz, 2008). 91 The products were obtained with very high enantioselectivities (up to 499% ee) and excellent yields (up to 99%) (Scheme 3).…”

“…1a and c), greatly increases as compared to the original non-coordinated form. 91,95,98,105,109,[116][117][118]132,136 Gladysz nicknamed these chiral systems chiral ''organocatalysts in disguise''. [84][85][86][87] Structurally, the metal serves either as a template (a purely structural role) (Fig.…”

Preparation of Optically Pure Dinuclear Cobalt(III) Complex with Λ-Configuration as a Dianionic Chiral Catalyst

“…The absolute configuration of the cobalt metal centers is determined to be Λ based on the starting materials (R)-3, (S)-4, and the Flack parameter [0.015(5)] 12 obtained via the X-ray crystallographic analysis (Figure 2). 13 Recently, chiral cobalt(III) complexes have been recognized as highly enantioselective anionic catalysts 14 for Michael reaction, 15,16 halocyclization, 7,17 Mannich reaction, 18 and Povarov reaction. 19,20 We also carried out preliminary screening for the catalytic activity of the dimeric Λ-cobalt(III) complex 1 in the enantioselective bromocyclization of tryptamine derivative 6.…”