Chiral ion pairs in catalysis: lithium salts of chiral metallocomplex anions as catalysts for asymmetric C–C bond formation

A series of Co(III) anionic complexes of Schiff bases obtained from substituted salicylaldehydes and optically active amino acids has been synthesized. The ion pairing of these anions to a lithium cation can be used to induce asymmetry into lithium-catalyzed trimethylsilylcyanation of aldehydes and Michael reactions. The influence of the temperature, solvent polarity and structural modification of the chiral anion on the enantioselectivity of the catalysis has been investigated.

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Lithium Λ-bis[N-salicylidene-(S)-valinato]cobaltateC24H26N2O6CoLiee >99%[α]D25=-4031 (c 0.032, MeOH)Source of chirality: synthesis from (S)-valineAbsolute configuration: Λ, (S,S)

Lithium Δ-bis[N-salicylidene-(S)-valinato]cobaltateC24H26N2O6CoLiee >99%[α]D25=-8631 (c 0.032, MeOH)Source of chirality: synthesis from (S)-valineAbsolute configuration: Δ, (S,S)

Lithium Λ-bis[N-(3-methoxysalicylidene)-(S)-valinato]cobaltateC26H30N2O8CoLiee >99%[α]D25=-3458 (c 0.031, MeOH)Source of chirality: synthesis from (S)-valineAbsolute configuration: Λ, (S,S)

Lithium Δ-bis[N-(3-methoxysalicylidene)-(S)-valinato]cobaltateC26H30N2O8CoLiee >99%[α]D25=-6982 (c 0.034, MeOH)Source of chirality: synthesis from (S)-valineAbsolute configuration: Δ, (S,S)

Lithium Λ-bis[N-(3-methoxysalicylidene)-(S)-tertleucinato]cobaltateC28H34N2O8CoLiee >99%[α]D25=-4500 (c 0.027, MeOH)Source of chirality: synthesis from (S)-tertleucineAbsolute configuration: Λ, (S,S)

Lithium Δ-bis[N-(3-methoxysalicylidene)-(S)-tertleucinato]cobaltateC28H34N2O8CoLiee >99%[α]D25=-5763 (с 0.027, MeOH)Source of chirality: synthesis from (S)-tertleucineAbsolute configuration: Δ, (S,S)

Lithium Λ-bis[N-(3-allylsalicylidene)-(S)-valinato]cobaltateC30H34N2O6CoLiee >99%[α]D25=-4633 (c 0.06, MeOH)Source of chirality: synthesis from (S)-valineAbsolute configuration: Λ, (S,S)

Lithium Δ-bis[N-(3-allylsalicylidene)-(S)-valinato]cobaltateC30H34N2O6CoLiee >99%[α]D25=-732 (c 0.044, MeOH)Source of chirality: synthesis from (S)-valineAbsolute configuration: Δ, (S,S)

Sodium Λ-bis[N-(3-methoxysalicylidene)-(S)-valinato]cobaltateC26H30N2O8CoNaee >99%[α]D25=-3697 (c 0.035, MeOH)Source of chirality: synthesis from (S)-valineAbsolute configuration: Λ, (S,S)

Sodium Δ-bis[N-(3-methoxysalicylidene)-(S)-valinato]cobaltateC26H30N2O8CoNaee >99%[α]D25=-8046 (c 0.035, MeOH)Source of chirality: synthesis from (S)-valineAbsolute configuration: Δ, (S,S)