Chiral Cobalt(III) Tris(1,2-diamine) Catalysts That Incorporate Nitrogenous Base Containing Anions for the Bifunctional Activation of Nucleophiles and Electrophiles in Enantioselective Addition Reactions
journal contributionposted on 11.06.2021, 20:05 by Connor Kabes, Reagan Lucas, Jack Gunn, John Gladysz
The lipophilic diastereomeric cobalt complexes Λ or Δ-[Co((S,S)-dpen)3]3+ 2Cl–BArf– (Λ or Δ-(S,S)-23+ 2Cl–BArf–; dpen/BArf– = 1,2-diphenylethylenediamine/B(3,5-C6H3(CF3)2)4–) catalyze a number of enantioselective C–H bond addition reactions in the presence of aliphatic tertiary amines, but pyridine and N,N-dimethylaniline are much less effective. However, when these bases are incorporated into counter anions (4–) as in Λ or Δ-(S,S)-23+ 4–Cl–BArf–, highly enantioselective bifunctional catalysts can be realized. Salts of nicotinates, isonicotinates, related sulfonates, and N,N-dimethylaminobenzoate are effective. The 6-chloronicotinate salt gives slower rates and lower ee values, and the 6-aminonicotinate salt gives faster rates and higher ee values. The 6-methyl, 2-methoxy, and unsubstituted analogs afford intermediate results. The 6-aminonicotinate catalyst is applied to additions of dimethyl malonate to 14 aryl-substituted nitroolefins and additions of 6 1,3-dicarbonyl compounds to di-t-butyl azodicarboxylate, with average yields/ee values of 90%/85% and 94%/77%, respectively. The authors are unaware of other ionic catalysts for which Brønsted bases have been productively incorporated into the anions, which are seldom if ever purposefully functionalized in any manner.