Asymmetric synthesis of cyanohydrins catalysed by a potassium Δ-bis[N-salicylidene-(R)-tryptophanato]cobaltate complex

Belokon, Y. N.; Bulychev, A. G.; Maleev, Victor I.; North, Michael; Malfanov, Ilya L.; Ikonnikov, N. S.

doi:10.1070/mc2004v014n06abeh002029

Cited by 36 publications

(21 citation statements)

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“…The catalytic cycle shown in Scheme 4w as supported by 1 HNMR data of complexes 1 and 3 in CDCl 3 before (Figure3a and 4a)a nd after (Figure 3b and 4b)a ddition of ten equivalents of propylene oxide.T he salient feature of the initial spectra was the very significant difference in the chemical shifts of the two diastereotopic hydrogens comprising the NH 2 groups of the ligands. One reason for this was as ignificant magnetic anisotropic screening of the pro-R hydrogen atom by the C=N bond of the neighboring ligand ( Figure 2), movingi ts resonance to higherf ields (around 2-3 ppm).…”

Section: Resultsmentioning

confidence: 61%

“…Recently, we introduced a new class of stereochemically inert coordinatively saturated chiral complexes of cobalt(III) as promoters of asymmetric carbon–carbon bond forming reactions . The use of chiral octahedral complexes, where the metal ion is not involved in the catalytic act and only serves to position and activate organic groups of a ligand, is a fast evolving new field of research .…”

Section: Introductionmentioning

confidence: 99%

“…Recently,w ei ntroduced an ew class of stereochemically inert coordinatively saturated chiral complexes of cobalt(III) as promoters of asymmetricc arbon-carbon bond forming reactions. [1][2][3][4][5][6] The use of chiral octahedral complexes, where the metal ion is not involved in the catalytic act and only serves to positiona nd activate organic groups of al igand,i safast evolvingn ew field of research. [7][8][9][10][11][12][13][14][15] An efficient group of such catalysts developed by our group are cationic complexes of cobalt(III) and Schiff bases obtained from substituted salicylic aldehydes and (R,R)-or (S,S)-cyclohexane diamine (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Chiral Cobalt(III) Complexes as Bifunctional Brønsted Acid–Lewis Base Catalysts for the Preparation of Cyclic Organic Carbonates

et al. 2015

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Stereochemically inert cationic cobalt(III) complexes were shown to be one-component catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide at 50 °C and 5 MPa carbon dioxide pressure. The optimal catalyst possessed an iodide counter anion and could be recycled. A catalytic cycle is proposed in which the ligand of the cobalt complexes acts as a hydrogen-bond donor, activating the epoxide towards ring opening by the halide anion and activating the carbon dioxide for subsequent reaction with the halo-alkoxide. No kinetic resolution was observed when terminal epoxides were used as substrates, but chalcone oxide underwent kinetic resolution.

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Section: Resultsmentioning

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Chiral Cobalt(III) Complexes as Bifunctional Brønsted Acid–Lewis Base Catalysts for the Preparation of Cyclic Organic Carbonates

et al. 2015

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confidence: 99%

Chiral‐at‐Metal Octahedral Iridium Catalyst for the Asymmetric Construction of an All‐Carbon Quaternary Stereocenter

et al. 2013

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Asymmetric catalysts, whether metal complexes with chiral ligands, chiral organometallics, or chiral organic compounds (organocatalysts), achieve asymmetric induction by transferring chiral information from the catalyst to the substrate(s). [1] The source of the catalysts chirality therefore plays a crucial role for its mode of action, and is typically derived from one or more tetrahedral stereogenic centers (mostly carbon atoms, but also heteroatoms, such as sulfur or phosphorus), axial chirality, planar chirality, or a combination thereof (Scheme 1). In contrast, only few reports exist of asymmetric catalysts that derive their chirality exclusively from an octahedral stereocenter. [2][3][4] This seems surprising, considering the prevalence of the octahedral coordination geometry in chemistry and its ability to support the generation of structures with high complexity and, as a result of ligand crowding and chelate effects, often low conformational flexibility. [5] We recently demonstrated the use of chiral-atmetal octahedral complexes for the tailored design of a highly efficient asymmetric noncovalent catalyst that requires low catalyst loading by reporting an inert iridium(III)-based catalyst for the conjugate asymmetric transfer hydrogenation of b,b-disubstituted nitroalkenes. [6] However, excellent metal-, bio-, and organo-catalysts already exist for this transformation, [7] and we were therefore wondering whether an octahedral chiral-at-metal catalyst could be developed for a more challenging asymmetric conversion. In this respect, the asymmetric conjugate addition of carbon nucleophiles to b,b-disubstituted nitroalkenes constitutes a highly attractive reaction as it permits the construction of a stereogenic carbon atom bound to four other carbon substituents (all-carbon quaternary stereocenter). [8] Only a handful of studies are available dealing with this particular reaction, thereby presumably reflecting the involved challenge of overcoming a significant steric repulsion between the incoming carbon nucleophile and the carbon substituents of the nitroalkene electrophile. Nevertheless, Hoveyda and co-workers introduced a Cu-catalyzed dialkylzinc conjugate addition, [9] Arai and co-workers reported a Cu-catalyzed addition of indoles to isatin-derived nitroalkenes, [10] Jia and co-workers disclosed a Ni-catalyzed addition of indoles to b-CF 3 -b-disubstituted nitroalkenes, [11] Ricci and co-workers reported a phase-transfer asymmetric organocatalytic conjugate addition of cyanide to b,b-disubstituted nitroalkenes, albeit with only modest enantioselectivities, [12] Melchiorre and co-workers introduced the asymmetric vinylogous Michael addition of cyclic enones to nitroalkenes catalyzed by natural cinchona alkaloids, including one reaction using a b,b-disubstituted nitroalkene, [13] and finally Kastl and Wennemers introduced a proline-peptide-catalyzed asymmetric addition of aldehydes to b,b-disubstituted nitroalkenes under formation of g-nitroaldehydes. [14] The restricted scope of dialkylzinc reagents and t...

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“…We recently introduced octahedral chiral-at-metal [22][23][24][25][26][27][28][29][30][31][32][33][34][35] iridium(III) complexes as inert templates for the design of lowloading asymmetric hydrogen bonding catalysts 36,37 . Octahedral stereocenter [38][39][40] permit the straightforward generation of compounds with high shape and stereochemical complexity and should therefore be highly suitable as structural templates for multifunctional catalysts.…”

mentioning

confidence: 99%

Metal-templated chiral Brønsted base organocatalysis

Ding

et al. 2014

Nat Commun

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Inert octahedral chiral-at-metal complexes are an emerging class of asymmetric catalysts that exploit the globular, rigid nature and stereochemical options of octahedral compounds. While the central transition metal serves as a structural anchorpoint and provides metal centrochirality, catalysis is mediated through the organic ligand sphere, thereby merging the branches of transition metal catalysis and organocatalysis. Here we report the development of inert octahedral 3-aminopyrazolato iridium(III) complexes as novel chiral Brønsted base catalysts and demonstrate their merit with applications to highly effective asymmetric sulfaMichael and aza-Henry reactions, permitting catalyst loadings down to 0.02 and 0.25 mol%, respectively. The observed high stereocontrol can be rationalized by a bifunctional mode of action in which the iridium catalyst, after the initial proton transfer, controls a ternary complex through defined hydrogen bonding interactions. This work reveals the potential of octahedral metal complexes as chiral scaffolds for the design of high-performance asymmetric catalysts.

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Asymmetric synthesis of cyanohydrins catalysed by a potassium Δ-bis[N-salicylidene-(R)-tryptophanato]cobaltate complex

Cited by 36 publications

References 2 publications

Chiral Cobalt(III) Complexes as Bifunctional Brønsted Acid–Lewis Base Catalysts for the Preparation of Cyclic Organic Carbonates

Chiral Cobalt(III) Complexes as Bifunctional Brønsted Acid–Lewis Base Catalysts for the Preparation of Cyclic Organic Carbonates

Chiral‐at‐Metal Octahedral Iridium Catalyst for the Asymmetric Construction of an All‐Carbon Quaternary Stereocenter

Metal-templated chiral Brønsted base organocatalysis

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