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. 2021 Oct 13;143(40):16709-16717.
doi: 10.1021/jacs.1c07857. Epub 2021 Oct 4.

Understanding Halide Counterion Effects in Enantioselective Ruthenium-Catalyzed Carbonyl (α-Aryl)allylation: Alkynes as Latent Allenes and Trifluoroethanol-Enhanced Turnover in The Conversion of Ethanol to Higher Alcohols via Hydrogen Auto-transfer

Eliezer Ortiz  1 , Jonathan Z Shezaf  1 , Yu-Hsiang Chang  1 , Théo P Gonçalves  2 , Kuo-Wei Huang  2 , Michael J Krische  1
Affiliations

Understanding Halide Counterion Effects in Enantioselective Ruthenium-Catalyzed Carbonyl (α-Aryl)allylation: Alkynes as Latent Allenes and Trifluoroethanol-Enhanced Turnover in The Conversion of Ethanol to Higher Alcohols via Hydrogen Auto-transfer

Eliezer Ortiz et al. J Am Chem Soc. .

Abstract

Crystallographic characterization of RuX(CO)(η3-C3H5)(JOSIPHOS), where X = Cl, Br, or I, reveals a halide-dependent diastereomeric preference that defines metal-centered stereogenicity and, therefrom, the enantioselectivity of C-C coupling in ruthenium-catalyzed anti-diastereo- and enantioselective C-C couplings of primary alcohols with 1-aryl-1-propynes to form products of carbonyl anti-(α-aryl)allylation. Computational studies reveal that a non-classical hydrogen bond between iodide and the aldehyde formyl CH bond stabilizes the favored transition state for carbonyl addition. An improved catalytic system enabling previously unattainable transformations was developed that employs an iodide-containing precatalyst, RuI(CO)3(η3-C3H5), in combination with trifluoroethanol, as illustrated by the first enantioselective ruthenium-catalyzed C-C couplings of ethanol to form higher alcohols.

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Figures

Figure 1.
Figure 1.
Halide effects in enantioselective ruthenium-catalyzed conversion of ethanol to higher alcohols.
Figure 2.
Figure 2.
Solid state structures of RuX(CO)(JOSIPHOS)(η3-C3H5), where X = Cl, Br, I, as determined by single crystal X-ray diffraction and selected bond distances. Disorder due to incomplete axial site selectivity between the CO ligand and halide counterion is evident for the complexes containing chloride and bromide but not iodide. Displacement ellipsoids are scaled to the 50% probability level. Hydrogen atoms have been omitted for clarity.a a See Supporting Information for complete crystallographic data
Figure 3.
Figure 3.
Gradient trajectories mapped on a total electron density plot in the Ru-I-HCO plane showing bond critical points (BCP, blue circles).
Scheme 1.
Scheme 1.
Chair-like transition structures leading to enantiomeric products of carbonyl anti-(α-aryl)allylation (ΔΔG‡ in kcal/mol at ωB97X-V).
Scheme 2.
Scheme 2.
Proposed catalytic cycle and stereochemical model for the ruthenium-catalyzed C-C coupling of 1-aryl-1-propynes with ethanol to form products of carbonyl anti-(α-aryl)allylation.
See this image and copyright information in PMC

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