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. 2025 Jul 14;64(27):13569-13576.
doi: 10.1021/acs.inorgchem.5c01280. Epub 2025 May 29.

Chiral-at-Tungsten Dioxo Complexes─A Computational Study on Inhibiting Racemization

George Dhimba  1 , Alfred Muller  1 , Koop Lammertsma  1   2
Affiliations

Chiral-at-Tungsten Dioxo Complexes─A Computational Study on Inhibiting Racemization

George Dhimba et al. Inorg Chem. .

Abstract

Chiral cis-WO2(acac)2 and cis-WO2(nacnac)2 complexes racemize via four pathways according to DFT calculations at ωB97X-D/6-311+G(2d,f) with LANL2DZ for W and with inclusion of acetonitrile solvent. Steric congestion by N-Me and N-Ph substitution of the two nacnac ligands has a substantial geometrical impact and raises the barriers for all pathways. Despite this, even all N-Me and all N-Ph substituted derivatives of cis-WO2(nacnac)2 have the same four channels for racemization. For each of these complexes, the Dhimba-Muller-Lammertsma (DML) twist is preferred over the Conte-Hippler (CH) twist and significantly favored over the established Bailar (B) and Ray-Dutt (RD) twists. The favored DML barrier for WO2(nacnac)2Ph4 has a large estimated ΔG barrier of 25.7 kcal/mol, suggesting it to be a viable chiral-at-tungsten complex for asymmetric catalysis.

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Figures

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(a) Bailar, (b) Ray-Dutt, (c) Conte-Hippler, and (d) Dhimba-Muller-Lammertsma twists by which chiral octahedral dioxo complexes undergo racemization. The bidentate ligands are shown in blue and green, and the two oxo ligands with a dashed line, colored red. The gray lines complement the edges of the octahedral and trigonal prismatic structures, with the dashed orange lines representing the transition metal coordination sites.
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Muetterties’ adapted topological representation of MX2(chel)2 with octahedral structures (open dots) and connecting trigonal prismatic ones (closed dots) shown separately with green curved lines for the chelates and labeled with the twist mechanism, B= Bailar, RD = Ray-Dutt, CH = Conte-Hippler, and DML = Dhimba-Muller-Lammertsma.
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WO2(acac)2 structures at ωB97X-D/6–31G­(d) and LANL2DZ for W.
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WO2(nacnac)2 structures at ωB97X-D/6–31G­(d) and LANL2DZ for W. Double-headed red arrows for CH and RD indicate close distances (in Å).
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WO2(nacnac)2 Me4 transition structures at ωB97X-D/6–31G­(d) and LANL2DZ for W.
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Space filling views of Δ-cis-WO2(nacnac)2 (top left), Δ-cis-WO2(nacnac)2 Me4 (top right), and the trans isomer (bottom).
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WO2(nacnac)2 Me4 structures for Δ, DML, and CH at ωB97X-D/6–31G­(d) and LANL2DZ for W. Hydrogen atoms are omitted for clarity.
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