Chiral-at-Metal Racemization Unraveled for MX 2 (a-chel) 2 by means of a Computational Analysis of MoO 2 (acnac) 2

Octahedral chiral-at-metal complexes MX 2 (a-chel) 2 (a-chel=asymmetric chelate) can rearrange their ligands by four mechanisms known as the Bailar (B), Ray-Dutt (RD), Conte-Hippler (CH), and Dhimba-Muller-Lammertsma (DML) twists. Racemization involves their interconnections, which were computed for...

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Bibliographic Details
Published in:Chemistry – A European Journal
Main Authors: Dhimba, George, Muller, Alfred, Lammertsma, Koop
Format: Article in Journal/Newspaper
Language:English
Published: 2023
Subjects:
coordination modes
density functional calculations
homogeneous catalysis
molybdenum
N,O-ligands
DML
Online Access:https://research.vu.nl/en/publications/93fcd27f-5924-47ee-ba04-8512f76ffa6e
https://doi.org/10.1002/chem.202302516
https://hdl.handle.net/1871.1/93fcd27f-5924-47ee-ba04-8512f76ffa6e
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Description
Summary:Octahedral chiral-at-metal complexes MX 2 (a-chel) 2 (a-chel=asymmetric chelate) can rearrange their ligands by four mechanisms known as the Bailar (B), Ray-Dutt (RD), Conte-Hippler (CH), and Dhimba-Muller-Lammertsma (DML) twists. Racemization involves their interconnections, which were computed for MoO 2 (acnac) 2 (acnac=β-ketoiminate) using density functional theory at ωB97x-D with the 6-31G(d,p) and 6-311G(2d,p) basis sets and LANL2DZ for molybdenum. Racemizing the cis(NN) isomer, being the global energy minimum with trans oriented imine groups, is a three step process (DML-CH-DML) that requires 17.4 kcal/mol, while all three cis isomers (cis(NN), cis(NO), and cis(OO)) interconvert at ≤17.9 kcal/mol. The B and RD twists are energetically not competitive and neither are the trans isomers. The interconnection of all enantiomeric minima and transition structures is summarized in a graph that also visualizes valley ridge inflection points for two of the three CH twists. Geometrical features of the minima and twists are given. Lastly, the influence of N-substitution on the favored racemization pathway is evaluated. The present comprehensive study serves as a template for designing chiral-at-metal MX 2 (a-chel) 2 catalysts that may retain their chiral integrity.

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