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

Abstract 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 com...

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Bibliographic Details
Published in:Chemistry – A European Journal
Main Authors: Dhimba, George, Muller, Alfred, Lammertsma, Koop
Other Authors: National Research Foundation
Format: Article in Journal/Newspaper
Language:English
Published: Wiley 2023
Subjects:
DML
Online Access:http://dx.doi.org/10.1002/chem.202302516
Description
Summary:Abstract 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.