Chiral-at-Metal Racemization Unraveled for MX2(a-chel)2 by means of a Computational Analysis of MoO2(acnac)2

George Dhimba; Alfred Muller; Koop Lammertsma

doi:10.1002/chem.202302516

Chiral-at-Metal Racemization Unraveled for MX₂(a-chel)₂ by means of a Computational Analysis of MoO₂(acnac)₂

George Dhimba, Alfred Muller, Koop Lammertsma^*

^*Corresponding author for this work

Research output: Contribution to Journal › Article › Academic › peer-review

Abstract

Octahedral chiral-at-metal complexes MX₂(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 MoO₂(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 MX₂(a-chel)₂ catalysts that may retain their chiral integrity.

Original language	English
Article number	e202302516
Pages (from-to)	1-8
Number of pages	8
Journal	Chemistry - A European Journal
Volume	29
Issue number	66
Early online date	20 Sept 2023
DOIs	https://doi.org/10.1002/chem.202302516
Publication status	Published - 24 Nov 2023

Bibliographical note

Funding Information:
We gratefully acknowledge the support of the National Research Foundation (Grant 120842) and the Centre for High Performance Computing (CHPC) of South Africa.

Publisher Copyright:
© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.

Funding

We gratefully acknowledge the support of the National Research Foundation (Grant 120842) and the Centre for High Performance Computing (CHPC) of South Africa.

Keywords

coordination modes
density functional calculations
homogeneous catalysis
molybdenum
N,O-ligands

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10.1002/chem.202302516

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Cite this

@article{93fcd27f592447eeba048512f76ffa6e,

title = "Chiral-at-Metal Racemization Unraveled for MX2(a-chel)2 by means of a Computational Analysis of MoO2(acnac)2",

abstract = "Octahedral chiral-at-metal complexes MX2(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 MoO2(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 MX2(a-chel)2 catalysts that may retain their chiral integrity.",

keywords = "coordination modes, density functional calculations, homogeneous catalysis, molybdenum, N,O-ligands",

author = "George Dhimba and Alfred Muller and Koop Lammertsma",

note = "Funding Information: We gratefully acknowledge the support of the National Research Foundation (Grant 120842) and the Centre for High Performance Computing (CHPC) of South Africa. Publisher Copyright: {\textcopyright} 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.",

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T1 - Chiral-at-Metal Racemization Unraveled for MX2(a-chel)2 by means of a Computational Analysis of MoO2(acnac)2

AU - Dhimba, George

AU - Muller, Alfred

AU - Lammertsma, Koop

N1 - Funding Information: We gratefully acknowledge the support of the National Research Foundation (Grant 120842) and the Centre for High Performance Computing (CHPC) of South Africa. Publisher Copyright: © 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.

PY - 2023/11/24

Y1 - 2023/11/24

N2 - Octahedral chiral-at-metal complexes MX2(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 MoO2(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 MX2(a-chel)2 catalysts that may retain their chiral integrity.

AB - Octahedral chiral-at-metal complexes MX2(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 MoO2(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 MX2(a-chel)2 catalysts that may retain their chiral integrity.

KW - coordination modes

KW - density functional calculations

KW - homogeneous catalysis

KW - molybdenum

KW - N,O-ligands

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