TY - JOUR
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 - 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 - N,O-ligands
KW - coordination modes
KW - density functional calculations
KW - homogeneous catalysis
KW - molybdenum
UR - http://www.scopus.com/inward/record.url?scp=85175064798&partnerID=8YFLogxK
U2 - 10.1002/chem.202302516
DO - 10.1002/chem.202302516
M3 - Article
AN - SCOPUS:85175064798
SN - 0947-6539
VL - 29
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 66
M1 - e202302516
ER -