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Cis- and trans molybdenum oxo complexes of a prochiral tetradentate aminophenolate ligand : Synthesis, characterization and oxotransfer activity

Hossain, Md Kamal LU ; Köhntopp, Anja ; Haukka, Matti ; Richmond, Michael G. ; Lehtonen, Ari and Nordlander, Ebbe LU (2020) In Polyhedron 178.
Abstract

Reaction of [MoO2Cl2(dmso)2] with the tetradentate O2N2 donor ligand papy [H2papy = N-(2-hydroxybenzyl)-N-(2-picolyl)glycine] leads to formation of the dioxomolybdenum(VI) complex [MoO2(papy)] (1) as a mixture of cis and trans isomers. Recrystallization from methanol furnishes solid cis-1, whereas the use of a dichloromethane-hexane mixture allows for the isolation of the trans-1 isomer. Both isomers have been structurally characterized by X-ray crystallography and the energy difference between the isomeric pair has been investigated by electronic structure calculations. Optimization of two configurational isomers in the gas phase predicts the trans isomer to... (More)

Reaction of [MoO2Cl2(dmso)2] with the tetradentate O2N2 donor ligand papy [H2papy = N-(2-hydroxybenzyl)-N-(2-picolyl)glycine] leads to formation of the dioxomolybdenum(VI) complex [MoO2(papy)] (1) as a mixture of cis and trans isomers. Recrystallization from methanol furnishes solid cis-1, whereas the use of a dichloromethane-hexane mixture allows for the isolation of the trans-1 isomer. Both isomers have been structurally characterized by X-ray crystallography and the energy difference between the isomeric pair has been investigated by electronic structure calculations. Optimization of two configurational isomers in the gas phase predicts the trans isomer to lie 2.5 kcal/mol lower in energy (ΔG) than the cis isomer, which is inconsistent with the solution NMR data in d3-MeCN that exhibit a Keq of ca. 3 at 298 K for the trans ⇌ cis equilibrium. The DFT-computed energy difference is significantly improved (Keq = 5.4) by the inclusion of the MeCN solvent using the polarization continuum model (PCM). Density functional calculations reveal that the isomerization proceeds via a Ray-Dutt twist mechanism with a barrier of 14.5 kcal/mol, which is in accordance with the 1H NMR spectral data and the rapid equilibration of these isomers in solution. The catalytic reactivity of [MoO2(papy)] in the epoxidation of cis-cyclooctene is described, as well as its ability to effect oxo transfer from DMSO to PPh3.

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author
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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Computational modelling, Epoxidation, Oxo Atom Transfer, Tripodal ligand, Variable temperature NMR
in
Polyhedron
volume
178
article number
114312
publisher
Elsevier
external identifiers
  • scopus:85077925786
ISSN
0277-5387
DOI
10.1016/j.poly.2019.114312
language
English
LU publication?
yes
id
131ead54-6bf3-4495-bb08-e62918f2f090
date added to LUP
2020-01-30 17:41:57
date last changed
2020-02-12 10:20:14
@article{131ead54-6bf3-4495-bb08-e62918f2f090,
  abstract     = {<p>Reaction of [MoO<sub>2</sub>Cl<sub>2</sub>(dmso)<sub>2</sub>] with the tetradentate O<sub>2</sub>N<sub>2</sub> donor ligand papy [H<sub>2</sub>papy = N-(2-hydroxybenzyl)-N-(2-picolyl)glycine] leads to formation of the dioxomolybdenum(VI) complex [MoO<sub>2</sub>(papy)] (1) as a mixture of cis and trans isomers. Recrystallization from methanol furnishes solid cis-1, whereas the use of a dichloromethane-hexane mixture allows for the isolation of the trans-1 isomer. Both isomers have been structurally characterized by X-ray crystallography and the energy difference between the isomeric pair has been investigated by electronic structure calculations. Optimization of two configurational isomers in the gas phase predicts the trans isomer to lie 2.5 kcal/mol lower in energy (ΔG) than the cis isomer, which is inconsistent with the solution NMR data in d<sub>3</sub>-MeCN that exhibit a K<sub>eq</sub> of ca. 3 at 298 K for the trans ⇌ cis equilibrium. The DFT-computed energy difference is significantly improved (K<sub>eq</sub> = 5.4) by the inclusion of the MeCN solvent using the polarization continuum model (PCM). Density functional calculations reveal that the isomerization proceeds via a Ray-Dutt twist mechanism with a barrier of 14.5 kcal/mol, which is in accordance with the <sup>1</sup>H NMR spectral data and the rapid equilibration of these isomers in solution. The catalytic reactivity of [MoO<sub>2</sub>(papy)] in the epoxidation of cis-cyclooctene is described, as well as its ability to effect oxo transfer from DMSO to PPh<sub>3</sub>.</p>},
  author       = {Hossain, Md Kamal and Köhntopp, Anja and Haukka, Matti and Richmond, Michael G. and Lehtonen, Ari and Nordlander, Ebbe},
  issn         = {0277-5387},
  language     = {eng},
  month        = {03},
  publisher    = {Elsevier},
  series       = {Polyhedron},
  title        = {Cis- and trans molybdenum oxo complexes of a prochiral tetradentate aminophenolate ligand : Synthesis, characterization and oxotransfer activity},
  url          = {http://dx.doi.org/10.1016/j.poly.2019.114312},
  doi          = {10.1016/j.poly.2019.114312},
  volume       = {178},
  year         = {2020},
}