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Relativity as a Synthesis Design Principle: A Comparative Study of [3 + 2] Cycloaddition of Technetium(VII) and Rhenium(VII) Trioxo Complexes with Olefins


Braband, Henrik; Benz, Michael; Spingler, Bernhard; Conradie, Jeanet; Alberto, Roger; Ghosh, Abhik (2021). Relativity as a Synthesis Design Principle: A Comparative Study of [3 + 2] Cycloaddition of Technetium(VII) and Rhenium(VII) Trioxo Complexes with Olefins. Inorganic Chemistry, 60(15):11090-11097.

Abstract

The difference in [3 + 2] cycloaddition reactivity between fac-[MO3(tacn)]+ (M = Re, 99Tc; tacn = 1,4,7-triazacyclononane) complexes has been reexamined with a selection of unsaturated substrates including sodium 4-vinylbenzenesulfonate, norbornene, 2-butyne, and 2-methyl-3-butyn-2-ol (2MByOH). None of the substrates was found to react with the Re cation in water at room temperature, whereas the 99Tc reagent cleanly yielded the [3 + 2] cycloadducts. Interestingly, a bis-adduct was obtained as the sole product for 2MByOH, reflecting the high reactivity of a 99TcO-enediolato monoadduct. On the basis of scalar relativistic and nonrelativistic density functional theory calculations of the reaction pathways, the dramatic difference in reactivity between the two metals has now been substantially attributed to differences in relativistic effects, which are much larger for the 5d metal. Furthermore, scalar-relativistic ΔG values were found to decrease along the series propene > norbornene > 2-butyne > dimethylketene, indicating major variations in the thermodynamic driving force as a function of the unsaturated substrate. The suggestion is made that scalar-relativistic effects, consisting of greater destabilization of the valence electrons of the 5d elements compared with those of the 4d elements, be viewed as a new design principle for novel 99mTc/Re radiopharmaceuticals, as well as more generally in heavy-element coordination chemistry.

Abstract

The difference in [3 + 2] cycloaddition reactivity between fac-[MO3(tacn)]+ (M = Re, 99Tc; tacn = 1,4,7-triazacyclononane) complexes has been reexamined with a selection of unsaturated substrates including sodium 4-vinylbenzenesulfonate, norbornene, 2-butyne, and 2-methyl-3-butyn-2-ol (2MByOH). None of the substrates was found to react with the Re cation in water at room temperature, whereas the 99Tc reagent cleanly yielded the [3 + 2] cycloadducts. Interestingly, a bis-adduct was obtained as the sole product for 2MByOH, reflecting the high reactivity of a 99TcO-enediolato monoadduct. On the basis of scalar relativistic and nonrelativistic density functional theory calculations of the reaction pathways, the dramatic difference in reactivity between the two metals has now been substantially attributed to differences in relativistic effects, which are much larger for the 5d metal. Furthermore, scalar-relativistic ΔG values were found to decrease along the series propene > norbornene > 2-butyne > dimethylketene, indicating major variations in the thermodynamic driving force as a function of the unsaturated substrate. The suggestion is made that scalar-relativistic effects, consisting of greater destabilization of the valence electrons of the 5d elements compared with those of the 4d elements, be viewed as a new design principle for novel 99mTc/Re radiopharmaceuticals, as well as more generally in heavy-element coordination chemistry.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Scopus Subject Areas:Physical Sciences > Physical and Theoretical Chemistry
Physical Sciences > Inorganic Chemistry
Uncontrolled Keywords:Inorganic Chemistry, Physical and Theoretical Chemistry
Language:English
Date:2 August 2021
Deposited On:27 Aug 2021 15:09
Last Modified:01 Oct 2022 22:35
Publisher:American Chemical Society (ACS)
ISSN:0020-1669
OA Status:Hybrid
Free access at:PubMed ID. An embargo period may apply.
Publisher DOI:https://doi.org/10.1021/acs.inorgchem.1c00995
PubMed ID:34255507
Project Information:
  • : FunderSNSF
  • : Grant IDPZ00P2_126414
  • : Project TitleTechnetium Chemistry at High Oxidation States: New Perspectives for Nanomaterials and Polyoxometalates in Medicine and Environmental Science
  • : FunderFP7
  • : Grant ID262229
  • : Project TitleEuropean Plate Observing System
  • : FunderSouth African National Research Foundation
  • : Grant ID129270
  • : Project Title
  • : FunderSouth African National Research Foundation
  • : Grant ID132504
  • : Project Title

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