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Bis-Arene Complexes [Re($η^6$-arene)$_2$]$^+$ as Highly Stable Bioorganometallic Scaffolds


Meola, Giuseppe; Braband, Henrik; Schmutz, Paul; Benz, Michael; Spingler, Bernhard; Alberto, Roger (2016). Bis-Arene Complexes [Re($η^6$-arene)$_2$]$^+$ as Highly Stable Bioorganometallic Scaffolds. Inorganic Chemistry, 55(21):11131-11139.

Abstract

The synthesis of mono- and difunctionalized [Re($η^6$-C$_6$H$_5$R)($η^6$-C$_6$H$_{6−n}$R$_n$)]$^+$ (n = 0, 1; R = COOH, Br) complexes starting from [Re($η^6$-benzene)$_2$]$^+$ is described. The lithiation of [Re($η^6$-benzene)$_2$]$^+$ with n-BuLi leads preferentially to the neutral, alkylated product [Re($η^6$-C$_6$H$_6$)($η^5$-C$_6$H$_6$-Bu)] but not to the expected deprotonation of the arene ring. Deprotonation/lithiation with LDA gave the mono- and the dilithiated products in situ. Their reactions with 1,1,2,2-tetrabromoethane (TBE) or with CO$_2$, respectively, gave [Re($η^6$-C$_6$H$_5$Br)($η^6$-C$^6$H$^6$)]$^+$, [Re($η^6$-C$_6$H$_5$Br)$_2$]$^+$, or [Re($η^6$-C$_6$H$_5$COOH)($η^6$-C$_6$H$_6$)]$^+$, [Re($η^6$-C$_6$H$_5$COOH)$_2$]$^+$. These functionalized derivatives of [Re($η^6$-benzene)$_2$]+ represent novel precursors for the synthesis of bioconjugates to bioactive structures, comparable to [Co(Cp)$_2$]$^+$ or [Fe(Cp)$_2$]. Different model compounds [Re($η^6$-C$_6$H$_5$R)($η^6$-C$_6$H$_{6−n}$R$_$n)]$^+$ (n = 0, 1; R = −SCH$_2$Ph, −NHPh, −CONHCH$_2$Ph, −C$_6$H$_5$-COdpa) were synthesized via amide bond formation and nucleophilic aromatic substitution. These conjugates were fully characterized including X-ray structure analyses of most products. For all complexes, the 1H NMR arene proton signals are strongly upfield-shifted as compared to those of the noncoordinated arenes. The electrochemical analyses show an irreversible, probably substituent-centered oxidation, which contrasts the cyclic voltammetry of the underivatized complexes where oxidation is fully reversible. The stability of the core and the reactivity of the substituents make these bis-arene complexes useful precursors in medicinal inorganic chemistry, comparable to cobaltocenium or ferrocene.

Abstract

The synthesis of mono- and difunctionalized [Re($η^6$-C$_6$H$_5$R)($η^6$-C$_6$H$_{6−n}$R$_n$)]$^+$ (n = 0, 1; R = COOH, Br) complexes starting from [Re($η^6$-benzene)$_2$]$^+$ is described. The lithiation of [Re($η^6$-benzene)$_2$]$^+$ with n-BuLi leads preferentially to the neutral, alkylated product [Re($η^6$-C$_6$H$_6$)($η^5$-C$_6$H$_6$-Bu)] but not to the expected deprotonation of the arene ring. Deprotonation/lithiation with LDA gave the mono- and the dilithiated products in situ. Their reactions with 1,1,2,2-tetrabromoethane (TBE) or with CO$_2$, respectively, gave [Re($η^6$-C$_6$H$_5$Br)($η^6$-C$^6$H$^6$)]$^+$, [Re($η^6$-C$_6$H$_5$Br)$_2$]$^+$, or [Re($η^6$-C$_6$H$_5$COOH)($η^6$-C$_6$H$_6$)]$^+$, [Re($η^6$-C$_6$H$_5$COOH)$_2$]$^+$. These functionalized derivatives of [Re($η^6$-benzene)$_2$]+ represent novel precursors for the synthesis of bioconjugates to bioactive structures, comparable to [Co(Cp)$_2$]$^+$ or [Fe(Cp)$_2$]. Different model compounds [Re($η^6$-C$_6$H$_5$R)($η^6$-C$_6$H$_{6−n}$R$_$n)]$^+$ (n = 0, 1; R = −SCH$_2$Ph, −NHPh, −CONHCH$_2$Ph, −C$_6$H$_5$-COdpa) were synthesized via amide bond formation and nucleophilic aromatic substitution. These conjugates were fully characterized including X-ray structure analyses of most products. For all complexes, the 1H NMR arene proton signals are strongly upfield-shifted as compared to those of the noncoordinated arenes. The electrochemical analyses show an irreversible, probably substituent-centered oxidation, which contrasts the cyclic voltammetry of the underivatized complexes where oxidation is fully reversible. The stability of the core and the reactivity of the substituents make these bis-arene complexes useful precursors in medicinal inorganic chemistry, comparable to cobaltocenium or ferrocene.

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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
Language:English
Date:12 October 2016
Deposited On:03 Feb 2017 10:32
Last Modified:04 Feb 2017 08:46
Publisher:American Chemical Society (ACS)
ISSN:0020-1669
Publisher DOI:https://doi.org/10.1021/acs.inorgchem.6b01748
PubMed ID:27731624

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