Bis-Arene Complexes [Re(η 6 -arene) 2 ] + as Highly Stable Bioorganometallic Scaffolds.

The synthesis of mono- and difunctionalized [Re(η6 -C6 H5 R)(η6 -C6 H6-n Rn )]+ (n = 0, 1; R = COOH, Br) complexes starting from [Re(η6 -benzene)2 ]+ is described. The lithiation of [Re(η6 -benzene)2 ]+ with n-BuLi leads preferentially to the neutral, alkylated product [Re(η6 -C6 H6 )(η5 -C6 H6 -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-tetra-bromoethane (TBE) or with CO2 , respectively, gave [Re(η6 -C6 H5 Br)(η6 -C6 H6 )]+ , [Re(η6 -C6 H5 Br)2 ]+ , or [Re(η6 -C6 H5 COOH)(η6 -C6 H6 )]+ , [Re(η6 -C6 H5 COOH)2 ]+ . These functionalized derivatives of [Re(η6 -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(η6 -C6 H5 R)(η6 -C6 H6-n Rn )]+ (n = 0, 1; R = -SCH2 Ph, -NHPh, -CONHCH2 Ph, -C6 H5 -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, the1 H 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.