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

摘要

The synthesis of mono- and difunctionalized [Re(eta(6)-C6H5R)(eta(6)-C6H6-n R-n)](+) (n = 0, 1; R = COOH, Br) complexes starting from [Re(eta(6)-benzene)(2)](+) is described. The lithiation of [Re(eta(6)-benzene)(2)](+) with n-BuLi leads preferentially to the neutral, alkylated product [Re(eta(6)-C6H6)(eta(5)-C6H6-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(eta(6)-C6H5Br)(eta(6)-C6H6)](+), [Re(eta(6)-C6H5Br)(2)](+), or [Re(eta(6-)-C6H5COOH)(eta(6)-C6H6)](+), [Re(eta(6)-C6H5COOH)(2)](+). These functionalized derivatives of [Re(eta(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(eta(6)-C6H5R)(eta(6)-C6H6-nRn)](+) (n = 0, 1; R= -SCH2Ph, -NHPh, -CONHCH2Ph, C6H5-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 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.