Synthesis, Electrochemical Behavior, and Self-Assembly of Metallocene-Functionalized Thiolluorenes

With a view to preparing organometallics for the fabrication of self-assembled monolayers (SAMs) and their possible electrochemical applications, we report the synthesis and characterization of ferrocene- and ruthenocene-functionalized thiofluorenes 4b and 6b, respectively. These sandwich compounds were accessible through a consecutive synthesis methodology. 9,9-Dimethyl-2,7-diiodofluorene (1) with tBuLi, S-8, and Me(CO)C1 gave 9,9-dimethyl-2-iodo-7-thioacetyl-fluorene (2), which, with Mc-C -CH [3: Mc = (eta(5)-C5H4)(eta(5)-C5H5)Fe (Fc); 5: Mc = (eta(5)-C5H4)(eta(5)-C5H5)Ru (Rc)] following the Sonogashira C-C cross-coupling protocol, produced the corresponding metal alkynyl-fluorenes Mc-C C-9,9-FluMe(2)-SC(O)CH3 (4a: Mc = Fc; 6a: Mc = Rc; Flu = fluorenyl). Addition of NH4OH/HCl gave thiols Mc-C C-9,9-FluMe(2)-SH (4b: Mc = Fc; 6b: Mc = Rc). Compounds 4b, 6b, and the related precursors were characterized electrochemically by cyclic voltammetry (CV). For comparison, the CV data of several biphenyl analogues of 4b and 6b are also reported and thus the oxidation processes of the Fc, Re, and sulfur units have been studied. The ability of 4b and 6b to form SAMS was demonstrated by the fabrication of such films on Au(111) substrates. These films were subsequently characterized by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The spectroscopic data for the 4b/Au and 6b/Au films suggest the formation of contaminant-free SAMs with relatively high packing density (2.0 x 10(14) and 2.2 X 10(14) molecules/cm(2), respectively).