Synthesis, Crystal Structures, and Electrochemical Behavior of Fe-Ru Heterobimetallic Complexes with Bridged Metallocene Units
Abstract
A series of Fe-Ru complexes was prepared by reactions of (2-phenylethyl)ferrocene, (E)-(2-phenylethenyl)ferrocene, and (phenylethynyl)ferrocene with [Ru(eta(5)-C5R5)(MeCN)3][PF6] (R = H, Me) salts. These heterobimetallic complexes of the general formula [Fc-spacer-(eta(6)-C6H5)Ru(eta(5)-C5R5)][PF6] (Fc = ferrocenyl, spacer = CH2CH2 (4), CH=CH (5), CC (6)) were isolated as hexafluorophosphate salts and characterized by elemental analysis, NMR spectroscopy, and ESI MS.
The structures of the complete series of [Fc-spacer-(eta(6)-C6H5)Ru(eta(5)-C5Me5)]Cl and of [FcC CRu(eta(6)-C6H5)(eta(5)-C5H5)][PF6] were determined by X-ray diffraction analysis. In addition, a cyclobutadiene complex [Ru(eta(5)-C5H5)(eta(4)-1,2-Fc2-3,4-Ph2C4)][PF6] (7[PF6]), obtained along with some unidentified alkyne oligomers and 6a[PF6] upon the treatment of 3 with [Ru(eta(5)-C5H5)(MeCN)3][PF6], was characterized similarly, including structure determination.
Cyclic voltammetry measurements performed on the precursor Fc-spacer-Ph revealed that these compounds undergo a single reversible one-electron oxidation, which can be attributed to the ferrocene/ferrocenium redox couple. Their redox potential increases with increasing electron-withdrawing nature of the ferrocenyl substituent (Eo: 1 < 2 < 3).
The cationic Fe Ru complexes show similar redox waves that are shifted to more positive potential due to coordination of the positively charged Ru(eta(5)-C5R5) fragment and are only marginally influenced by the substitution at the Ru-bonded cyclopentadienyl ring (C5H5 vs C5Me5). Furthermore, the metal-organic Fe-Ru dyads exert an irreversible reduction event below 2 V presumably due to reduction of the Ru center.
Spectroelectrochemical measurements in the UV-vis-NIR region and DFT computations confirmed the anticipated nature of the observed oxidative redox processes and further suggested electronic communication between the metal centers in compounds possessing the conjugated linking groups.