In order to gain insight into the electrochemical and conformational properties of the prototypical high polymeric poly(ferrocenylsilane), poly(ferrocenyldimethylsilane) [Fe(η-C5H4)2SiMe2] n 6, three series of oligo(ferrocenylsilanes) R-fc-[SiMe2-fc] n - 1-R‘ (fc = Fe(η-C5H4)2) 7 2 −7 9 (R = R‘ = H), 8 2 −8 7 (R = H and R‘ = SiMe3), and 9 2 −9 7 (R = R‘ = SiMe3) have been prepared and studied (the subscript n in the oligomer refers to the number of ferrocene units present). These species were prepared via the anionic ring-opening oligomerization of the silicon-bridged [1]ferrocenophane Fe(η-C5H4)2SiMe2 5. Initiation with ferrocenyllithium FcLi (Fc = Fe(η-C5H5)(η-C5H4)) followed by quenching with H2O or SiMe3Cl afforded H-fc-[SiMe2-fc] n - 1-H (7 2 -9 ) or H-fc-[SiMe2-fc] n - 1-SiMe3 (8 2 -7 ), respectively. Initiation with the dilithioferrocene complex fcLi·2/3TMEDA followed by quenching with H2O or SiMe3Cl similarly afforded the oligomers H-fc-[SiMe2-fc] n - 1-H (7 2 -9 ) or alternatively the bis(silyl)-capped species Me3Si-fc-[SiMe2-fc] n - 1-SiMe3 (9 2 -7 ), respectively. The individual molecular compounds of these three series of oligomers 7 2 −7 9 , 8 2 −8 7 , and 9 2 −9 7 were isolated in pure form from the oligomeric mixtures by column chromatography and these were structurally characterized by 1H, 13C, and 29Si NMR spectroscopy, mass spectrometry, and in selected cases by elemental analysis. The structure of the linear pentamer 7 5 has also been determined by single crystal X-ray diffraction. The central portion of this species possesses a trans planar zigzag conformation in the solid state and appears to be a valuable model for the analogous conformation of the high polymer 6 in crystalline domains. The electrochemical behavior of each pure oligomer was studied by cyclic and differential pulse voltammetry and was found to depend on whether an odd or an even number of ferrocene units were present. For oligomer systems containing an odd number of iron centers two reversible redox processes of varying intensities at −0.02−0.00 V and 0.21−0.23 V (vs ferrocene) were observed with a redox splitting of 0.21−0.23 V. For oligomer systems containing an even number of iron centers larger then two, three reversible redox processes of varying intensities were observed at ca. 0.00, 0.13, and 0.24 V vs ferrocene. As the oligomer chain length increased, the electrochemical behavior for both the “odd” and “even” series approached that of the high polymer 6 for which two reversible redox processes at 0.00 and 0.24 V (vs ferrocene) of equal intensity exist. These results are completely consistent with the previously proposed theory that initial oxidation of 6 affords a product in which alternating iron sites are oxidized. Spectroelectrochemical experiments show an intervalence electron transfer absorption (1100−1350 nm, εmax ⩽ 150 M-1 cm-1) for partially oxidized oligo(ferrocenylsilanes) that is typical for class II mixed-valent compounds. Additionally, single crystals were obtained of the m...

The oxidative electron-transfer properties of several superphane complexes consisting of cyclopentadienylcobalt cyclobutadiene moieties linked by either three (compounds 1 and 4) or five (compounds 2 and 5) bridging methylene groups have been studied by experimental and theoretical methods. In both cases two separate one-electron oxidations are found. The mixed-valent monocations of the (−CH2−)5-bridged complexes are valence-trapped with very weak interactions between metal centers. The (−CH2−)3 complexes, however, have strong interactions between the two molecular halves. The intervalence transfer (IT) band of 1 + has characteristics of both class II (localized) and class III (delocalized) behavior, but the IR spectra of carboxy-labeled 4 + clearly establish trapped valence for the monocations of the propano-bridged systems. Photoelectron spectra and ab initio calculations at the UHF level show that, in the ground electronic state, 1 + has a half-filled orbital (i.e., electron spin) that is essentially localized in one Co d xy , orbital, but that the charges on the two metals are unequal owing to inductive electronic effects which give unequal electron flow from the ligands to the two metal centers. Calculations and IR (carbonyl) spectral shifts suggest about a 70:30 charge ratio between the two metal centers in 1 + and 4 +, whereas both spin and charge localization is virtually complete in the pentano-bridged complexes 2 + and 5 +. The intervalence transition in 1 + is proposed to proceed through a “hole”-transfer process mediated by a π-cyclobutadiene MO, ultimately involving a through-bond transannular mechanism.

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