Linear Oligo(ferrocenyldimethylsilanes) with between Two and Nine Ferrocene Units:  Electrochemical and Structural Models for Poly(ferrocenylsilane) High Polymers

Abstract

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...

Organometallic Ferrocene- and Phosphorus-Containing Polymers: Synthesis and Characterization

“…Manners and co-workers have developed ferrocene polymers with various bridging moieties in the main chains [29], and they found that silicon bridged ferrocene polymers have two redox peaks due to the strong metal-metal interaction [30]. It has been reported that the initial oxidation occurs at alternating iron sites and subsequent oxidation occurs at a higher potential due to the charge repulsion between the iron sites [31]. In addition, it was reported that doped ferrocene polymers possess semiconductor characteristics [32].…”

Photonic-crystal full-colour displays

“…A schematic of the cell is shown in Fig. 2a, and consists of the 17 . The cyclic voltammogram of this material (measured in a three-electrode configuration; Fig.…”

Synthesis and Solution Self‐Assembly of Polyisoprene‐block‐poly(ferrocenylmethylsilane): A Diblock Copolymer with an Atactic but Semicrystalline Core‐Forming Metalloblock

“…21,92,[111][112][113] This is indicative of a stepwise process where initial oxidation at alternating iron centres occurs, because as one iron centre is oxidised ( 1 E1/2), the neighbouring sites become more difficult to oxidise (Scheme 9). Thus a higher potential is required ( 2 E1/2), resulting in the two oxidation waves with redox coupling, ∆E1/2 = 2 E1/2 -1 E1/2 (≈ 250 mV for PFSs).…”

“…Thus a higher potential is required ( 2 E1/2), resulting in the two oxidation waves with redox coupling, ∆E1/2 = 2 E1/2 -1 E1/2 (≈ 250 mV for PFSs). 92 When identical experimental conditions are used for the electrochemical experiments (including the use of the same solvent and supporting electrolyte) the separation of the two waves, ∆E1/2, provides an approximate measure of the electronic interaction between iron centres along the polymer backbone. 114 Studies of isolated linear and cyclic oligomers has shown that the equal intensity, two redox-wave pattern characteristic of PFS materials corresponds to the limiting case of an infinite chain.…”

“…114 Studies of isolated linear and cyclic oligomers has shown that the equal intensity, two redox-wave pattern characteristic of PFS materials corresponds to the limiting case of an infinite chain. 65,92 Functionalisation of the Cp rings with electron donating groups lowers the oxidation potential of the ferrocene center in the neutral species. For example the cyclic voltammetric halfwave oxidation potentials of PFS are reduced by ca.…”