Synthesis and Reversible Redox Properties of an Electron-Rich Polyferrocenylsilane with tert-Butyl Substituents on the Cyclopentadienyl Ligands

Abstract

The strained sila-[1]ferrocenophane monomer Fe(η-C5H3 t Bu)2SiPh2 (5) was synthesized and polymerized via thermal ring-opening polymerization (ROP) both in the melt and in solution to give the soluble high-molecular-weight polyferrocenylsilane (PFS) [Fe(η-C5H3 t Bu2)2SiPh2] n , 7 (M n = 5.2 × 104−1.7 × 106 Da, PDI = 1.38−1.99). Both monomer 5 and polymer 7 were structurally characterized by 1H, 13C, and 29Si NMR spectroscopy and elemental analysis. The electronic structure and electrochemical properties of the monomer 5 and the polymer 7 were investigated by UV−vis spectroscopy and cyclic voltammetry. The oxidation potentials were shifted to more negative values relative to non-methylated or methylated analogues, indicating that the electron-donating effect of the t Bu group is transmitted to the iron center. Polymer 7 exhibited two reversible redox waves with a redox coupling, ΔE 1/2, of 0.33 V, which is indicative of appreciable Fe···Fe interactions along the polymer backbone. The resiliency of 7 toward the redox processes was probed by measuring the molecular weights before photooxidation or chemical oxidation (with tetracyanoethylene (TCNE) or tris(4-bromophenyl)ammoniumyl hexachloroantimonate) and after subsequent reduction of the oxidized polymers to the neutral forms by using bis(pentamethylcyclopentadienyl)iron(II). Significantly, unlike the previous studies of oxidized PFS homopolymers, soluble polymeric salts were obtained even for a high degree of oxidation, and these were characterized by UV−vis and IR spectroscopy. GPC measurements demonstrated the excellent redox resiliency of polyferrocenylsilane 7 to redox cycling as no appreciable decline in molecular weight was apparent for degrees of oxidation of up to 50%.

Strained Metallocenophanes and Related Organometallic Rings Containing π‐Hydrocarbon Ligands and Transition‐Metal Centers

“…The actual ratio can be determined and ranges from 2 = 3 to 2 for different dilithioferrocenes. [13] 2.2.2. Group 13 Elements as Bridges Boron [14] The first reported boron-bridged ferrocenophanes 4 [15] prepared by Braunschweig and Manners [Eq.…”

“…For example, 13 [25] 1,1'-di(methylgallyl)ferrocene: d = 76.2 ppm [32] ). This upfield shift is characteristic of strained [n]metallocenophanes (for example, 4, C ipso : d = 44-45 ppm; [15] 1,2-bis(dimethylamino)-1,2-dibora[2]ferrocenophane, C ipso : d = 76.2 ppm [19] ).…”

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

“…77 Functional groups directly attached to the cyclopentadienyl rings are appealing as the redox properties of the iron centres can be directly influenced. In response to the above problems, successful functionalisation of the Cp groups of PFDMS was reported using low temperature metalation with t-BuLi/KOt-Bu in THF, followed by reaction with Me3SiCl.…”

“…Thus, the oxidation potentials of poly(tert-butylferrocenyldiphenylsilane) ( Figure 8) were more negative than those of the methylated or non-methylated analogues due to the electron donating effect of the tert-butyl group on the iron centre. 77 Substantial redox coupling (∆E1/2 = 0.33 V) was also detected. Significantly, the presence of tert-butyl groups markedly decreased the propensity for the polymer to undergo chain cleavage on oxidation.…”

“…77 As oxidised PFSs are generally insoluble in non-nucleophilic organic solvents these materials are difficult to process and study.…”