(1,1′-Ferrocenediyl)ferrocenyl(methyl)silane, Its Thermally Ring-Opened Polymer, and Oligomer Models

Abstract

The synthesis and spectroscopic and structural characterization of a ferrocenyl-substituted silyl-[1]-ferrocenophane, (1,1′-ferrocenediyl)ferrocenyl(methyl)silane, 1, is reported. 1 crystallizes in space group P21/c, with a = 20.344(8) Å, b = 7.336(3) Å, c = 11.567(7) Å, and β = 90.51(4)°. The dihedral angles between the two ferrocenophane cyclopentadienyl rings are 21.3°, and the ring centroid—Fe—ring centroid angle is 164.3°. Cyclic voltammetric analysis illustrates that both of the Fe centers, ferrocenyl and ferrocenophane, exhibit reversible redox behavior. This reversibility distinguishes the complex from other [1]-ferrocenophanes which exhibit irreversible oxidation under similar conditions. Thermal treatment of 1 results in facile polymerization to high molecular weight amorphous poly(ferrocenyleneferrocenyl- (metbyl)silane), 2. The molecular weight of the polymer was considerably increased by performing the polymerization in solution as opposed to the melt, Mw = 210 000 vs 45 000. The electrochemical properties of the polymer indicate that neighboring Fe centers of the ferrocenylenesilane chain and pendant ferrocenyl groups interact, and four independent redox processes are observed. As a model for the ferrocenylenedialkylsilane polymers the synthesis and X-ray structure of 1,1′-bis(ferrocenyldimethylsilyl)ferrocene, 3, is also reported. 3 crystallizes in space group P21/c, with a = 10.084(2) Å, b = 14.958(2) Å, c = 11.175(2) Å, and β = 114.98(1)°. The ferrocenyl and ferrocenylene units are perpendicular to each other, and each of the Fe units exhibits an individual redox process upon cyclic voltammetric investigation. Molecular mechanics calculations reveal a range of structures with local energy minima for such oligomers, one of which is equivalent to the single-crystal X-ray structure obtained for 3. The Fe—Fe distances in these conformers differ significantly, 6.1–6.9 Å, suggesting that high molecular weight polymers also possess a range of possible conformations and inter-Fe Coulombic interactions. © 1994, American Chemical Society. All rights reserved.