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Polysiloxanes Bearing Pendant Redox-Active Dendritic Wedges Containing Ferrocenyl and (η6-Aryl)tricarbonylchromium Moieties

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journal contribution
posted on 25.10.2011, 00:00 by Magdalena Zamora, Sonia Bruña, Beatriz Alonso, Isabel Cuadrado
Novel highly functionalized polysiloxanes have been synthesized, which bear small pendant dendritic wedges containing two different redox-active organometallic moieties, namely the electron-donating ferrocenyl group and the electron withdrawing (η6-aryl)tricarbonylchromium entity. Hydrosilylations of vinylsilyl-functionalized (CH2CH)MePhSiFc (1) and allylsilyl-terminated dendron (CH2CHCH2)PhSi[(CH2)2MePhSiFc]2 (3), with the Si–H-containing polysiloxane backbones (Me3SiO)(MeSiHO)n(Me2SiO)m(SiMe3) (n = 30–35%, m = 65–70%), and (Me3SiO)(MeSiHO)n(SiMe3) (n ∼ 35) successfully afforded the novel siloxane-based copolymers 8 and 9 and homopolysiloxanes 10 and 11 possessing appended organometallic dendritic side chains. Thermal treatment of 8 with Cr(CO)6 and reaction of 10 with (CH3CN)3Cr(CO)3 further increased metal density of the polymers affording polysiloxanes 12 and 13 carrying (η5-C5H4)Fe(η5-C5H5) and (η6-C6H5)Cr(CO)3 moieties hanging from their polysiloxane chain. Similar reactions, starting from 1,1,3,3-tetramethyldisiloxane and phenyltris(dimethylsiloxy)silane, were also a convenient way to prepare the corresponding homo and heterometallic model compounds [MePhFcSi(CH2)2Me2Si]2O (5), [{(η6-C6H5)Cr(CO)3}MeFcSi(CH2)2Me2Si]2O (6), and PhSi[OMe2Si(CH2)2MePhSiFc]3 (7). These model compounds and the metallopolysiloxanes were characterized by IR, multinuclear NMR spectroscopies and mass spectrometry. Thermogravimetric analysis (TGA) established that dendronized polysiloxanes 9 and 11, with ferrocenyl dendrons derived from 3, possess higher thermal stability than parent ferrocenyl polysiloxanes 8 and 10. Ferrocenyl dendronized polysiloxanes 9 and 11 yield ceramic products, which have been characterized by SEM and EDX microanalyses. Solution electrochemical studies showed that all the ferrocenyl units present in polysiloxanes 813 are electrochemically independent. Ferrocenyl polysiloxanes 811, deposited electroactive films onto electrode surfaces. Their well-defined and persistent redox waves are characteristic of electrochemically stable, surface-confined reversible redox couples.