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

Abstract

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 (η 6 -aryl)tricarbonylchromium entity. Hydrosilylations of vinylsilyl-functionalized (CH 2 ═CH)MePhSiFc ( 1 ) and allylsilyl-terminated dendron (CH 2 ═CHCH 2 )PhSi[(CH 2 ) 2 MePhSiFc] 2 ( 3 ), with the Si–H-containing polysiloxane backbones (Me 3 SiO)(MeSiHO) n (Me 2 SiO) m (SiMe 3 ) ( n = 30–35%, m = 65–70%), and (Me 3 SiO)(MeSiHO) n (SiMe 3 ) ( 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 (CH 3 CN) 3 Cr(CO) 3 further increased metal density of the polymers affording polysiloxanes 12 and 13 carrying (η 5 -C 5 H 4 )Fe(η 5 -C 5 H 5 ) and (η 6 -C 6 H 5 )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(CH 2 ) 2 Me 2 Si] 2 O ( 5 ), [{(η 6 -C 6 H 5 )Cr(CO) 3 }MeFcSi(CH 2 ) 2 Me 2 Si] 2 O ( 6 ), and PhSi[OMe 2 Si(CH 2 ) 2 MePhSiFc] 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 8 – 13 are electrochemically independent. Ferrocenyl polysiloxanes 8 – 11, deposited electroactive films onto electrode surfaces. Their well-defined and persistent redox waves are characteristic of electrochemically stable, surface-confined reversible redox couples.