The potential of vinylferrocene Fc(CHCH 2 ) (1) as redox-active ene functional precursor for thiol−ene radical reaction has been successfully investigated for the first time. To this end, we initially studied thiol−ene model reactions of 1 with a variety of functionalized monothiols, including 2-mercaptoethanol, 1-thioglycerol, 3-mercaptopropionic acid, (3-mercaptopropyl)-trimethoxysilane, 2-aminoethanethiol hydrochloride, dithiol 2,2′-(ethylenedioxy)diethanethiol, and the tetrafunctional thiol pentaerythritol tetrakis(3-mercaptopropionate) (PETMP). These reactions afforded the newly ferrocenyl-hydrothiolated smallmolecule models Fc(CH 2 ) 2 S(CH 2 ) 2 OH (2), Fc(CH 2 ) 2 S(CH 2 ) 2 COOH (3), Fc(CH 2 ) 2 S(CH 2 )CH(OH)(CH 2 )OH (4), Fc(CH 2 ) 2 S(CH 2 ) 3 Si(OMe) 3 (5), bimetallic Fc(CH 2 ) 2 S(CH 2 ) 2 O(CH 2 ) 2 O(CH 2 ) 2 S(CH 2 ) 2 Fc (6), and tetrametallic [Fc(CH 2 ) 2 S-(CH 2 ) 2 COOCH 2 ] 4 C (7) in relatively high yields. Furthermore, the hydrothiolation of the CC bond of vinylferrocene was successfully extended to the S−H-polyfunctionalized poly[(3-mercaptopropyl)methylsiloxane] (PMMS), which provided access to a new redox-active polysiloxane (Me 3 SiO){MeSi[(CH 2 ) 3 S(CH 2 ) 2 Fc]O} n (SiMe 3 ) (8) containing covalently attached electroactive ferrocenyl−thioether side groups. The thiol−vinylferrocene reactions have been initiated either thermally, in toluene solution with AIBN, or by UV light irradiation in THF in the presence of 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator. The outcomes of the hydrothiolation of vinylferrocene strongly depend on the thiol structure and on the experimental conditions. Thermogravimetric analysis (TGA) of 8 established that the incorporation of pendant thioether− ferrocenyl units within the Si−O−Si backbone significantly improves the thermal stability of polymethylsiloxane in comparison to the S−H-polyfunctionalized PMMS precursor. Electrochemical studies revealed that polysiloxane 8, containing sulfur-bridged ferrocenyl moieties attached along the main chain, exhibits unusual and excellent adsorption properties and spontaneously forms robust films on Pt and Au electrodes. The well-defined and persistent voltammetric waves of the surface-adsorbed 8 films display nearly ideal redox behavior and exhibit peak potential separations (ΔE peak ) and full width at half-maximum (E fwhm ) values close to those theoretically expected for stable, surface-immobilized electroactive layers.

The application of ethynylferrocene, FcCCH (1), as a highly efficient electroactive precursor for the thiol–yne click reaction is presented. For this purpose, a wide range of functionalized thiols, namely 2-mercaptoethanol, 1-thioglycerol, 3-mercaptopropionic acid, 4-aminothiophenol, and benzene-1,3-dithiol as well as tetrathiol pentaerythritol tetrakis(3-mercaptopropionate), were investigated. This facile thiol–ethynylferrocene radical reaction has resulted in the quantitative formation and isolation of the newly ferrocenyl–vinyl sulfides FcCHCHS(CH2)2OH (2 Z and 2 E ), FcCHCHSCH2CH(OH)CH2OH (3 Z and 3 E ), FcCHCHS(CH2)2COOH (4 Z and 4 E ), FcC(CH2)S(1,4-C6H4)NH2 (5α), FcCHCHS(1,3-C6H4)SCHCHFc (6), and [FcCHCHS(CH2)2COOCH2]4C (7). Thiol–ethynylferrocene reactions have been initiated either by heat, in toluene with AIBN, or by UV light irradiation in THF in the presence of DMPA as photoinitiator. The outcome of the hydrothiolation of ethynylferrocene strongly depends on the thiol structure and on the initiation method employed. A simple mixing of metallocene 1 with the thiol HS(CH2)2OH or HS(CH2)2COOH in a proper ratio, in THF at 20 °C, in a initiator-free thiol–yne reaction, causes hydrothiolation of 1 to occur, allowing for the formation of vinyl sulfides 2 Z , 2 E and 4 Z , 4 E in good isolated yields. In contrast to the bis-addition typically observed for thiol–yne reactions, no double hydrothiolation to FcCCH has been observed for any of the thiols under any conditions studied. Electrochemical studies showed that tetrametallic compound 7, containing four sulfur-bridged ferrocenyl–vinyl moieties, behaves as a tetrapodal adsorbate molecule, exhibiting excellent chemisorption properties, and spontaneously forms robustly adsorbed 7 films onto Au or Pt electrode surfaces.

The application of 1,3-divinyl-1,3-dimethyl-1,3-diferrocenyldisiloxane [(CH 2 CH)FcMeSi] 2 O (1) as an efficient electroactive vinylsilane precursor for thiol−ene radical reactions is described. In order to determine if steric or electronic limitations due to the redox-active metallocene moiety might affect the bis(hydrothiolation) of the bifunctional vinylsilane, a model reaction was initially performed between 1 and 2-mercaptoethanol, resulting in the formation of the newly sulfur-containing carbosiloxane 2 in excellent yield. The bis(thiol−ene) reaction of 1 was successfully extended to 2,2′-(ethylenedioxy)diethanethiol, affording a series of novel precisely defined, redox-active oxathiacrown macrocycles (3 and 4 n ) and sulfur-bearing linear oligo-carbosiloxanes (5 n and 6 n ) with a backbone in which the −S(CH 2 ) 2 −O(CH 2 ) 2 O−(CH 2 ) 2 S− chain and the −Si−O−Si− bond, bearing pendant ferrocenes, are alternately linked by ethylene bridges. These reactions have been initiated either thermally (in toluene solution with AIBN) or by UV light irradiation in THF in the presence of 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator, even though UV photoinitiated thiol−ene reactions were found to be the most efficient hydrothiolations. All newly silicon-containing oxathioether-based ferrocenyl compounds 2−6 n have been thoroughly characterized using a combination of elemental analysis, multinuclear NMR spectroscopy, FT-IR, and MALDI-TOF mass spectrometry to establish their chemical structures and chain-end functionalities. The electrochemical behavior of 2−6 n has been examined by cyclic and square wave voltammetries, in dichloromethane solution using [PF 6 ] − and [B(C 6 F 5 ) 4 ] − as supporting electrolyte anions of different coordinating ability. The sulfur-rich cyclic and linear oligomers 4 n −6 n exhibit excellent chemisorption properties and spontaneously form robustly adsorbed electroactive films onto Au or Pt electrode surfaces. The cation complexation ability of diferrocenyl silaoxathiacrown ether 3 has been studied using electrochemical and 1 H NMR spectroscopic techniques. The voltammetric behavior of receptor 3 has proved to be very sensitive to the presence of Hg 2+ cation. The ability of macrocycle 3 to bind Hg 2+ has also been investigated through electronic structure calculations, being the interaction between the cation and one of the cyclopentadienyl rings the responsible of the different behavior of both redox-active centers.