Ferrocenyl Dendrimers Based on ... - ACS Publications

Article pubs.acs.org/Organometallics

Ferrocenyl Dendrimers Based on Octasilsesquioxane Cores ‡ ́ Marta Herrero,† Beatriz Alonso,*,† José Losada,‡ Pilar Garcıa-Armada, and Carmen M. Casado*,† †

Departamento de Quı ́mica Inorgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco 28049-Madrid, Spain Departamento de Ingenierı ́a Quı ́mica Industrial, Escuela Técnica Superior de Ingenieros Industriales, Universidad Politécnica de Madrid, 28006-Madrid, Spain

‡

S Supporting Information *

ABSTRACT: Hydrosilylation reactions of two octasilsesquioxane dendritic cores containing terminal vinyl groups with bis(ferrocenyl)methylsilane (1) give dendrimers functionalized with 16 (G1-Fc16) and 32 (G2-Fc32) interacting ferrocenyl units. Characterization of the dendrimers by 1H, 13C{1H}, and 29Si{1H} NMR spectroscopy as well as mass spectrometry supports their assigned structures. The thermal behavior of dendrimers G1-Fc16 and G2-Fc32 was studied by TGA techniques. The redox activity of the ferrocenyl centers in G1-Fc16 and G2-Fc32 has been characterized by cyclic voltammetry and square wave voltammetry in dichloromethane containing [n-Bu4N][PF6] as electrolyte support. The solution voltammetric studies of the dendrimers G1-Fc16 and G2-Fc32 exhibit the pattern of communicating ferrocenyl sites with two distinct, separated oxidation waves. The dendrimers were also deposited on electrode surfaces and the electrodes investigated via CV, showing formation of electroactive films with promising results for the use of these materials in the development of biosensors.

D

terminal groups at earlier generations than more conventional cores.13−17 Cuboid octasilsesquioxane has also been derivatized with electroactive ferrocenyl units.18 However, to the best of our knowledge, ferrocenyl dendrimers based on silsesquioxane cores have not been explored yet. The chemistry of ferrocene-containing macromolecular structures has long been one of our aims.7 One of our synthetic approaches to the synthesis of such redox-active organometallic materials was based on hydrosilylation reactions that exploit the reactivity of Si−H polyfunctionalized carbosilane dendrimers,19 cyclotetrasiloxane,20 octasilsesquioxane,18a and siloxane polymers19,21 toward suitable ferrocenyl derivatives containing reactive vinyl or allyl groups. Pursuing our work dealing with the synthesis, functionalization, and study of redox properties and applications22 of new materials containing interacting ferrocene moieties grafted to multifunctional polymers23 and carbosilane dendrimers24 prepared by hydrosilylation of the allyl groups in the polymeric or dendritic backbones with the Si−H functionalized bis(ferrocenyl)silane dendron 1, we report herein the synthesis of two ferrocenyl-terminated dendrimers based on octasilsesquioxane cores, which pose interesting challenges and opportunities.

endrimers are macromolecules with well-defined, highly branched, and nanoscaled architectures. The wide range of potential functions and applications associated with the unique physical and chemical features, due to their special molecular structure, has generated enthusiastic studies in many different disciplines.1−5 From an application point of view, the incorporation of metals into the dendritic framework is of particular interest, as it allows access to highly ordered materials with new magnetic, catalytic, optical, electro- and photochemical, and biomedical properties as well as reactivity. In particular, dendrimers containing redox-active units have been the subject of numerous studies, due to their intriguing electrical and redox properties and their potential use in practical applications such as catalysts, electron transfer mediators, molecular sensors, and electronic devices.6−9 Structurally well-defined polyhedral silsesquioxanes are wellknown molecules with a cubic array of silicon atoms and bridging oxygen atoms that constitute promising candidates for a broad range of technological applications, including those of nanostructured polymers and composites, to which the inorganic core is expected to contribute special properties.10 In particular, octasilsesquioxanes have been used extensively as scaffolds for the development of liquid crystals, biocompatible materials, catalysts, and dendrimers. The chemistry of cubic polyhedral oligosilsesquioxanes has been recently reviewed by Lickiss et al.,11 and polyhedral silsesquioxanes have attracted widespread attention as nanosized building blocks in a wide range of hybrid nanomaterials.12 The use of cubic octasilsesquioxanes as cores for dendrimer synthesis is particularly attractive because not only are minimal synthetic steps required but also their polyhedral structures are expected to produce spherically symmetric dendrimers with a large proportion of © 2012 American Chemical Society

■

RESULTS AND DISCUSSION In this work we have prepared the first-generation dendrimer with octasilsesquioxane as the core and 16 terminal vinyl groups (G1-Vinyl16) by using successive hydrosilylation− alkenylation steps starting with octavinyloctasilsesquioxane Received: June 28, 2012 Published: August 7, 2012 6344

dx.doi.org/10.1021/om300591p | Organometallics 2012, 31, 6344−6350

Organometallics

Article

Scheme 1. Synthesis of Dendrimers G1-Fc16 and G2-Fc32

(G0-Vinyl8) as the core, representing the zeroth generation (Scheme 1).13a These dendritic cores have been used as precursors to attach diferrocenyl units, linked through a silicon atom, at the periphery via hydrosilylation reactions. Synthesis of Polyferrocenyl Dendrimers G1-Fc16 and G2-Fc32. The starting ferrocenylsilane derivative for the present study was bis(ferrocenyl)methylsilane 1, which was synthesized via a salt elimination reaction of ferrocenyllithium and dichloromethylsilane as previously reported.23,24 This organometallic fragment contains a reactive Si−H group which enables its incorporation in Si−vinyl polyfunctionalized octasilsesquioxane cores. While the majority of the hydrosilylation reactions in the field of octasilsesquioxane derivatives occur between Si−H groups of these cubic scaffolds and an unsaturated organic compound, here we report on the inverted concept, where an organometallic compound containing a Si−H function is attached to the surface of octasilsesquioxanes functionalized with unsaturated organic groups. The first- and second-generation dendrimers G1-Fc16 and G2-Fc32, containing 16 and 32 ferrocenyl moieties, were prepared from the reaction of a slight excess of compound 1 with the octasilsesquioxane dendrimers G0-Vinyl8 (which contains one vinyl function in each branch) and G1-Vinyl16

(which contains two vinyl functions in each branch). The reaction of 1 with the dendrimers’ vinyl functions in the presence of catalytic amounts of Karstedt’s catalyst, in toluene solution at 75 °C, afforded the desired hydrosilylated first- and second-generation dendrimers G1-Fc16 and G2-Fc32, respectively, in 48−52% yield (Scheme 1). The 1H NMR olefinic resonances were used to follow the complete hydrosilylation reaction by the disappearance of the double-bond protons in the spectra. After appropriate workup, the crude products were purified by column chromatography on silica using mixtures of hexane and dichloromethane as eluents. Solvent removal afforded the desired dendrimers G1-Fc16 and G2-Fc32, which contain 16 and 32 ferrocenyl moieties, respectively, on the octasilsesquioxane surface, as orange solids. The structures of the novel metallodendritic complexes G1Fc16 and G2-Fc32 were straightforwardly determined on the basis of 1H, 13C{1H}, and 29Si{1H}NMR spectroscopy and matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF-MS). In the 1H NMR spectra of both new compounds, confirming evidence for the complete functionalization of all the reactive Si−vinyl sites in the octasilsesquioxane core with silicon-bridged biferrocenyl moieties is provided by the disappearance of the Si−vinyl 6345


Organometallics

Article

The next weight loss beginning at 520 °C can be assigned to thermal degradation of the octasilsesquioxane cage structure. Finally at 790 °C the TGA curve levels off. The secondgeneration dendrimer G2-Fc32 shows an initial weight loss of approximately 5% near 100 °C, attributable to the removal of toluene followed by a two-step decomposition process. The major weight loss of this generation occurs in the temperature region between 335 and 650 °C, after which the TGA curve is almost leveled off. Interestingly, the dendrimer G2-Fc32 has a higher char yield at 800 °C than the first-generation dendrimer G1-Fc16 at almost the same octasilsesquioxane core content. This is presumably explained by the loss of volatile ferrocenyl fragments during heating, because the ferrocenyl moieties are attached to the octasilsesquioxane core through longer branches, and therefore the elimination of ferrocene is more feasible. Electrochemical Behavior. The electrochemical behavior of the synthesized ferrocenyloctasilsesquioxane dendrimers G1Fc16 and G2-Fc32 has been investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) of the materials in homogeneous solution, as well as in the case of the organometallic dendrimers confined to electrode surfaces (i.e., where the dendrimers serve as electrode modifiers). The cyclic voltammograms of G1-Fc16 and G2-Fc32 in CH2Cl2/[n-Bu4N][PF6] solutions exhibit two well-separated oxidation waves (see, for example, Figure 2A). For both dendrimers, a change in solubility accompanied the change in oxidation state, so that upon scan reversal after the second oxidation process, the reduction wave was dramatically sharpened, giving rise to a cathodic stripping peak. Thus, the complete oxidation of G1-Fc16 and G2-Fc32 in this medium appears to result in the precipitation of the oxidized polyferrocenyl molecules onto the electrode surface, and on the reverse scan the molecules partially redissolve as they are reduced. When acetonitrile is added to the CH2Cl2/[n-Bu4N][PF6] medium, the cathodic stripping peak disappears and the cyclic voltammogram displays the two anodic steps shown in Figure 2B. Both electron transfers exhibit directly associated responses in the reverse scan. For both waves the ratio of cathodic to anodic peak current (ipc/ipa) was close to unity and the plot of peak current vs v1/2 was linear, indicating diffusion-controlled redox processes. The square wave voltammograms of G1-Fc16 and G2-Fc32 in this medium show two separated oxidation waves of the same area (Figure 2C), indicating that an equal number of electrons are transferred in both redox processes. Formal potentials were calculated from the SWV peak potentials, and the results obtained were E°1 = 0.413 and E°2 = 0.568 V (vs SCE) for G1-Fc16 and E°1 = 0.418 and E°2 = 0.558 V (vs SCE) for G2-Fc32. These results suggest that the neutral G1-Fc 16 and G2-Fc 32 undergo two successive oxidations to yield first the octacation (G1-Fc16)8+ or hexadecacation (G2-Fc32)16+ and then the hexadeca (G1Fc16)16+ or dotriaconta (G2-Fc32)32+ cationic species. The presence of two well-separated oxidation waves in the voltammograms of these ferrocenyloctasilsesquioxane dendrimers, also observed in the starting species 1 (see the Supporting Information), is consistent with the existence of interactions between the two iron centers which are linked together by a bridging silicon atom. This two-wave redox response is similar to that found in oligo- and poly(ferrocenylsilanes) reported by Manners and co-workers26 and Pannell et al. 27 polysiloxanes functionalized with

resonances in the region 6.1−5.7 ppm, concomitant with a decrease of the Si−H resonance at δ 4.92 ppm. Interestingly, 1 H and 13C NMR spectra evidence that only the β isomers were formed and no Markonikov addition (which would lead to α isomers) took place, resulting in molecules with maximum symmetry. 1H NMR spectra of G1-Fc16 and G2-Fc32 show in all cases the pattern of resonances in the range 4.1−4.4 ppm characteristic of the unsubstituted and substituted cyclopentadienyl ligands in the ferrocenyl moieties. Methylene groups in the octasilsesquioxane dendritic framework appear as two broad signals in the range 0.9−0.6 ppm, and the resonances of the methyl groups are observed within the range 0.4−0.0 ppm, all with the expected integration ratios. As previously encountered, the two different Si−CH2CH2−Si−CH2CH2−Si disilylethylene segments, belonging to generation 0 and generation 1, respectively, could not be differentiated. The 29 Si{1H} NMR spectra display clearly separated signals for the different types of silicon atoms in the molecules, which can be easily assigned on the basis of the chemical shifts and the peak intensities. Thus, the outermost silicon atoms bridging two ferrocenyl units resonate at −4.6 (for G1-Fc16) and −4.5 (for G2-Fc32), a singlet is observed at −66.4 (for G1-Fc16) and at −66.6 (for G2-Fc32) corresponding to the T-type silicon atoms of the silsesquioxane core,25 and also that of the third different silicon atom in G2-Fc32 appears at 8.2 ppm. The structures of the first- and second-generation dendrimers G1-Fc16 and G2-Fc32 were corroborated by MALDI-TOF mass spectrometry, which showed the molecular ions at m/z 3946.3 and 8043.4, respectively. The thermal behavior of dendrimers G1-Fc16 and G2-Fc32 has been examined by thermogravimetric analysis (TGA). The samples were heated at a ramp rate of 10 °C/min under a nitrogen atmosphere in the temperature range 25−800 °C. The first-generation dendrimer G1-Fc16 starts to lose its weight at a temperature above 150 °C (Figure 1) and shows a

Figure 1. TGA curves for G1-Fc16 and G2-Fc32 recorded under a nitrogen atmosphere.

three-step thermolysis process. At 250 °C approximately only 3% of the initial weight of the sample is lost. The dendrimer undergoes a smooth thermolytic degradation in the temperature region 250−400 °C. By 400 °C only 9% of the initial sample weight is lost, while the major weight loss of this dendrimer occurs in the temperature region of 400−500 °C. 6346


Organometallics

Article

Figure 2. Cyclic voltammograms at a Pt-disk electrode of G1-Fc16 (A) in CH2Cl2 and (B) in CH2Cl2/CH3CN (1/1 by volume) at a scan rate of 100 mV s−1 and (C) square wave voltammogram of G1-Fc16 in CH2Cl2/CH3CN.

Scheme 2. Electrochemical Behavior of Dendrimer G2-Fc32

diferrocenylmethylvinylsilanes,21b and block copolymers23 and related carbosilane dendrimers24 containing diferrocenylmethylsilane units. Thus, the first oxidation of G1-Fc16 and G2Fc32 occurs at nonadjacent ferrocene sites (see for example Scheme 2), which makes the subsequent removal of electrons from the remaining ferrocenyl centers, neighboring those already oxidized, more difficult. It is known that in linked metallocenes the difference in the redox potentials (ΔE°2‑1 = E°2 − E°1) observed for the two waves is taken as a measure of the degree of electronic interaction between the two metal sites.28 From the wave splitting ΔE°2‑1 = 155 mV (for G1-Fc16) and 140 mV (for G2Fc32), and the comproportionation constant Kc relative to the equilibrium among the three oxidation states of the two iron atoms in the dendritic wedges Fe(II)−Fe(II) + Fe(III)−Fe(III) ↔ 2Fe(II)−Fe(III) was calculated,29 resulting in values of Kc = 417 for G1-Fc16 and 233 for G2-Fc32. These values indicate that the partially oxidized dendritic molecules are representative mixed-valence species classified into Robin and Day class II.30 A key feature concerning the ferrocenyloctasilsesquioxane dendrimers G1-Fc16 and G2-Fc32 is their ability to modify electrodes, resulting in electroactive material that remains persistently attached to the electrode surface. The deposition of the dendrimers can be carried out onto Pt or GC electrodes,

and presumably other materials, either by controlled-potential electrolysis at 0.80 V or by repeated cycling between 0.0 and 1.0 V versus SCE in degassed solutions of the dendrimer in CH2Cl2. Thus, the amount of electrodeposited material can be controlled through the time interval during which the potential was held fixed or the number of scans. The surface coverage of electroactive ferrocenyl sites in the film, Γ, was determined from the integrated charge of the cyclic voltammetric waves. The redox behavior of films of the dendrimers electrodeposited onto electrode surfaces was studied by CV in fresh CH2Cl2 solutions containing only the supporting electrolyte. A representative example of the CV responses of an electrodeposited film of G2-Fc32 is shown in Figure 3. In all cases two successive well-defined reversible oxidation−reduction waves due to the existence of appreciable interactions between the two iron centers is observed, with formal potential values of about E°1 = 0.39 V and E°2 = 0.53 V (vs SCE). The shape of the features in the cyclic voltammograms is independent of the scan rate, and repeated scanning in CH2Cl2 electrolyte solutions did not change the voltammograms, demonstrating that films of both dendrimers remain stable to electrochemical cycling. A linear relationship of peak currents with potential sweep rate, v, was observed, and the potential difference between the corresponding cathodic and anodic peaks is 6347


Organometallics

■

Article

EXPERIMENTAL SECTION

Materials and Equipment. All reactions were performed under an inert atmosphere (prepurified N2 or Ar) using standard Schlenk techniques. Solvents were dried by standard procedures over the appropriate drying agents and distilled immediately prior to use. Octavinyloctasilsesquioxane (G0-Vinyl8) (GELEST), Karstedt’s catalyst (platinum divinyltetramethyldisiloxane complex, 2.1−2.4% platinum in vinyl-terminated polydimethylsiloxane) (ABCR), and dichloromethylsilane, vinylmagnesium chloride (1.6 M solution in THF), nbutyllithium (1.6 M in hexane), and tert-butyllithium (1.7 M in pentane) (Aldrich) were used for the preparations. These compounds were used without further purification. Silica gel (70−230 mesh) (Aldrich) was used for column chromatographic purifications. Bis(ferrocenylmethyl)silane 124 and the polyhedral oligomeric silsesquioxane dendrimer core G1-Vinyl1613a were prepared as described in the literature with slight modifications. NMR spectra were recorded on a Bruker AMX-300 spectrometer. Chemical shifts are reported in parts per million (δ) with reference to residual solvent resonances for 1H and 13C NMR (CDCl3; 1H, δ 7.27 ppm; 13C, δ 77.0 ppm). 29Si NMR spectra were recorded with inverse-gated proton decoupling in order to minimize nuclear Overhauser effects. The MALDI-TOF mass spectra were obtained using a Reflex III (Bruker) mass spectrometer equipped with a nitrogen laser emitting at 337 nm. The matrix was trans-2-[3-(4-tert-butylphenyl)-2-methyl-2propenylidene]malononitrile (DCTB) or ditranol. The thermogravimetric analyses were performed using a TGA Q-500 instrument coupled with an EGA oven. Samples (5−10 mg) were loaded in platinum pans. The measurements were carried out under N2 (90 mL min−1) with a heating rate of 10 °C min−1 from 25 to 800 °C. Electrochemical Measurements. Electrochemical measurements were performed using an Autolab PGSTAT 128N. CH3CN and CH2Cl2 (spectrograde) for electrochemical measurements were freshly distilled from calcium hydride under nitrogen. The supporting electrolyte used was tetra-n-butylammonium hexafluorophosphate ([n-Bu4N][PF6]), which was purchased from Fluka. The supporting electrolyte concentration was typically 0.1 M. A conventional sample cell operating under an atmosphere of prepurified nitrogen was used for cyclic voltammetry. All cyclic voltammetric experiments were performed using either a platinum-disk working electrode (A = 0.020 cm2) or a glassy-carbon-disk working electrode (A = 0.070 cm2), each of which was polished prior to use with either 0.05 μm alumina/water slurry or 1 μm diamond paste (Buehler) and rinsed thoroughly with purified water and acetone. All potentials are referenced to the saturated calomel electrode (SCE). A coiled platinum wire was used as a counter electrode. Solutions for cyclic voltammetry were typically 0.5 mM in the redox-active species and were deoxygenated by purging with prepurified nitrogen. No iR compensation was used. SWV was done with a step potential of 1 mV, a square wave frequency of 25 Hz, and a square wave amplitude of 10 mV. Synthesis of Dendrimer G1-Fc16. To a toluene solution (10 mL) of G0-Vinyl8 (0.10 g, 0.16 mmol) was added 50 μL of Karstedt’s catalyst. The mixture was stirred at room temperature for approximately 0.5 h. A solution of bis(ferrocenylmethyl)silane 1 (0.60 g, 1.45 mmol) in dry toluene (20 mL) was added dropwise, and the mixture was warmed to 75 °C. The attachment of bis(ferrocenylmethyl)silane dendron 1 to the eight Si−vinyl active sites of the dendritic core proceeded cleanly to completion in 24 h, as was established from 1H NMR analysis of the reaction mixture, which showed the disappearance of signals due to the Si−vinyl function. The mixture was cooled to room temperature, and the solvent was removed under vacuum. The orange oil residue was treated with hexane and subjected to column chromatography on silica gel. From elution with hexane/dichloromethane 5/1 a first band containing 1 was separated. The orange band eluted with hexane/dichloromethane 1/1 afforded G1-Fc16 as an orange air-stable solid. Yield: 0.32 g (52%). 1 H NMR (CDCl3, 300 MHz): δ 4.29 (m, 32H, C5H4), 4.06 (m, 32H, C5H4), 4.05 (s, 80H, C5H5), 0.92 (m, 16H, CH2), 0.73 (m, 16H, CH2), 0.36 (s, 24H, SiCH3). 13C{1H} NMR (CDCl3, 75.43 MHz): δ 73.73, 70.81, 70.64, 70.16 (C5H4), 68.48 (C5H5), 8.24 (CH2), 5.22 (CH2), -

Figure 3. Voltammetric response of a Pt-disk electrode modified with a film of dendrimer G2-Fc32, measured in CH2Cl2/[n-Bu4N][PF6] at different scan rates. Γ = 6.8 × 10−11 mol Fc/cm2.

smaller than 10 mV at scan rates of 0.1 V s−1 or less (see the Supporting Information). These voltammetric features unequivocally indicate the surface-confined nature of the electroactive dendrimer film.31 Likewise, after standing in air for several weeks, the redox response was practically unchanged with no loss of electroactivity. The high stability of these surface-confined poly(ferrocenyl) dendrimer films is an important observation, since the applications of modified electrodes require extensive redox cycling. Electrodes modified with polymers and dendrimers containing electronically communicating ferrocenyl moieties have been shown to be useful in the development of biosensors.7a In our search for new, more robust, and improved biosensors, and taking into account that the sensor behavior is affected by the structural characteristics of the mediator, the development of new biosensors in which the mediators are flexible dendrimers grown from a polyhedral core which will provide a large proportion of interacting ferrocenyl terminal groups is one of our goals. We assume that the behavior of modified electrodes of G1-Fc16 and G2-Fc32 is related to very thin dendrimer layers without diffusion problems, which is also of great importance especially for catalytic reactions in biosensors. Work in this direction in now underway and will be reported in future publications.

■

CONCLUSIONS First and second generations of octasilsesquioxane dendrimers, peripherally functionalized with 16 and 32 ferrocenyl units, have been prepared by hydrosilylation of the vinyl groups in the dendrimers G0-Vinyl8 and G1-Vinyl16 with bis(ferrocenyl)methylsilane 1 containing a Si−H function and adequately characterized. Solution voltammetric studies of dendrimers G1Fc16 and G2-Fc32 show two well-separated reversible redox processes, indicating electronic communication between the metal sites in the periphery of the dendritic structures. In addition, we have demonstrated the feasibility of modifying electrode surfaces with stable electroactive films of these poly(ferrocenyl)octasilsesquioxane dendrimers. The results of the electrochemical studies bear promise for the use of these dendrimers in biosensors. 6348


Organometallics

Article

3.10 (SiCH3). 29Si{1H} NMR (CDCl3, 59.3 MHz): δ −4.6 (SiCH3), −66.4 (SiO). MS (MALDI-TOF): m/z 3946.3 [M+]. Synthesis of Dendrimer G2-Fc32. Using the same method as detailed for the preparation of G1-Fc16, dendrimer G2-Fc32 was synthesized by starting from 1 (0.56 g, 1.36 mmol) and G1-Vinyl16 (0.10 g, 0.07 mmol). After purification by column chromatography using hexane/dichloromethane (1/2) as eluent, the desired ferrocenyl dendrimer G2-Fc32 was isolated as an air-stable orange solid. Yield: 0.27 g (48%). 1H NMR (CDCl3, 300 MHz): δ 4.35 (m, 64H, C5H4), 4.12 (m, 64H, C5H4), 4.09 (s, 160H, C5H5), 0.83 (m, 48H, CH2), 0.60 (m, 48H, CH2), 0.50 (s, 48H, SiCH3Fc), −0.007 (s, 24H, SiCH3). 13 C{1H} NMR (CDCl3, 75.43 MHz): δ 73.57, 73.49, 70.73, 70.67, 70.50 (C5H4), 68.36 (C5H5), 8.68 (CH2), 5.13, 4.81 (CH2), −2.96 (SiCH3Fc), −6.02 (SiCH3). 29Si{1H} NMR (CDCl3, 59.3 MHz): δ 8.2 (SiCH2), −4.5 (SiCH3Fc), −66.6 (SiO). MS (MALDI-TOF): m/z 8043.4 [M+].

■

(10) (a) Applications of Polyhedral Oligomeric Silsesquioxanes; Hartmann-Thompson, C., Ed.; Springer: New York, 2011. (b) Lickiss, P. D.; Rataboul, F. In Advances in Organometallics Chemistry; Hill, A. F., Fink, M. J., Eds.; Academic Press: Oxford, U.K., 2008; Vol. 57, pp 1− 116. (11) For an extensive review, see: Cordes, D. B.; Lickiss, P. D.; Rataboul, F. Chem. Rev. 2010, 110, 2081. (12) Pielichowski, K.; Njuguna, J.; Janowski, B.; Pielichowski, J. Adv. Polym. Sci. 2006, 201, 225. (13) (a) Jaffrès, P.-A.; Morris, R. E. J. Chem. Soc., Dalton Trans. 1998, 2767. (b) Coupar, P. I.; Jaffrès, P.-A.; Morris, R. E. J. Chem. Soc., Dalton Trans. 1999, 2183. (c) Ropartz, L.; Morris, R. E.; Foster, D. F.; Cole-Hamilton, D. J. Chem. Commun. 2001, 361. (d) Ropartz, L.; Foster, D. F.; Morris, R. E.; Slawin, A. M. Z.; Cole-Hamilton, D. J. Dalton Trans. 2002, 1997. (14) (a) Feher, F. J.; Wyndham, K. D. Chem. Commun. 1998, 323. (b) Feher, F. J.; Wyndham, K. D.; Soulivong, D.; Nguyen, F. J. Chem. Soc., Dalton Trans. 1999, 1491. (15) (a) Hong, B.; Thoms, T. P. S.; Murfee, H. J.; Lebrun, M. J. Inorg. Chem. 1997, 36, 6146. (b) Murfee, H. J.; Thoms, T. P. S.; Greaves, J.; Hong, B. Inorg. Chem. 2000, 39, 5209. (16) (a) Naka, K.; Fujita, M.; Tanaka, K.; Chujo, Y. Langmuir 2007, 23, 9057. (b) Tanaka, K.; Inafuku, K.; Naka, K.; Chujo, Y. Org. Biomol. Chem. 2008, 6, 3899. (17) Wada, K.; Watanabe, N.; Yamada, K.; Kondo, T.; Mitsudo, T. Chem. Commun. 2005, 95. (18) (a) Morán, M.; Casado, C. M.; Cuadrado, I.; Losada, J. Organometallics 1993, 12, 4327. (b) Casado, C. M.; Cuadrado, I.; Morán, M.; Alonso, B.; Barranco, M.; Losada, J. Appl. Organomet. Chem. 1999, 13, 245. (c) Losada, J.; Garcı ́a Armada, M. P.; Cuadrado, I.; Alonso, B.; González, B.; Casado, C. M.; Zhang, J. J. Organomet. Chem. 2004, 689, 2799. (d) Bruña, S.; Nieto, D.; González-Vadillo, A. M.; Perles, J.; Cuadrado, I. Organometallics 2012, 31, 3248. (19) (a) Alonso, B.; Cuadrado, I.; Morán, M.; Losada, J. J. Chem. Soc., Chem. Commun. 1994, 2575. (b) Alonso, B.; Morán, M.; Casado, C. M.; Lobete, F.; Losada, J.; Cuadrado, I. Chem. Mater. 1995, 7, 1440. (c) Cuadrado, I.; Casado, C. M.; Alonso, B.; Morán, M.; Losada, J.; Belsky, V. J. Am. Chem. Soc. 1997, 119, 7613. (d) Garcı ́a, B.; Casado, C. M.; Cuadrado, I.; Alonso, B.; Morán, M.; Losada, J. Organometallics 1999, 18, 2349. (e) Ramı ́rez, E.; Cuadrado, I.; Casado, C. M.; Losada, J.; Alonso, B. J. Organomet. Chem. 2006, 691, 1131. (f) Zamora, M.; Alonso, B.; Pastor, C.; Cuadrado, I. Organometallics 2007, 26, 5153. (20) Casado, C. M.; Cuadrado, I.; Morán, M.; Alonso, B.; Lobete, F.; Losada, J. Organometallics 1995, 14, 2618. (21) (a) Casado, C. M.; Morán, M.; Losada, J.; Cuadrado, I. Inorg. Chem. 1995, 34, 1668. (b) Alonso, B.; González, B.; Ramı ́rez, E.; Zamora, M.; Casado, C. M.; Cuadrado, I. J. Organomet. Chem. 2001, 637−639, 642. (22) (a) Losada, J.; Cuadrado, I.; Morán, M.; Casado, C. M.; Alonso, B.; Barranco, M. Anal. Chim. Acta 1997, 338, 191. (b) Garcı ́a Armada, M. P.; Losada, J.; Cuadrado, I.; Alonso, B.; González, B.; Ramı ́rezOliva, E.; Casado, C. M. Sensor. Actuat. B: Chem. 2003, 88, 190. (c) Garcı ́a Armada, M. P.; Losada, J.; Cuadrado, I.; Alonso, B.; González, B.; Casado, C. M. Electroanalysis 2003, 15, 1109. (d) Garcı ́a Armada, M. P.; Losada, J.; Cuadrado, I.; Alonso, B.; González, B.; Casado, C. M.; Zhang, J. Sensor. Actuat. B: Chem. 2004, 101, 143. (e) Losada, J.; Garcı ́a Armada, M. P.; Cuadrado, I.; Alonso, B.; González, B.; Zhang, J.; Casado, C. M. J. Organomet. Chem. 2004, 689, 2799. (f) Garcı ́a Martínez, M.; Alonso, B.; Casado, C. M.; Losada, J.; Garcı ́a-Armada, P. Electroanalysis 2011, 23, 2888. (23) (a) López-Villanueva, F. J.; Garcı ́a Marcos, A.; Fischer, K.; Schmidt, M.; Alonso, B.; Casado, C. M. M.; Garcı ́a Armada, P.; Losada, J.; Frey, H. Polym. Prepr., Am. Chem. Soc 2006, 47, 1087. (b) Garcı ́a Armada, M. P.; Losada, J.; López-Villanueva, F. J.; Frey, H.; Alonso, B.; Casado, C. M. J. Organomet. Chem. 2008, 693, 2803. (24) Losada, J.; Garcı ́a-Armada, P.; Robles, V.; Martı ́nez, Á . M.; Casado, C. M.; Alonso, B. New J. Chem. 2011, 35, 2187. (25) Smith, A. L., Ed. The Analytical Chemistry of Silicones; Wiley: New York, 1991.

ASSOCIATED CONTENT

S Supporting Information *

Figures giving NMR and mass spectra for G1-Fc16 and G2-Fc32 and additional CVs and SWVs for G1-Fc16, G2-Fc32, and 1. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (B.A.); carmenm.casado@ uam.es (C.M.C.). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work has been supported by the Spanish Ministerio de Ciencia e Innovación (CTQ2009-12332-C02). M.H. acknowledges the Ministerio de Ciencia e Innovación for a predoctoral fellowship.

■

REFERENCES

(1) (a) Campagna, S., Ceroni, P., Puntoriero, F., Eds. Designing Dendrimers; Wiley-VCH: Weinheim, Germany, 2012. (b) Vögtle, F.; Richart, G.; Werner, N. Dendrimer Chemistry. Concepts, Syntheses, Properties, Applications; Wiley-VCH: Weinheim, Germany, 2009. (c) Frechet, J. M. J., Tomalia, D. A., Eds. Dendrimers and Other Dendritic Polymers; VCH: Weinheim, Germany, 2002. (d) Newkome, G. R.; Moorefield, C. N.; Vögtle, F. Dendrimers and Dendrons. Concept, Synthesis and Applications; Wiley-VCH: Weinheim, Germany, 2001. (2) (a) Astruc, D.; Boisselier, E.; Ornelas, C. Chem. Rev. 2010, 110, 1857. (b) Newkome, G. R.; Shreiner, C. Chem. Rev. 2010, 110, 6338. (3) Méry, D.; Astruc, D. Coord. Chem. Rev. 2006, 250, 1965. (4) Tomalia, D. A.; Frechet, J. M. Prog. Polym. Sci. 2005, 30, 217. (5) Advances in Dendritic Macromolecules; Newkome, G. R., Ed.; JAI Press: Greenwich, CT, 1994,1995, 1996, 1999, 2002; Vols. 1−5. (6) (a) Astruc, D. Nature Chem. 2012, 4, 255. (b) Astruc, D. New J. Chem. 2011, 35, 764. (c) Astruc, D.; Daniel, M.-C.; Nlate, S.; Ruiz, J. In Trends in Molecular Electrochemistry; Pombeiro, A. J. L., Amatore, C., Eds.; Marcel Dekker/FontisMedia: New York/Lausanne, 2004; Chapter 9, pp 283−310. (7) (a) Casado, C. M.; Alonso, B.; Losada, J.; Garcı ́a-Armada, M. P. In Designing Dendrimers; Campagna, S., Ceroni, P., Puntoriero, F., Eds.; Wiley-VCH: Weinheim, Germany, 2012; p 219. (b) Casado, C. M.; Cuadrado, I.; Morán, M.; Alonso, B.; Garcı ́a, B.; González, B.; Losada, J. Coord. Chem. Rev. 1999, 185−186, 53. (8) Zanello, P. Inorganic Electrochemistry: Theory, Practice and Application; Royal Society of Chemistry: Cambridge, U.K., 2003. (9) Kaifer, A. E.; Gomez-Kaifer, M. Supramolecular Electrochemistry; Wiley-VCH: Weinheim, Germany, 1999. 6349


Organometallics

Article

(26) (a) Rulkens, R.; Lough, A. L.; Manners, I.; Lovelace, S. R.; Grant, C.; Geiger, W. E. J. Am. Chem. Soc. 1996, 118, 12683. (b) Nguyen, P.; Lopez-Elipe, P.; Manners, I. Chem. Rev. 1999, 99, 1515. (27) (a) Pannel, K.; Dementiev, V.; Li, H.; Cervantes-Lee, F.; Nguyen, M. T.; Diaz, A. F. Organometallics 1994, 13, 3644. (b) Sharma, H. K.; Pannell, K. H.; Ledoux, I.; Zyss, J.; Ceccanti, A.; Zanello, P. Organometallics 2000, 19, 770. (28) For excellent reviews on metal−metal interactions in bridged metallocene systems see: (a) Astruc, D. Acc. Chem. Res. 1997, 30, 383. (b) Barlow, S.; O’Hare, D. Chem. Rev. 1997, 97, 637. (29) Richardson, D. E.; Taube, H. Inorg. Chem. 1981, 20, 1278. (30) Robin, M. B.; Day, P. Adv. Inorg. Chem. Radiochem. 1967, 10, 247. (31) Murray, R. W. In Molecular Design of Electrode Surfaces; Murray, R. W., Ed.; Wiley: New York, 1992; Techniques of Chemistry XXII.

6350


Ferrocenyl Dendrimers Based on ... - ACS Publications

Recommend Documents