Vinyl-Functionalized Silanes and Disiloxanes with Electronically

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Organometallics 2010, 29, 2796–2807 DOI: 10.1021/om1002733

Vinyl-Functionalized Silanes and Disiloxanes with Electronically Communicated Ferrocenyl Units† Sonia Bru~ na,‡ Ana Ma Gonzalez-Vadillo,‡ Daniel Nieto,‡ Cesar Pastor,§ and Isabel Cuadrado*,‡ ‡

Departamento de Quı´mica Inorg anica, §Laboratorio de Difracci on de Rayos X del Servicio Interdepartamental de Investigaci on, Facultad de Ciencias, Universidad Aut onoma de Madrid, Cantoblanco, 29049, Madrid, Spain Received April 6, 2010

A new series of vinyl-functionalized polyferrocenyl organosilicon compounds, including triferrocenylvinylsilane, (CH2dCH)Si(Fc)3 (7) (Fc = (η5-C5H4)Fe(η5-C5H5)), 1,3-divinyl-1,1,3,3-tetraferrocenyldisiloxane, [(CH2dCH)(Fc)2Si]2O (8), and 1,3-divinyl-1,3-dimethyl-1,3-diferrocenyldisiloxane, [(CH2dCH)(Fc)MeSi]2O (9), have been synthesized via the low-temperature salt metathesis reaction of monolithioferrocene and the chlorosilanes (CH2dCH)SiCl3 and [(CH2dCH)(Cl)MeSi]2O. Compounds 7-9 were characterized by elemental analysis, multinuclear (1H, 13C, 29Si) NMR spectroscopy, and MALDI-TOF mass spectrometry. The molecular structures of the vinyl-functionalized silane 7 and divinyldisiloxanes 8 and 9 in the solid state have been determined by single-crystal X-ray analysis. Whereas tetraferrocenyl compound 8 possesses a linear disiloxane skeleton (Si-O-Si bond angle of 180.0(2)°), biferrocenyl 9 shows a bent arrangement of the disiloxane linkage (Si-O-Si angle of 143.2(2)°). The oxidation electrochemical behavior of polyferrocenyl molecules 7-9 has been examined by cyclic voltammetry and square wave voltammetry in dichloromethane solution, using hexafluorophosfate, [PF6]-, and tetrakis(pentafluorophenyl)borate, [B(C6F5)4]-, as supporting electrolyte anions of different coordinating ability. Compound 7 can be reversibly oxidized in three consecutive steps to the trication 73þ. Divinyldisiloxanes 8 and 9 are reversibly oxidized in four and two one-electron-transfer steps, respectively, which suggests significant electronic interaction among the ferrocenyl redox centers linked by the short three-atom Si-O-Si bridge.

Introduction Construction of multimetallic systems containing multiple metallocene moieties continues to attract considerable scientific interest in various areas of research due to possible electronic communication and mixed-valence behavior.1-6 This type of organometallic structure is of great interest for the study of electron-transfer processes and for their potential applications in the modification of electrode surfaces, construction of electronic devices, and electron storage. In particular, compounds containing multiple ferrocenyl units †

Dedicated to Professor Vicente Fernandez Herrero on the occasion of his 65th birthday. *Corresponding author. E-mail: [email protected]. Phone: (þ34) 91 497 4834. Fax: (þ34) 91 497 4833. (1) Zanello, P. In Inorganic Electrochemistry. Theory, Practice and Application; Zanello, P., Ed.; Royal Society of Chemistry: Cambridge, 2003; Chapter 4. (2) Barlow, S.; O’Hare, D. Chem. Rev. 1997, 97, 637. (3) Manners, I. In Synthetic Metal-Containing Polymers; Manners, I., Ed.; Wiley-VCH: Weinheim, Germany, 2004; p 237. (4) Nguyen, P.; G omez-Elipe, P.; Manners, I. Chem. Rev. 1999, 99, 1515. (5) (a) Astruc, D. Electron-Transfer and Radical Processes in Transition Metal Chemistry; VCH: New York, 1995; Chapter 1. (b) Astruc, D. Acc. Chem. Res. 1997, 30, 383. (6) Supramolecular Electrochemistry; Kaifer, A. E., Gomez-Kaifer, M., Eds.; Wiley-VCH: Weinheim: Germany, 1999; Chapter 16. pubs.acs.org/Organometallics

Published on Web 06/02/2010

linked together by a variety of bridging spacer units represent interesting examples of such compounds, because the wellbehaved redox chemistry of the 18-electron ferrocene system7 provides a powerful electrochemical probe to investigate electronic interaction between metal centers through space or through bonds. Some noteworthy examples of welldefined oligoferrocene structures displaying significant electronic communication, in which multiple ferrocenyl moieties are connected by bridging spacers with main-group elements,8,9 include the linear and cyclic oligo(ferrocenylsilanes) (7) Geiger, W. E. Organometallic Electrochemistry: Origins, Development and Future. Organometallics 2007, 26, 5738. (8) For excellent recent reviews on the chemistry of polymetallocenes in which the organometallic units are connected by bridging spacers containing main-group elements see, for example: (a) Herbert, D. E.; Mayer, U. F. J.; Manners, I. Angew. Chem., Int. Ed. 2007, 46, 5060. (b) Bellas, V.; Rehahn, M. Angew. Chem., Int. Ed. 2007, 46, 5082. (9) For recent examples of oligomeric ferrocenyl compounds having electronically communicated ferrocenyl units assembled through carbon-based spacers see, for instance: (a) Yu, Y.; Bond, A. D.; Leonard, P. W.; Lorenz, U. J.; Timofeeva, T. V.; Vollhardt, K. P. C.; Whitener, G. D.; Yakovenko, A. A. Chem. Commun. 2006, 2572. (b) Skibar, W.; Kopacka, H.; Wurst, K.; Salzmann, C.; Ongania, K.-H.; Fabrizi de Biani, F.; Zanello, P.; Bildstein, B. Organometallics 2004, 23, 1024. (c) Santi, S.; Orian, L.; Dono~ni, A.; Bisello, A.; Scapinello, M.; Benetollo, F.; Ganis, P.; Ceccon, A. Angew. Chem., Int. Ed. 2008, 47, 5331. (d) Lohan, M.; Ecorchard, P.; R€uffer, T.; Justaud, F.; Lapinte, C.; Lang, H. Organometallics 2009, 28, 1878. r 2010 American Chemical Society

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Chart 1

of Manners and co-workers,10,11 Pannell et al.,12 and K€ oller et al.,13 the polyferrocenylphosphines of Kirss and Geiger et al.,14 the boron-bridged polyferrocenylenes by Wagner and co-workers,15 the sulfur-bridged ferrocenes of Rauchfuss et al.16 and of Long and Zanello et al.,17 and the small polyferrocenyl dendritic molecules reported by Kaifer et al.18 and by our own group.19 On the other hand, ferrocene derivatives possessing reactive functionalities tethered to the cyclopentadienyl rings have been extensively used to synthesize a broad variety of ferrocenyl-containing molecules with interesting applications, ranging from homogeneous catalysis to molecular recognition and materials science.20 Our group has a long-standing (10) (a) Herbert, D. E.; Gilroy, J. B.; Chan, W. Y.; Chabanne, L.; Staubitz, A.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2009, 131, 14958. (b) Chan, W. Y.; Lough, A. J.; Manners, I. Angew. Chem., Int. Ed. 2007, 46, 9069. (c) MacLachlan, M. J.; Lough, A. J.; Geiger, W. E.; Manners, I. Organometallics 1998, 17, 1873. (11) (a) Rulkens, R.; Lough, A. J.; Manners, I.; Lovelace, S. R.; Grant, C.; Geiger, W. E. J. Am. Chem. Soc. 1996, 118, 12683. (b) Rulkens, R.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 1994, 116, 797. (c) Foucher, D.; Honeyman, C. H.; Nelson, J. M.; Zhong Tang, B.; Manners, I. Angew. Chem., Int. Ed. Engl. 1993, 32, 1709. (12) (a) Pannell, K. H.; Dementiev, V. V.; Li, H.; Cervantes-Lee, F.; Nguyen, M. T.; Diaz, A. F. Organometallics 1994, 13, 3644. (b) Dementiev, V. V.; Cervantes-Lee, F.; Parkanyi, L.; Sharma, H.; Pannell, K. H.; Nguyen, M. T.; Diaz, A. F. Organometallics 1993, 12, 1983. (c) Nguyen, M. T.; Diaz, A. F.; Dementiev, V. V.; Pannel, K. H. Chem. Mater. 1993, 5, 1389. (13) Grossmann, B.; Heinze, J.; Herdtweck, E.; K€ ohler, F. H.; Noth, H.; Schwenk, H.; Spiegler, M.; Wachter, W.; Weber, B. Angew. Chem., Int. Ed. 1997, 36, 387. (14) Barriere, G. F.; Kirss, R. U.; Geiger, W. E. Organometallics 2005, 24, 48. (15) Kaufmann, L.; Breunig, J.-M.; Vitze, H.; Schoedel, F.; Nowik, I.; Pichlmaier, M.; Bolte, M.; Lerner, H.-W.; Winter, R. F.; Herber, R. H.; Wagner, M. Dalton Trans. 2009, 2940. (16) Brandt, P. F.; Rauchfuss, T. B. J. Am. Chem. Soc. 1992, 114, 1926. (17) Gibson, V. C.; Long, N. J.; Long, R. J.; White, A. J. P.; Williams, C. K.; Williams, D. J.; Grigiotti, E.; Zanello, P. Organometallics 2004, 23, 957. (18) Alvarez, J.; Ren, T.; Kaifer, A. E. Organometallics 2001, 20, 3543. (19) Cuadrado, I.; Casado, C. M.; Alonso, B.; Moran, M.; Losada, J.; Belsky, V. J. Am. Chem. Soc. 1997, 119, 7613. (20) (a) Ferrocenes. Ligands Materials and Biomolecules; Stepnicka, P., Ed.; John Wiley & Sons: West Sussex, 2008. (b) Ferrocenes: Homogeneous Catalysis-Organic Synthesis-Materials Science; Togni, A., Hayashi, T., Eds.; VCH: Weinheim, Germany, 1995.

Scheme 1. Synthesis of Vinyl-Functionalized Polyferrocenyl Compounds 7-9

interest in functionalized ferrocenes as well as in ferrocenecontaining dendrimers and polymers.21-23 Within this context, we have been exploring the chemistry of alkenyl-functionalized silicon-based organometallic compounds, and we (21) Cuadrado, I. In Silicon-Containing Dendritic Polymers; Dvornic, P., Owen, M. J., Eds.; Springer, 2009; p 141. (22) (a) Cuadrado, I.; Moran, M.; Casado, C. M.; Alonso, B.; Losada, J. Coord. Chem. Rev. 1999, 193-195, 395. (b) Casado, C. M.; Gonzalez, B.; Cuadrado, I.; Alonso, B.; Moran, M.; Losada, J. Angew. Chem., Int. Ed. 2000, 39, 2135. (c) Cuadrado, I.; Moran, M.; Casado, C. M.; Alonso, B.; Lobete, F.; García, B.; Ibisate, M.; Losada, J. Organometallics 1996, 15, 5278. (d) Gonzalez, B.; Casado, C. M.; Alonso, B.; Cuadrado, I.; Moran, M.; Wang, Y.; Kaifer, A. E. Chem. Commun. 1998, 2569. (e) Alonso, B.; Cuadrado, I.; Moran, M.; Losada, J. J. Chem. Soc., Chem. Commun. 1994, 2575. (f) Alonso, B.; Moran, M.; Casado, C. M.; Lobete, F.; Losada, J.; Cuadrado, I. Chem. Mater. 1995, 7, 1440. (g) Castro, R.; Cuadrado, I.; Alonso, B.; Casado, C. M.; Moran, M.; Kaifer, A. J. Am. Chem. Soc. 1997, 119, 5760. (h) Zamora, M.; Herrero, S.; Losada, J.; Cuadrado, I.; Casado, C. M.; Alonso, B. Organometallics 2007, 26, 2688. (23) (a) Casado, C. M.; Cuadrado, I.; Moran, M.; Alonso, B.; Lobete, F.; Losada, J. Organometallics 1995, 14, 2618. (b) Casado, C. M.; Moran, M.; Losada, J.; Cuadrado, I. Inorg. Chem. 1995, 34, 1668. (c) Moran, M.; Casado, C. M.; Cuadrado, I.; Losada, J. Organometallics 1993, 12, 4327.

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Scheme 2. Possible Synthetic Pathway for the Formation of Tetrametallic Compound 8

have described synthetic methods for obtaining a variety of molecules containing Si-CHdCH2 or Si-CH2-CHdCH2 functionalies.19,21,24 Examples of such derivatives include compounds 1-6, shown in Chart 1. Indeed, vinyl- and allylfunctionalized organosilicon derivatives constitute a versatile class of functional molecules of potentially wide applicability in modern organosilicon chemistry.25 Specifically, we have used compounds 1-6 for the construction of homoand heterometallic dendritic and polymeric structures, via hydrosylilation reactions.19,21,24 Likewise, Pannell and coworkers have recently established that compounds 1 and 5 act as efficient monomers for the synthesis of remarkable ferrocenylene copolymers and sila[1]ferrocenophanecontaining compounds.26 In addition, the interesting chemical behavior of 1,10 -bis(dimethylvinylsilyl)ferrocene (1) and 1,10 -bis(diphenylvinylsilyl)ferrocene in ruthenium-catalyzed silylative coupling cyclization reactions has been investigated by Marciniec and co-workers.27 On the other hand, Manners and co-workers have recently reported interesting examples of polyferrocenylsilanes containing Si-vinyl and Si-allyl side chains, which were prepared by ring-opening polymerization of strained methylvinylsila[1]ferrocenophane and methylallylsila[1]ferrocenophane.28 As a continuation of our studies on the chemistry of vinyl-functionalized silicon-containing organometallic compounds, this contribution describes our recent results regarding the preparation of structurally new types of ferrocenyl-containing vinylsilanes and divinyldisiloxanes molecules, which represent useful (24) Zamora, M.; Alonso, B.; Pastor, C.; Cuadrado, I. Organometallics 2007, 26, 5153. (b) Alonso, B.; Gonzalez, B.; Ramírez, E.; Zamora, M.; Casado, C. M.; Cuadrado, I. J. Organomet. Chem. 2001, 637-639, 642. (c) García, B.; Casado, C. M.; Cuadrado, I.; Alonso, B.; Moran, M.; Losada, J. Organometallics 1999, 18, 2349. (d) Ramírez-Oliva, E.; Cuadrado, I.; Alonso, B. J. Organomet. Chem. 2006, 691, 1131. (25) (a) Hydrosilylation. A Comprehensive Review on Recent Advances. Advances in Silicon Science, Vol. 1; Marciniec, B., Ed.; Springer Science, 2009. (b) Luh, T. Y.; Liu, S. T. In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, 1998. (c) Comprehensive Handbook on Hydrosilylation; Marciniec, B., Ed.; Pergamon Press: Oxford, 1992. (d) Ojima, I. In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; John Wiley & Sons: New York, 1989; Part 2, p 1479. (26) (a) Kumar, M.; Metta-Magana, A. J.; Pannell, K. H. Organometallics 2008, 27, 6457. (b) Kumar, M.; Pannell, K. H. J. Inorg. Organomet. Polym. 2008, 18, 131. (27) Majchrzak, M.; Marciniec, B.; Kubicki, M.; Paweczyk, A. Organometallics 2005, 24, 3731. (28) (a) Hilf, S.; Cyr, H.; Rider, D.; Manners, I.; Ishida, T.; Chujo, Y. Macromol. Rapid Commun. 2005, 26, 950. (b) McDowell, J. F.; Zacharia, N. S.; Puzzo, D.; Manners, I.; Ozin, G. A. J. Am. Chem. Soc. 2010, 132, 3236.

precursor reagents for further synthesis and chemical transformations. We report herein the synthesis and full details of the spectroscopic, structural, and redox characterization of novel Si-vinyl-functionalized multimetallic molecules containing three (7), four (8), and two (9) ferrocenyl units linked by siloxanes or silicon bridges. Their electrochemical behavior has been studied, especially with regard to the electronic interactions between the ferrocenyl moieties linked through the three-atom Si-O-Si bridge.

Results and Discussion Synthesis and Characterization of Ferrocenyl-Functionalized VinylSilane 7 and Divinyl-Disiloxanes 8 and 9. Triferrocenylvinylsilane (7) was synthesized via salt elimination reaction of ferrocenyllithium (η5-C5H4Li)Fe(η5-C5H5) and trichlorovinylsilane in THF at low temperature (Scheme 1). Our initial attempts to prepare 7 with three ferrocenyl substituents attached to the silicon atom involved the use of (tri-n-butylstannyl)ferrocene in order to generate pure monolithioferrocene. After appropriate workup of the crude reaction mixture, column chromatography on silica gave a first orange band containing unreacted ferrocene followed by several other orange products, the first of which contained the desired vinyl-terminated triferrocenyl product 7, which was isolated in high purity as an orange crystalline solid. Surprisingly, during the column chromatographic purification of the trimetallic 7, a new yellow-orange crystalline compound was also isolated in low yield (see Experimental Section) and was unequivocally identified as the disiloxane 8 on the basis of multinuclear (1H, 13C, 29Si) NMR spectroscopy, mass spectrometry, and X-ray studies. Most likely, this initially unexpected tetrametallic compound 8 was formed under the used reaction conditions, as a result of the condensation reaction of silanol-containing diferrocenyl molecules,29 in turn generated accidentally, either by partial hydrolysis of the starting trichlorovinylsilane or by hydrolysis of chlorodiferrocenylvinylsilane molecules, as suggested in Scheme 2. (29) Formation of siloxane-bridged di- and polynuclear ferrocenes starting from silanediol-containing ferrocenyl species has been reported by Pannell et al. and by the Manners group: (a) MacLachlan, M. J.; Zheng, J.; Lough, A. J.; Manners, I.; Mordas, C.; LeSuer, R. J.; Geiger, W. E.; Liable-Sands, L. M.; Rheingold, A. L. Organometallics 1999, 18, 1337. (b) Reyes-García, E. A.; Cervantes-Lee, F.; Pannell, K. H. Organometallics 2001, 20, 4734. See also: Zhang, Y.; Cervantes-Lee, F.; Pannell, K. H. Organometallics 2003, 22, 510.

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Figure 1. 500 MHz 1H NMR spectrum, in (CD3)2CO, of bimetallic compound 9 (inset: expanded view of vinyl, cyclopentadienyl, and methyl regions).

Preliminary electrochemical measurements of the tetrametallic disiloxane 8 revealed an interesting multistep electron-transfer system that suggested significant electronic interaction among the four ferrocenyl centers (vide infra). This result encouraged us to search for a structurally simpler divinyl derivative, such as the bimetallic model compound 9, containing only two ferrocenyl moieties linked through the three-atom short Si-O-Si bridge. The synthesis of 9 was conveniently accomplished by reaction of lithioferrocene with 1,3-divinyl-1,3-dimethyl-1,3-dichlorodisiloxane in THF at low temperature. In this synthesis, monolithioferrocene was directly generated in situ from the reaction between ferrocene and t-BuLi in THF at low temperature. After appropriate workup, the divinyl-terminated 9 was isolated in high purity and reasonable yield, as an orange crystalline solid. Compounds 7-9 were found to be soluble in common organic solvents and can be stored for a long period (several months) under an air atmosphere at room temperature without noticeable decomposition (1H NMR spectroscopy). The structural identities of the novel molecules 7-9 were straightforwardly established on the basis of elemental analysis, IR, multinuclear (1H, 13C, 29Si) NMR spectroscopy, and UV-visible and mass spectrometry. For 7 and 8, the 1H NMR spectra show the characteristic pattern for monosubstituted ferrocenes, specifically, two pseudotriplets and a singlet for the cyclopentadienyl rings of 7 and three pseudotriplets and a singlet for the cyclopentadienyl ligands of 8. Regarding the vinyl group, both compounds show, in either CDCl3 or (CD3)2CO solution, three doublets of doublets in the expected integrated ratios, which are consistent with an AMX system. In analogy with the 1H NMR spectra, increased symmetry from 8 to 7 simplifies the cyclopentadienyl region in the 13C NMR spectra. Consequently, the 13C NMR spectrum of 7 shows only three resonances, while in compound 8 the number of cyclopentadienyl signals is six, with the ipso-carbon at 68.9 ppm. 1H NMR of 9 in CDCl3 shows the expected signals for this

compound, namely, a set of signals for the vinyl groups, two signals for the ferrrocenyl groups, and a signal for the methyl groups. However, if (CD3)2CO is used as solvent, both 1H and 13C NMR spectra of compound 9 are rather complicated, as doubling of the cyclopentadienyl, methyl, and vinyl resonances can be observed, resulting in two series of close and identical signals (see, for instance, Figure 1). This complex pattern of signals can be related to the presence of two stereogenic silicon centers, and it is consistent with a mixture of two diastereomers.30 Unfortunately, all attempts of separation of optically pure diastereomers using different HPLC chiral columns, as well as different eluents, have been unsuccessful so far. The 29Si NMR spectra of compounds 7 and 8 in CDCl3 showed the expected single resonance at -17.0 ppm and at -17.3 ppm, respectively. For 9 the 29Si NMR resonance shifted downfield, at -10.9 ppm. These 29Si NMR chemical shift resonances agree with the values found for other ferrocenyldisiloxanes.31 As expected, the 29Si NMR spectrum of 9 in (CD3)2CO also gave evidence for the presence of two diastereomers since two close signals were observed at -10.82 and -10.83 ppm (see Figure S8 in Supporting Information). On the other hand, the IR spectra of 8 and 9 exhibit strong Si-O stretching vibrations, characteristic of Si-O-Si disiloxane linkages, namely, at 1084 cm-1 for 8 and at 1034 cm-1 for 9. Mass spectral analysis of 7-9 confirmed the proposed structures, showing the corresponding molecular ions Mþ at m/z 610.1 (for 7), at m/z 866.0 (for 8), and at m/z 526.1 (for 9), together with some less intense peaks assignable to reasonable fragmentation products. X-ray Structures of 7, 8, and 9. In order to identify unambiguously the proposed structures, single-crystal X-ray diffraction studies of the three vinyl-containing ferrocenyl (30) An example of diastereomeric divinyldisiloxane-1,3-diol with two asymmetric silicon centers has been reported: Lee, M. E.; Cho, H. M.; Kang, D. J.; Lee, J.-S.; Kim, J. H. Organometallics 2002, 21, 4297. (31) Angelakos, C.; Zamble, D. B.; Foucher, D. A.; Lough, A. J.; Manners, I. Inorg. Chem. 1994, 33, 1709.

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Table 1. Selected Crystallographic Data for Compounds 7, 8, and 9 7 empirical formula fw temp, K wavelength, A˚ cryst syst space group a, A˚ b, A˚ c, A˚ R, deg β, deg γ, deg V, A˚3 Z density (calcd), mg m-3 F(000) no. of reflns collected no. of indep reflns completeness no. of data/restraints/params goodness-of-fit on F2 R1, wR2 (I >2σ(I)) R1, wR2 (all data) largest diff peak and hole, e A˚-3

8

C32H30Fe3Si 610.20 monoclinic P21/n 7.704(3) 16.295(5) 20.126(6) 90 99.551(8) 90 2491.4(15) 4 1.627 1256 35 655 4734 [R(int) = 0.0642] 99.5% (to θ = 25.72°) 4734/0/325 1.046 0.0308, 0.0615 0.0493, 0.0704 0.421 and -0.309

9

C44H42Fe4OSi2 866.36 100(2) 0.71073 triclinic P1 8.432(1) 9.948(1) 11.992(1) 109.368(5) 105.461(5) 94.265(7) 899.9(2) 1 1.599 446 42 901 4624 [R(int) = 0.0492] 99.3% (to θ = 28.70°) 4624/0/316 1.089 0.0222, 0.0590 0.0277, 0.0627 0.326 and -0.304

C26H30Fe2OSi2 526.38 triclinic P1 7.591(2) 14.408(3) 23.510(6) 73.749(10) 83.146(8) 78.529(8) 2413.8(9) 4 1.448 1096 31 203 8756 [R(int) = 0.0476] 98.7% (to θ = 25.37°) 8756/6/597 1.082 0.0447, 0.1044 0.0761, 0.1268 0.925 and -0.612

Table 2. Selected Bond Lengths (A˚) and Angles (deg) for Compounds 7 and 8 lengths

7

8

angles

7

8

Fe(1)-C(3) Fe(2)-C(13) Fe(3)-C(23) Si(1)-C(3) Si(1)-C(13) Si(1)-C(23) Si(1)-C(1) Si(1)-O(1) C(1)-C(2) Fe(1)-Fe(2) Fe(1)-Fe(3) Fe(2)-Fe(3) Fe(1)-Fe(1A) Fe(1)-Fe(2A) Fe(2)-Fe(2A)

2.059(3) 2.051(3) 2.037(3) 1.847(3) 1.846(3) 1.846(3) 1.849(3)

2.0524(14) 2.0593(13)

Si(1)-C(3)-Fe(1) Si(1)-C(13) -Fe(2) Si(1)-C(23) -Fe(3) C(3)-Si(1)-C(1) C(13)-Si(1)-C(1) C(23)-Si(1)-C(1) C(23)-Si(1)-C(3) C(13)-Si(1)-C(3) C(2)-C(1)-Si(1) Si(1) -O(1) -Si(1A) O(1)-Si(1)-C(3) O(1)-Si(1)-C(13) O(1)-Si(1)-C(1)

129.10(14) 128.51(14) 127.93(14) 111.35(13) 112.93(12) 110.66(13) 107.34(12) 108.41(12) 125.8(2)

126.23(7) 129.04(7)

1.310(4) 6.033 5.942 6.195

1.8509(15) 1.8502(14) 1.8492(18) 1.6187(4) 1.317(3) 5.993 7.998 6.527 9.648

Table 3. Selected Bond Lengths (A˚) and Angles (deg) for Compound 9 9A Fe(1)-C(7) Fe(2)-C(17) Si(1)-C(7) Si(2)-C(17) O(1)-Si(1) O(1)-Si(2) Fe(1)-Fe(2) Si(1)-C(7)-Fe(1) Si(2)-C(17)-Fe(2) Si(2)-O(1)-Si(1) O(1)-Si(1)-C(7) O(1)-Si(2)-C(17)

2.052(4) 2.057(4) 1.840(5) 1.853(5) 1.641(3) 1.627(3) 7.639 126.5(2) 123.8(2) 143.2(2) 109.70(18) 110.60(19)

9B Fe(3)-C(33) Fe(4)-C(43) Si(3)-C(33) Si(4)-C(43) O(2)-Si(3) O(2)-Si(4) Fe(3)-Fe(4) Si(3)-C(33)-Fe(3) Si(4)-C(43)-Fe(4) Si(3)-O(2)-Si(4) O(2)-Si(3)-C(33) O(2)-Si(4)-C(43)

2.051(4) 2.045(4) 1.859(5) 1.841(5) 1.628(3) 1.642(3) 7.555 123.7(2) 127.4(2) 142.9(2) 110.95 108.84(18)

molecules 7-9 were undertaken. Crystals of 7 and 8 suitable for X-ray diffraction were obtained at -30 °C from a solution of the corresponding compound in hexane/CH2Cl2 (10:2). Single crystals of 9 were obtained by slow evaporation from a solution of 9 in hexane, at room temperature. A summary of crystallographic data and data collection parameters is included in Table 1. Tables 2 and 3 contain a comparison of selected bond lengths and angles of compounds 7-9.

111.13(7) 112.43(7)

128.36(14) 180.00(2) 108.51(5) 108.91(5) 107.45(6)

Triferrocenylvinylsilane (7) crystallizes in the monoclinic space group P21/n with Z=4. The molecular structure of 7 is illustrated in Figure 2. The X-ray analysis of 7 showed that each of the three ferrocenyl groups is arranged in a relatively perpendicular orientation to one another. The cyclopentadienyl rings are eclipsed in two of the ferrocenyl units, while in the third they are arranged, approximately, in a conformation between eclipsed and staggered. The silicon atom is nearly tetrahedral with C-Si-C bond angles between 112.93(12)° and 107.34(12)°. The ferrocenyl units are separated by 5.942, 6.033, and 6.195 A˚ Fe- - -Fe distances. Bond lengths and bond angles, summarized in Table 2, are reasonable and typical of other ferrocenylsilanes such as 2, 3, and 6,19,24a being in particular similar to those reported for chlorotriferrocenylsilane, ClSi[(η5-C5H4)Fe(η5-C5H5)]3, which was structurally characterized by Manners et al.32 Confirmation of the tetrametallic structure of 8 was obtained by single-crystal X-ray diffraction. Compound 8 crystallizes in the triclinic P1 space group with Z = 1. Figure 3A shows that in each siloxane moiety the two bulky (32) MacLachlan, M. J.; Zheng, J.; Thieme, K.; Lough, A. J.; Manners, I.; Mordas, C.; LeSuer, R.; Geiger, W. E.; Liable-Sands, L.-M.; Rheingold, A. L. Polyhedron 2000, 19, 275.

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Figure 2. Molecular structure of triferrocenylvinylsilane (7). Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms have been omitted for clarity.

ferrocenyl groups linked to the silicon are disposed in an orthogonal arrangement, probably to avoid steric congestion around the silicon atom. Remarkably, the Si-O-Si disiloxane skeleton of 8 is linear; Si-O-Si angle=180.0(2)°. This angle value is significantly greater than the Si-O-Si angle found in related disiloxane 9 (see below) and the Si-O-Si angle of 157.1(3)° reported by Manners for tetraferrocenyldisiloxanediol, [OHSi(Fc)2]2O.29a The large SiO-Si angle for 8 is probably imposed by the steric hindrance of the two ferrocenyl units linked to the same silicon atom.33,34 If molecule 8 is viewed along the Si-O-Si axis (Figure 3B), the substituents on the silicon atoms are disposed in a stable, fully staggered structure, with the ferrocene (Fe1) trans to ferrocene (Fe1A), ferrocene (Fe2) trans to ferrocene (Fe2A), and the two vinyl groups trans to one another. The Fe atoms of the ferrocenyl substituents attached to the same silicon center are separated by 5.993 A˚. Likewise, the iron centers of the ferrocenyl units attached to different silicon atoms are separated by 6.527 A˚ (for the cisferrocenyl groups) as well as 7.998 and 9.648 A˚ (for the transferrocenyl groups). From these values, iron-iron interactions are expected to be most significant for ferrocenyl moieties linked to the same silicon atom. Compound 9 crystallizes in the triclinic P1 space group with Z = 4. The two independent molecules in the asymmetric unit cell (9A and 9B) are shown in Figure 4A and B, respectively. Molecules 9A and 9B differ only slightly in their bond lengths and bond angles. In both molecules, the two ferrocenyl groups attached to the silicon atoms are disposed (33) A related example of a diferrocenyl molecule also possessing a linear Si-O-Si group is the disiloxane-bridged [1]ferrocenophane [(η5C5H4)2Fe(Me2Si)]2O reported by Wrackmeyer, Herberhold, and coworkers: Wrackmeyer, B.; Ayazi, A.; Milius, W.; Herberhold, M. J. Organomet. Chem. 2003, 682, 180. (34) It is well known that the Si-O-Si bond angle is very sensitive to subtle effects, and the variation in the values of the Si-O-Si angles has been the subject of theoretical and experimental studies. See for example: (a) Shambayati, S.; Blake, J. F.; Wierschke, S. G.; Jorgensen, W. L.; Schreiber, S. L. J. Am. Chem. Soc. 1990, 112, 697. (b) Sheldrick, W. S. In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, U.K., 1989; Chapter 3.

Figure 3. (A) Molecular structure of 1,3-divinyl-1,1,3,3-tetraferrocenyldisiloxane (8). (B) Projection along the Si-O-Si unit for 8. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms have been omitted for clarity.

in a nearly parallel arrangement. This arrangement is different from that observed by Pannell et al. in the structure of [(Fc)Si(Me)2]2O, in which the two ferrocenyl units are disposed in a more typical orthogonal arrangement.35 The cyclopentadienyl rings in 9 are essentially parallel and essentially eclipsed in both ferrocenyl moieties. In sharp contrast to tetrametallic compound 8 having a linear Si-O-Si skeleton, the bimetallic 9 shows a bent arrangement of the disiloxane linkage, and the Si-O-Si angle was found to be 143.2(2)° for 9A and 142.9(2)° for 9B, as a result of the reduced level hindrance by the methyl substituents. The intramolecular Fe- - -Fe separation distance is 7.639 A˚ for 9A and 7.555 A˚ for 9B (Table 3). A view down the Si-O-Si bridge, Figure 4C, indicates that there is a staggered conformation of all the silicon substituents, presumably to facilitate the Fe- - -Fe interaction. Electrochemical Studies of 7, 8, and 9. The anodic electrochemistry of the vinyl-functionalized compounds 7, 8, and 9 containing three, four, and two ferrocenyl moieties, respectively, was examined by cyclic voltammetry (CV) and square (35) Cervantes-Lee, F.; Sharma, H. K.; Pannell, K. H.; DerecskeiKovacs, A.; Marynick, D. S. Organometallics 1998, 17, 3701.

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Figure 4. (A and B) Structures of the two independent molecules (labeled 9A and 9B) of 1,3-divinyl-1,3-dimethyl-1,3-diferrocenyldisiloxane (9). (C) Projection along the Si-O-Si linkage for 9. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms have been omitted for clarity. Table 4. Electrochemical Data for Si-Vinyl-Functionalized Polyferrocenyl Compoundsa compound 3 6 7 8 9

1

E1/2

0.376 (0.450) 0.410 (0.420) 0.436 (0.400)c 0.428 (0.411)c 0.472 (0.484)

2

E1/2

0.668 (0.630) 0.750 (0.590) 0.736 (0.568)c 0.624 (0.500)c 0.656 (0.592)

3

E1/2

1.048 (0.704)c 0.892 (0.676)c

4

E1/2

1.108

ΔE (2E1/2 - 1E1/2)b 292 (180) 340 (170) 300 (168) 196 (89) 184 (108)

ΔE (3E1/2 - 2E1/2)b

312 (136) 268 (176)

ΔE (4E1/2 - 3E1/2)b

216

a

E1/2 in V vs SCE, determined by square wave voltammetry in CH2Cl2 solution (unless otherwise noted), with [n-Bu4N][B(C6F5)4] or [n-Bu4N][PF6] for values indicated in parentheses as supporting electrolytes. b Peak potential separation values, ΔE, are given in mV. c In CH2Cl2/CH3CN (1:0.5) solution.

wave voltammetry (SWV) using dichloromethane as nonnucleophilic solvent. The half-wave potentials (E1/2) of the electrochemical processes described below are summarized in Table 4, together with those of related Si-vinyl- and

Si-allyl-functionalized compounds 3 and 6, measured in the same medium. One of the most interesting features of compound 9 is the presence of two ferrocenyl redox-active moieties linked

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Figure 5. Cyclic voltammograms (left) and square wave voltammetric responses (right) of dichloromethane solutions of [(CH2dCH)(Fc)MeSi]2O (9) also containing (A and B) 0.1 M [n-Bu4N][PF6] and (C and D) 0.1 M [n-Bu4N][B(C6F5)4]. CVs are at a scan rate of 0.1 V s-1.

together in close enough proximity, through a short disiloxane bridge. This simple molecule can serve as an interesting model compound for investigating electronic interactions between two organometallic units linked by a saturated three-atom bridging system. To the best of our knowledge, the only studies so far reported concerning the electrochemical behavior of compounds having ferrocenyl groups separated by disiloxane units have been described by Manners and co-workers for hexaferrocenylcyclotrisiloxane, [Fc2SiO]3, which was synthesized by base-catalyzed condensation of diferrocenylsilanediol, Fc2Si(OH)2.29a For this remarkable cyclic hexametallic molecule, differential pulse voltammetric studies, using benzonitrile as solvent, showed several partially overlapped, poorly resolved oxidation waves. As seen in Figure 5A, in dichloromethane solution with the traditional supporting electrolyte tetra-n-butylammonium hexafluorophosphate ([n-Bu4N][PF6]), the cyclic voltammogram of biferrocenyl 9 shows two closely spaced voltammetric waves. Since the two waves are severely overlapped, oxidation potentials were further estimated by square wave voltammetry of 9, which shows better resolution of the two redox processes (Figure 5B). The first oxidation process, at 1 E1/2 =þ0.484 V (SCE), corresponds to the oxidation of one of the neutral ferrocenyl subunits, resulting in the formation of monocationic species 9þ. At a higher potential (2E1/2 = þ0.592 V), the second ferrocenyl subunit is oxidized, giving the dicationic compound 92þ. For redox-active multimetallic compounds, the magnitude of the separation between the half-wave potentials (ΔE1/2) of two redox sites present in the molecule has usually been taken as a measure of electronic interaction between (36) For leading references on the dependence of ΔE1/2 values in organometallic compounds on different experimental conditions, such as temperatures, solvents, and electrolytes, see: (a) Barriere, F.; Geiger, W. E. J. Am. Chem. Soc. 2006, 128, 3980. (b) Nadafy, A.; Chin, T. T.; Geiger, W. E. Organometallics 2006, 25, 1654. (c) Barriere, F.; Camire, N.; Geiger, W. E.; Mueller-Westerhoff, U. T.; Sanders, R. J. Am. Chem. Soc. 2002, 124, 7262. (d) LeSuer, R. J.; Geiger, W. E. Angew. Chem., Int. Ed. 2000, 39, 248. (e) Camire, N.; Mueller-Westerhoff, U. T.; Geiger, W. E. J. Organomet. Chem. 2001, 637-639, 823.

metals.1,2,5 However, one should be extremely careful when using electrochemical data since voltammetric separations are influenced by the effects of the solvent/supporting electrolyte media, which can modify the electrostatic interactions in polycationic species.14,36 With the aim of estimating how the supporting electrolyte affects the ΔE1/2 values of 9, we have studied the anodic electrochemistry of this disiloxane-bridged biferrocenyl compound in dichlorometane solution, also containing tetra-n-butylammonium tetrakis(pentafluorophenyl)borate ([n-Bu4N][B(C6F5)4]) as supporting electrolyte. When B(C6F5)4- is used as electrolyte anion, the CV of 9 (Figure 5C) exhibits two perfectly resolved, reversible anodic waves. For both redox couples, the plot of peak current versus v1/2 (v = scan rate) was linear, indicating that redox processes were diffusion controlled. Likewise, the square wave voltammogram shows two well-separated oxidations (Figure 5D). Clearly, in agreement with the results reported by Geiger and co-workers,36 the combination of CH2Cl2 and [n-Bu4N][B(C6F5)4] as solvent/electrolyte medium provides more favorable conditions for electrochemical studies of polyferrocenyl compounds, minimizing ion-pairing interactions between the [B(C6F5)4]- electrolyte anion and the cationic products generated in the oxidation processes. Consequently, as compared to the [PF6]- anion, the [B(C6F5)4]- electrolyte anion has a lower coordinating power and restrains ion pairing, allowing development of interactions between the two metallocene units in 9. This results in the observation of one-electron oxidation waves, at different potentials, for each of the ferrocenyl moieties appended at both ends of the disiloxane link. The presence of two, well-separated, oxidation processes for bimetallic molecule 9 is consistent with the existence of appreciable iron-iron electronic interactions between the two ferrocenyl redox sites linked to different silicon atoms in the Si-O-Si bridge. Thus, after the first ferrocenyl center was oxidized, at 1E1/2 = þ0.472 V (SCE), the potential required to oxidize the remaining neutral ferrocene center increases (2E1/2 = þ0.656 V), resulting in dicationic compound 92þ. This twowave redox response can be qualitatively related to that found by Manners, Geiger, and co-workers,11 and Pannell

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Figure 6. Cyclic (left) and square wave (right) voltammetric behavior, on Pt electrode, of [(CH2dCH)(Fc)2Si]2O (8) in (A) CH2Cl2/ 0.1 M [n-Bu4N][PF6]; (B and C) CH2Cl2/CH3CN (5:1 by volume) with 0.1 M [n-Bu4N][PF6]; and (D and E) CH2Cl2/0.1 M [n-Bu4N][B(C6F5)4]. CVs are at a scan rate of 0.1 V s-1.

and co-workers,12 in oligo- and polyferrocenylsilanes in which, unlike in the case of 9, the interacting ferrocenyl moieties are linked to the same silicon atom. The straightforward determination of the two redox potentials for the two ferrocenyl moieties for 9 allowed the determination of the comproportionation constant, Kc, relative to the equilibrium among the three oxidation states of the two iron atoms in 9, described by eq 1. The value of Kc can be obtained as Kc = exp[FΔE1/2/RT].37 f½FeII - Si- O- Si- ½FeII g þ f½FeIII - Si- O- Si- ½FeIII g2þ f 2f½FeII - Si- O- Si- ½FeIII gþ

ð1Þ

The wave splitting (ΔE1/2 = E1/2 - E1/2) between the two redox events (for compound 9, ΔE1/2 = 184 mV in CH2Cl2/ [n-Bu4N][B(C6F5)4]) and the comproportionation constant (Kc) are both representative of the thermodynamic stability of the mixed valence state in 9 relative to other redox systems. From the electrochemical viewpoint, based on the resulting value of Kc =1.29 103, the partially oxidized molecule [9]þ belongs to the slightly delocalized class II mixed-valence species, according to the Robin-Day classification.38 Although the use of ΔE1/2 potential separation provides only a primary marker with regard to electronic communication between redox centers,36a comparison of the ΔE1/2 value of compound 9 with those shown by other related silicon-bridged biferrocenyl derivatives in the same solvent/ electrolyte medium provides a qualitative estimation of the electronic interaction extent between the ferrocenyl subunits. Thus, measured in CH2Cl2/[n-Bu4N][PF6], the wave splitting 2

1

(37) Richardson, D. E.; Taube, H. Inorg. Chem. 1981, 20, 1278. (38) (a) Robin, M. B.; Day, P. Adv. Inorg. Chem. Radiochem. 1967, 10, 247. (b) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1.

for Si-O-Si disiloxane-bridged compound 9 (ΔE1/2 =108 mV) is smaller than the ΔE1/2 value for bis(ferrocenyl)vinylmethylsilane (3) (ΔE1/2 = 180 mV) and the value for bis(ferrocenyl)dimethylsilane (Fc(SiMe2)Fc) (ΔE1/2 =150 mV).11a Nevertheless, the ΔE1/2 value for 9 is slightly larger than that observed by Pannell et al. for Fc(SiMe2)3Fc,12b containing a three-atom Si-Si-Si bridge (ΔE1/2 = 80 mV in CH2Cl2/ [n-Bu4N][PF6]). These data suggest that the extent of ironiron electronic communication is somewhat higher when the two ferrocenyl moieties are linked by the three-atom SiO-Si bridging group than by the three-atom Si-Si-Si bridging group. Clearly, the four ferrocenyl redox moieties of tetrametallic compound 8 also provide an excellent opportunity to study multistep electron-transfer processes. Figure 6 compares the electrochemical response of divinyldisiloxane 8 in several media. The CV of 8 in CH2Cl2/0.1 M [n-Bu4N][PF6] (Figure 6A) exhibits a sequence of several overlapped oxidations from about 0.40 to 0.70 V (SCE), which have coupled reverse features. The oxidation wave present at more anodic potential is not a diffusion-controlled process at all the potential scan rates investigated. This indicates that for compound 8, with four ferrocenyl units, a change in solubility accompanies the change in oxidation state, so that upon scan reversal after the oxidation process, the reduction wave gave rise to a sharp cathodic peak. Thus, the full oxidation of 8 results in the precipitation of electrogenerated tetracationic species 84þ onto the electrode surface, and on the reverse scan, this tetraoxidized cation is redissolved as it is reduced. However, when a small amount of acetonitrile is added to the CH2Cl2 electrolyte medium, the cathodic stripping peak disappears (see Figure 6B), and the CV of 8 shows several overlapped waves having diffusional features. Likewise, square wave voltammetric measurements for 8, in CH2Cl2/CH3CN

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Scheme 3. Electrochemical Behavior of Tetraferrocenyldisiloxane 8

(5:1 by volume), exhibit three slightly separated oxidation events (see Figure 6C). The third peak is broader than the first two, suggesting that this wave involves two unresolved one-electron processes. To better clarify the redox behavior of tetraferrocenyl compound 8, we also used [n-Bu4N][B(C6F5)4] as supporting electrolyte in dichloromethane solution. In Figure 6D and E it becomes patently obvious that improved electrochemical reversibility and better resolution are achieved if [B(C6F5)4]is employed as electrolyte anion (instead of [PF6]-). With [B(C6F5)4]-, no electrode adsorption effects were observed, which is indicative of a better solubility of the tetraferrocenium electrogenerated oxidation product 84þ in this solvent/ electrolyte medium. As a result, the CV of 8 clearly shows four perfectly resolved, reversible anodic oxidation waves. In the same way, the square voltammogram of Figure 6D clearly shows how the four ferrocenyl-based oxidations of compound 8 spread out when this electrolyte is used. The E1/2 values for the four one-electron-transfer processes of 8 are given in Table 4. Specifically, the ΔE1/2 = 4E1/2 - 1E1/2 potential separation value goes from 265 mV with the traditional electrolyte [n-Bu4N][PF6] to 680 mV in the weakly coordinating supporting electrolyte [n-Bu4N][B(C6F5)4]. The considerable spread of the four oxidations in tetraferrocenyl 8 suggests significant interactions between the four ferrocenyl units as they are oxidized successively. The mechanism for the electrochemical oxidation of compound 8 is suggested to consist of four consecutive one-electrontransfer steps, as shown in Scheme 3. The first oxidation (at 1E1/2 = 0.428 V (SCE) with [B(C6F5)4]- as electrolyte anion) corresponds to the generation of monocationic species 8þ, by oxidation of one of the neutral ferrocenyl units in the disiloxane bridge. At a higher potential (2E1/2 = 0.624 V), a second electron is removed from a ferrocenyl moiety attached to the neighboring silicon atom, at the other end of the Si-O-Si bridge, yielding the dicationic tetraferrocenyl species 82þ. The potential difference between the first two oxidations in 8, 2E1/2 - 1E1/2 = 196 mV, is similar to the redox separation between ferrocenyl groups in 9. On the other hand, the potential separation between the second and third redox processes, ΔE1/2 = 3E1/2 - 2E1/2 =268 mV, is larger than the 2E1/2 - 1E1/2 and 4E1/2 3 E1/2 values (see Table 4). On this basis, it follows that the third oxidation of 9 (at 3E1/2 = 0.892 V) occurs at one of the two ferrocenyl moieties adjacent to an already oxidized

ferrocenyl subunit. The final oxidation of the remaining neutral ferrocenyl center, neighboring those already oxidized, is the most difficult and takes place at more anodic potential (4E1/2 = 1.108 V), giving the tetracationic species 84þ. As far as 7 is concerned, the CV scan of this trisferrocenyl molecule, in CH2Cl2 with [n-Bu4N][PF6], proceeds in three well-resolved oxidations steps. The third, more anodic, wave (Ep =0.704 vs SCE) is not a diffusion-controlled process and exhibits a typical stripping peak as its cathodic counterpart (see Figure S12 in the Supporting Information). This indicates that tricationic species 73þ precipitates on the electrode surface. Nevertheless, measured in CH2Cl2 with [n-Bu4N][B(C6F5)4], the CV of 7 shows three well-defined and reversible (chemically and electrochemically) one-electron steps (Figure 7A), suggesting strong electronic interactions between all three iron centers as they are successively oxidized. Likewise, the corresponding square wave voltammogram (Figure 7B) shows three well-separated redox processes at E1/2 = 0.436, 0.736, and 1.048 V vs SCE due to the redox couples 7/7þ, 7þ/72þ, and 72þ/73þ, respectively. As expected, the potential difference between the first two oxidation processes (2E1/2 - 1E1/2 = 300 mV) is slightly smaller than that recorded between the last two (3E1/2 - 2E1/2 = 312 mV). Comparison of the redox potentials found for 7 with those measured for the related dendrimer precursor 3 (2E1/2 - 1E1/2 = 292 mV in CH2Cl2/[n-Bu4N][B(C6F5)4]) shows that the attachment of a third ferrocenyl unit to the vinylsilane group increases slightly the interactions between the metal centers.

Concluding Remarks A new series of Si-vinyl-functionalized molecules 7, 8, and 9, in which three, four, and two ferrocenyl substituents, respectively, are linked by a silicon or a disiloxane bridge, have been synthesized by the methathesis reaction of monolithioferrocene and the chlorosilanes (CH2dCH)SiCl3 and [(CH2dCH)(Cl)MeSi]2O. Electrochemical studies indicated that for tetraferrocenyl 8 and biferrocenyl 9 the three-atom Si-O-Si disiloxane linkage affords a considerable degree of electronic communication between the ferrocenyl centers, as reflected by the observed splitting of the voltammetric waves for their one-electron oxidations. The reactive -Si-CHd CH2 functionality in compounds 7-9 opens interesting possibilities for further synthetic elaboration, in order to construct highly branched dendritic structures (dendrimers

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Figure 7. Cyclic voltammogram (A) and square wave voltammetry (B) of (CH2dCH)Si(Fc)3 (7) in CH2Cl2 solution also containing 0.1 M [n-Bu4N][B(C6F5)4]. CV is at a scan rate of 0.1 V s-1.

and dendronized polymers). We are currently exploring this chemistry. Likewise, reactivity studies of the hydrosilylation reactions of the bifunctional disiloxanes 8 and 9 with 1,1,3,3tetramethyldisiloxane and 1,10 -bis(dimethylsilyl)ferrocene are in progress in our laboratory and will be published in the near future.

Experimental Section Materials and Equipment. All reactions and compound manipulations were performed in an oxygen- and moisture-free atmosphere (N2 or Ar) using standard Schlenk techniques. Solvents were dried by standard procedures over the appropriate drying agents and distilled immediately prior to use. Ferrocene (Aldrich) was purified by sublimation prior to use. tert-Butyllithium (1.7 M solution in pentane) and n-butyllithium (2.5 M solution in hexane) (Aldrich) were used as received. (Tri-n-butylstannyl) chloride, trichlorovinylsilane (Aldrich), and 1,3-divinyl-1,3-dimethyl-1,3-dichlorodisiloxane (ABCR) were distilled prior to use. Silica gel (70-230 mesh) (Aldrich) was used for column chromatographic purifications. (Tri-n-butylstannyl)ferrocene was synthesized as described in the literature.39 Infrared spectra were recorded on Bomem MB-100 FT-IR and on Perkin-Elmer 100 FT-IR spectrometers. A Unicam V-410 spectrophotometer was used to obtain UV-visible measurements. NMR spectra were recorded on Bruker-AMX-300 and Bruker DRX-500 spectrometers. Chemical shifts were reported in parts per million (δ) with reference to residual solvents resonances for 1H and 13C NMR (CDCl3, 1H, δ 7.27 ppm; 13C, δ 77.0 ppm and (CD3)2CO, 1 H, δ 2.09 ppm; 13C, δ 205.9 and 30.6 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 dithranol. Samples were prepared in CH2Cl2 or hexane. Elemental analyses were performed by the Microanalytical Laboratory, SIDI, Universidad Aut onoma de Madrid, Spain. (39) Guillaneux, D.; Kagan, H. B. J. Org. Chem. 1995, 60, 2502.

Bru~ na et al. Electrochemical Measurements. Cyclic voltammetric and square wave voltametric experiments were recorded on a BASCV-50W potentiostat. CH2Cl2 and CH3CN (spectrograde) for electrochemical measurements were freshly distilled from calcium hydride under argon. The supporting electrolytes used were tetra-n-butylammonium hexafluorophosphate (Fluka), which was purified by recrystallization from ethanol and dried under vacuum at 60 °C, and tetra-n-butylammonium tetrakis(pentafluorophenyl)borate, which was synthesized as described in the literature,40 by metathesis of [NBu4]Br with Li[B(C6F5)4] 3 (nOEt2) (Aldrich) in methanol and recrystallized twice from CH2Cl2/hexane. The supporting electrolyte concentration was typically 0.1 M. A conventional three-electrode cell connected to an atmosphere of prepurified nitrogen was used. 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) (both Bioanalytical Systems), each of which were polished on a Buehler polishing cloth with Metadi II diamond paste, rinsed thoroughly with purified water and acetone, and dried under vacuum. All potentials were referenced to the saturated calomel electrode (SCE). Under our conditions, the decamethylferrocene redox couple [FeCp*2]0/þ is -0.056 V vs SCE in CH2Cl2/0.1 M [n-Bu4N][PF6]. A coiled platinum wire was used as a counter electrode. Solutions were 10-3 M in the redox-active species. The solutions for the electrochemical experiments were purged with nitrogen and kept under an inert atmosphere throughout the measurements. Square wave voltammetry was performed using frequencies of 10 Hz. X-ray Crystal Structure Determination. Compounds 7, 8, and 9 were structurally characterized by single-crystal X-ray diffraction. Suitable orange crystals of 7, 8, and 9 of dimensions 0.25 0.08 0.06, 0.20 0.10 0.10, and 0.20 0.08 0.04 mm, respectively, were located and mounted on a glass fiber with “magic oil”. The samples were transferred to a Bruker SMART 6K CCD area-detector three-circle diffractometer with a MacScience rotating anode (Cu KR radiation, λ = 1.54178 A˚) generator equipped with Goebel mirrors at settings of 50 kV and 100 mA. For compound 7 a total of 4734 independent reflections (Rint = 0.0642) were colleted in the range 1.62° < θ < 25.72°. For compound 8 a total of 4624 independent reflections (Rint = 0.0492) were colleted in the range 2.32° < θ < 28.70°. For compound 9 a total of 8756 independent reflections (Rint = 0.0476) were collected in the range 0.90° < θ < 25.37°. X-ray data were collected at 100 K, with a combination of six runs at different j and 2θ angles, 3600 frames. Data were collected using 0.3° wide ω scans with a crystal-to-detector distance of 4.0 cm. The substantial redundancy in data allows empirical absorption corrections (SADABS)41 to be applied using multiple measurements of symmetry-equivalent reflections. Raw intensity data frames were integrated with the SAINT program,42 which also applied corrections for Lorentz and polarization effects. The software package SHELXTL version 6.10 was used for space group determination, structure solution, and refinement.43 The space group determination was based on a check of the Laue symmetry and systematic absences and was confirmed using the structure solution. The structures were solved by direct methods (SHELXS-97), completed with difference Fourier syntheses, and refined with full-matrix least-squares using SHELXL-97 minimizing w(Fo2 - Fc2)2.44,45 Weighted R factors (Rw) and all goodness of fit S are based on F2; conventional R factors (R) are based on F. All non-hydrogen atoms were (40) LeSuer, R. J.; Buttolph, C.; Geiger, W. E. Anal. Chem. 2004, 76, 6395. (41) Sheldrick, G. M. SADABS Version 2.03, Program for Empirical Absorption Correction; University of G€ottingen: Germany, 1997-2001. (42) SAINTþNT Version 6.04; SAX Area-Detector Integration Program; Bruker Analytical X-ray Instruments: Madison, WI, 1997-2001. (43) Bruker AXS. SHELXTL Version 6.10, Structure Determination Package; Bruker Analytical X-ray Instruments: Madison, WI, 2000.

Article refined with anisotropic displacement parameters. The hydrogen atom positions were calculated geometrically and were allowed to ride on their parent carbon atoms with fixed isotropic U. All scattering factors and anomalous dispersion factors are contained in the SHELXTL 6.10 program library. The crystal structures of 7, 8, and 9 have been deposited at the Cambridge Crystallographic Data Centre and allocated the deposition numbers CCDC 770888, 770889, and 770890, respectively. Synthesis of (CH2dCH)Si(Fc)3 (7) and [(CH2dCH)(Fc)2Si]2O (8). Ferrocenyllithium was generated in situ via the reaction of (tri-n-butylstannyl)ferrocene (20.0 g, 42.1 mmol) with n-butyllithium (19.0 mL, 2.5 M solution in hexane) in 55 mL of THF at -78 °C. After 90 min, the mixture was warmed to -40 °C. To this stirred system was added dropwise trichlorovinylsilane (1.6 mL, 12.6 mmol) in 20 mL of THF. The mixture was allowed to warm to room temperature and was stirred overnight. The solution was concentrated, treated with hexane, and then filtered to remove the lithium chloride byproduct. Solvent removal yielded a red-orange, oily product, which was chromatographed on a 3 cm 26 cm of silica gel column. A first band containing ferrocene was eluted using hexane as eluent. Subsequently, a second major orange band was eluted using a mixture of hexane/ CH2Cl2 (100:15). Solvent removal afforded the desired compound 7 as an analytically pure, air-stable, orange crystalline solid. Finally, on eluting with hexane/CH2Cl2 (100:20) a third band was collected. Solvent removal afforded the secondary reaction product 8, which was obtained as an analytically pure, air-stable, orange crystalline solid. 7: Yield: 3.23 g (42%). Anal. Calcd for C32H30SiFe3: C, 62.95; H, 4.96. Found: C, 62.68; H, 4.98. 1H NMR (CDCl3, 300 MHz): δ 4.05 (s, 15H, C5H5), 4.25, 4.39 (m, 12H, C5H4), 6.08 (dd, 3J = 20.2 Hz, 2J=4.0 Hz, 1H, CHdCHtrans Hcis), 6.25 (dd, 3J=14.7 Hz, 2J = 4.0 Hz, 1H, CHdCHtrans Hcis), 6.69 (dd, 3J = 20.2 Hz, 3 J=14.7 Hz, 1H, CHdCH2). 13C{1H} NMR (CDCl3, 75 MHz): δ 68.7 (C5H5), 70.8, 74.0 (C5H4), 133.2 (CHdCH2), 136.4 (CHdCH2). 29Si{1H} NMR (CDCl3, 59 MHz): δ -17.0 (SiFc). IR (KBr): ν(CdC) 1163 cm-1, ν(Si-C) 820 cm-1. UV-vis (CH2Cl2): λmax 450 nm. MS (MALDI-TOF): m/z 610.1 [Mþ], 425.1 [Mþ - 1Fc]. 8: Yield: 0.82 g (15%). Anal. Calcd for C44H42OSi2Fe4: C, 60.97; H, 4.89. Found: C, 60.69; H, 4.92. 1H NMR (CDCl3, 300 MHz): δ 4.08 (s, 20H, C5H5), 4.16, 4.22 (m, 8H, C5H4), 4.35 (m, 8H, C5H4), 6.09 (dd, 3J = 20.1 Hz, 2J = 4.1 Hz, 2H, CHdCHtrans Hcis), 6.19 (dd, 3J = 15.0 Hz, 2J = 4.1 Hz, 2H, CHdCHtrans Hcis), 6.52 (dd, 3J = 20.1 Hz, 3J = 15.0 Hz, 2H, CHdCH2). 13C{1H} NMR (CDCl3, 75 MHz): δ 68.6 (C5H5), 68.9, 70.9, 71.0, 73.7, 74.0 (C5H4), 133.4 (CHdCH2), 137.5 (CHdCH2). 29Si{1H} NMR (CDCl3, 59 MHz): δ -17.3 (44) Sheldrick, G. M. Acta Crystallogr. A 1990, 46, 467. (45) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refinement; University of G€ottingen: Germany, 1997.


2807

(SiFc). IR (KBr): ν(CdC) 1161 cm-1, ν(Si-O-Si) 1084 cm-1, ν(Si-C) 818 cm-1. UV-vis (CH2Cl2): λmax 449 nm. MS (MALDI-TOF): m/z 866.0 [Mþ]. Synthesis of [(CH2dCH)(Fc)MeSi]2O (9). A 15 g amount of ferrocene (80.63 mmol) was dissolved in a mixture of 130 mL of dry THF and 40 mL of dry hexane, under argon at room temperature, and then cooled to -25 °C. To this stirred system was added dropwise a 1.5 M solution of t-BuLi in pentane (23.71 mL, 40.31 mmol). The mixture was stirred another 30 min and warmed to -10 °C before a solution of 1,3-divinyl-1,3dimethyl-1,3-dichlorodisiloxane (4.25 g, 18.14 mmol) in 10 mL of dry THF was added dropwise. The mixture was allowed to slowly warm to room temperature and was stirred overnight. The solution was concentrated, treated with hexane, and then filtered to remove the lithium chloride byproduct. Solvent removal yielded an orange solid, which was purified by column chromatography on silica gel (3 cm 30 cm) using hexane as eluent. A first band containing ferrocene was eluted, and subsequently, a second major orange band was eluted with hexane/ THF (100:0.5). Solvent removal afforded the desired product 9 as an analytically pure, air-stable, orange crystalline solid. Yield: 5.25 g (55%). Anal. Calcd for C26H30Si2OFe2: C, 59.31; H, 5.75. Found: C, 58.96; H, 5.68. 1H NMR ((CD3)2CO, 500 MHz): δ 0.424 (s, 6H, CH3), 0.422 (s, 6H, CH3), 4.14 (m, 12H þ 12H, C5H5 and C5H4), 4.17 (m, 2H þ 2H, C5H4), 4.38 (m, 4H þ 4H, C5H4), 5.90 (dd, 3J = 20.4 Hz, 2J = 3.9 Hz, 2H þ 2H, CHdCHtrans Hcis), 6.064 (dd, 3J = 14.8 Hz, 2J = 3.9 Hz, 2H, CHdCHtrans Hcis), 6.062 (dd, 3J = 14.8 Hz, 2J = 3.9 Hz, 2H, CHdCHtrans Hcis), 6.39 dd, 3J = 20.4 Hz, 3J = 14.8 Hz, 2H, CHdCH2), 6.37 (dd, 3J=20.4 Hz, 3J=14.8 Hz, 2H, CHdCH2). 13 C{1H} NMR ((CD3)2CO, 125 MHz): δ -1.09, -1.10 (CH3), 68.2 (C5H5), 69.10, 69.11, 70.89, 70.97, 72.86, 72.88, 73.05 (C5H4), 131.91, 131.92 (CHdCH2), 138.66, 138.68 (CHd CH2). 29Si{1H} NMR ((CD3)2CO, 59 MHz): δ -10.82, -10.83 (SiFc). IR (KBr): ν(CdC) 1165 cm-1, ν(Si-O-Si) 1034 cm-1 ν(Si-C) 820 cm-1. UV-vis (CH2Cl2): λmax 448 nm. MS (MALDI-TOF): m/z 526.1 [Mþ].

Acknowledgment. We gratefully acknowledge the financial support provided by the Spanish Ministerio de Ciencia e Innovaci on, Project CTQ2009-09125/BQU. S.B. acknowledges the Spanish Ministerio de Educaci on y Ciencia for a FPU grant. We would like to thank Prof. Angel E. Kaifer (University of Miami) and Prof. Antonio Anti~ nolo (Universidad de Castilla la Mancha) most sincerely for their helpful discussions. Supporting Information Available: Complete X-ray crystallographic data for compounds 7, 8, and 9 (CIF files), NMR and mass spectra (MALDI-TOF) for 7-9, and additional CV for 7. This material is available free of charge via the Internet at http:// pubs.acs.org.

Vinyl-Functionalized Silanes and Disiloxanes with Electronically

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