Organometallics 2010, 29, 6157–6160 DOI: 10.1021/om100889w
6157
Half-Sandwich (η6-Arene)iron(II) Dinitrogen Complexes Bearing a Disilaferracycle Skeleton as a Precursor for Double Silylation of Ethylene and Alkynes Yusuke Sunada,*,†,‡ Tsuyoshi Imaoka,‡ and Hideo Nagashima†,‡ †
Institute for Materials Chemistry and Engineering and ‡Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan Received September 15, 2010
Summary: Reaction of 2 equiv of 1,2-bis(dimethylsilyl )benzene with [Fe(mesityl)2]2 in aromatic solvent under a nitrogen atmosphere afforded the dinuclear bis(silyl)iron complexes [(η6-arene)Fe(Me2SiC6H4SiMe2)]2( μ-η1:η1-N2) (1), which have an end-on-bound bridging dinitrogen ligand. The dinitrogen unit easily dissociated from the Fe center to generate the mononuclear (η6-arene)FeII(Si)2L or (η6-arene)FeIV(Si)2H2 complexes by the reactions with CO, PPh3, and H2. It is well-known that η6-arene ligands contribute to stabilizing certain transition-metal complexes, providing a wide range of electronic and steric environments to the metal center.1 Among the η6-arene metal compounds, half-sandwich Ru(II) complexes of the type (η6-arene)RuX2L (L = two-electron-donor ligand) are undeniably the most studied ones. A few halfsandwich Ru(IV) complexes have also been investigated, which
are interesting in relation to the reactions involving Ru(II)/ Ru(IV) redox.2 They have received considerable attention in particular from the point of view of catalysis; a number of useful catalytic reactions have taken part in the progress of organic and polymer synthesis over the last three decades.3 The successful chemistry of (η6-arene)RuII complexes strongly indicates that studies on their iron analogues (η6-arene)FeX2L should provide unique reactions and catalysis; however, studies on (η6-arene)Fe complexes are surprisingly rare. There are only a few examples of (η6-arene)FeX2L complexes;4 for instance, Pomeroy et al. have described the synthesis of (η6-arene)Fe(SiCl3)2(CO) by the reaction of Fe(SiCl3)2(CO)4 with arenes at 210 °C.4a For (η6-arene)FeIV compounds, unique (η6-arene)Fe(H)2(SiCl3)2 complexes were reported by Klabunde; however, their preparation was only achieved by metal vapors in quite low yield, which is not accessible without using a special apparatus.5 We have been involved in the organometallic chemistry of disilametallacycles. In particular, those prepared from a metal precursor and 1,2-bis(dimethylsilyl)benzene are stable and were characterized with ease.6 In this paper, we wish to report new access to disilaferracyclopentenes bound to η6arene ligands, which are unprecedentedly formed by the reaction of Floriani’s coordinatively unsaturated [Fe(mesityl)2]2 (mesityl = 2,4,6-Me3C6H2) complex7 with 1,2-bis(dimethylsilyl)benzene in aromatic solvents. Dinuclear dinitrogen complexes, [(η6-arene)Fe(Me2SiC6H4SiMe2)]2( μ-η1:η1-N2) (1), were isolated from the reaction mixture, providing the following three novel aspects in organoiron chemistry. First, a bridging dinitrogen ligand was easily replaced by
*To whom correspondence should be addressed. E-mail: sunada@ cm.kyushu-u.ac.jp. (1) (a) Severin, K. Chem. Commun. 2006, 3859–3867. (b) Therrien, B. Coord. Chem. Rev. 2009, 253, 493–519. (c) Gastinger, R. G.; Klabunde, K. J. Transition Met. Chem. 1979, 4, 1–13. (d) Moriarty, R. M.; Gill, U. S.; Ku, Y. Y. J. Organomet. Chem. 1988, 350, 157–190. (e) Bennett, M. A. Coord. Chem. Rev. 1997, 166, 225–254. (f ) Brunner, H. Eur. J. Inorg. Chem. 2001, 905–912. (g) Werner, H. Angew. Chem., Int. Ed. Engl. 1983, 22, 927–949. (h) Zelonka, R. A.; Baird, M. C. Can. J. Chem. 1972, 50, 3063– 3072. (i) Suss-Fink, G. Dalton Trans. 2010, 39, 1673–1688. ( j) Yan, Y. K.; Melchart, M.; Habtemariam, A.; Sadler, P. J. Chem. Commun. 2005, 4764– 4776. (2) (a) Djurovich, P. I.; Carroll, P. J.; Berry, D. H. Organometallics 1994, 13, 2551–2553. (b) Djurovich, P. I.; Dolich, A. R.; Berry, D. H. J. Chem. Soc., Chem. Commun. 1994, 16, 1897–1998. (c) Mbaye, M. D.; Demerseman, B.; Renaud, J.-L.; Toupet, L.; Bruneau, C. Adv. Synth. Catal. 2004, 346, 835–841. (d) Albers, M. O.; Liles, D. C.; Robinson, D. J.; Shaver, A.; Singleton, E. J. Chem. Soc., Chem. Commun. 1986, 645–647. (e) Albers, M. O.; Liles, D. C.; Robinson, D. J.; Shaver, A.; Singleton, E. Organometallics 1987, 6, 2347–2354. (f ) Gruber, S.; Zaitsev, A. B.; W€orle, M.; Pregosin, P. S. Organometallics 2008, 27, 3796–3805. (g) Kondo, H.; Yamaguchi, Y.; Nagashima, H. Chem. Commun. 2000, 1075–1076. (h) Nagashima, H.; Mukai, K.; Itoh, K. Organometallics 1984, 3, 1314–1315. (i) Nagashima, H.; Mukai, K.; Shiota, Y.; Yamaguchi, K.; Ara, K.; Fukahori, T.; Suzuki, H.; Akita, M.; Moro-oka, Y.; Itoh, K. Organometallics 1990, 9, 799– 807. ( j) Kondo, H.; Kageyama, A.; Yamaguchi, Y.; Haga, M.; Kirchner, K.; Nagashima, H. Bull. Chem. Soc. Jpn. 2001, 74, 1927–1937. (3) (a) Noyori, R. Angew. Chem., Int. Ed. 2002, 41, 2008–2022. (b) Carmona, D.; Lamata, M. P.; Oro, L. A. Coord. Chem. Rev. 2000, 200-202, 717–772. (c) Diaz-Alvarez, A. E.; Crochet, P.; Zablocka, M.; Duhayon, C.; Cadierno, V.; Gimeno, J.; Majoral, J. P. Adv. Synth. Catal. 2006, 348, 1671– 1679. (d) Tse, M. K.; D€obler, C.; Bhor, S.; Klawonn, M.; M€agerlein, W.; Hugl, H.; Beller, M. Angew. Chem., Int. Ed. 2004, 43, 5255–5260. (e) Sandoval, C. A.; Bie, F.; Matsuoka, A.; Yamaguchi, Y.; Naka, H.; Li, Y.; Kato, K.; Utsumi, N.; Tsutsumi, K.; Ohkuma, T.; Murata, K.; Noyori, R. Chem. Asian J. 2010, 5, 806–816. (f ) Hashiguchi, S.; Fujii, A.; Takehara, J.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1995, 117, 7562–7563. (g) Stumpf, A. W.; Saive, E.; Demonceau, A.; Noels, A. F. J. Chem. Soc., Chem. Commun. 1995, 1127–1128. (h) Zhou, H.; Li, Z.; Wang, Z.; Wang, T.; Xu, L.; He, Y.; Fan, Q.; Pan, J.; Gu, L.; Chan, A. S. C. Angew. Chem. 2008, 120, 8592–8595.
(4) For examples of iron(II) (η6-arene)FeX2L and related complexes, see: (a) Hansen, V. M.; Batchelor, R. J.; Einstein, F. W. B.; Male, J. L.; Pomeroy, R. K.; Zaworotko, M. J. Organometallics 1997, 16, 4875– 4881. (b) Kubo, H.; Hirano, M.; Komiya, S. J. Organomet. Chem. 1998, 556, 89–95. (c) Schneider, J. J.; Hagen, J.; Czap, N.; Kr€uger, C.; Mason, S. A.; Bau, R.; Ensling, J.; G€utlich, P.; Wrackmeyer, B. Chem. Eur. J. 2000, 6, 625– 635. (d) Begley, M. J.; Puntambekar, S. G.; Wright, A. H. J. Organomet. Chem. 1989, 362, C11–C14. (e) Schneider, J. J.; Hagen, J.; Czap, N.; Bl€aser, D.; Boese, R.; Ensling, J.; G€utlich, P.; Janiak, C. Chem. Eur. J. 2000, 6, 468– 474. (5) For examples of iron(IV) (η6-arene)Fe(Si)2(H)2 complexes, see: (a) Yao, Z.; Klabunde, K. J.; Asirvatham, A. S. Inorg. Chem. 1995, 34, 5289–5294. (b) Yao, Z.; Klabunde, K. J. Inorg. Chem. 1997, 36, 2119–2123. (c) Yao, Z.; Klabunde, K. J.; Hupton, A. C. Inorg. Chim. Acta 1997, 259, 119–124. (d) Asirvatham, A. S.; Yao, Z.; Klabunde, K. J. J. Am. Chem. Soc. 1994, 116, 5493–5494. (e) Yao, Z.; Klabunde, K. J. Organometallics 1995, 14, 5013–5014. (6) Sunada, Y.; Fujimura, Y.; Nagashima, H. Organometallics 2008, 27, 3502–3513. (7) Klose, A.; Solari, E.; Ferguson, R.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Organometallics 1993, 12, 2414.
r 2010 American Chemical Society
Published on Web 11/11/2010
pubs.acs.org/Organometallics
6158
Organometallics, Vol. 29, No. 23, 2010
Sunada et al.
Scheme 1
two-electron-donor ligands to give facile access to (η6-arene)Fe(SiR3)2L, including an analogue of Pomeroy’s (η6-arene)Fe(SiCl3)2(CO). Second, treatment of 1 with H2 provided the first example of the oxidative addition reaction of disilaferra(II)cyclopentenes to form the stable disilaferra(IV)cyclopentenes 4, as a new analogue of Klabunde’s (η6-arene)Fe(H)2(SiCl3)2. Third, reactions of 1 with alkenes and alkynes led to elimination of disilacarbocycles, which were reportedly obtained by stoichiometric as well as catalytic reactions of disilametallacyclopentenes with alkenes and alkynes.8,9 Although the reaction is not catalytic at present, it is important that the reactions which have occurred so far on the precious metals especially on platinum can be achieved with iron. Treatment of 2 equiv of 1,2-bis(dimethylsilyl)benzene with [Fe(mesityl)2]2 in benzene at 65 °C for 16 h under a nitrogen atmosphere afforded a mixture of compounds, including the diamagnetic dinuclear Fe(II) dinitrogen complex [(η6C6H6)Fe(Me2SiC6H4SiMe2)]2( μ-η1:η1-N2) (1a). Careful recrystallization of this mixture resulted in separation of 1a from paramagnetic impurities; 1a in pure crystalline form was isolated in 26% yield. The analogous complex 1b, in which η6-toluene is coordinated to the iron center, was prepared in a similar fashion in 28% isolated yield (Scheme 1). The complex 1a is diamagnetic in pure form, giving sharp NMR signals. 1H and 13C resonances of 1a due to the η6benzene ligand were found at δ 4.30 and 88.1 ppm, respectively. The signals due to the SiMe2 groups appeared as two singlets at 0.34 and 0.97 ppm in the 1H NMR spectrum, whereas two carbon resonances were seen at δ 6.8, 7.8 ppm in the 13C NMR spectrum. The 29Si{1H} NMR spectrum of 1a showed a singlet at δ 42.8 ppm. These spectral features indicate that the two Me2Si groups are magnetically equivalent, whereas the two Me moieties on each Si atom are inequivalent. The NMR data of 1b are similar to those of 1a, except that the η6-toluene ligand gives four 1H signals (ortho, para, meta-H, and Me) and five 13C resonances (ortho, para, meta, ipso-C, and Me). The Raman spectrum of 1a,b showed a strong absorption band derived from the bridging N2 moiety at 2035 cm-1 for 1a and 2022 cm-1 for 1b, which is consistent with weak back-donation from the (8) For Pt-catalyzed double silylation, see: (a) Tanaka, M.; Uchimaru, Y.; Lautenschlager, H.-J. J. Organomet. Chem. 1992, 428, 1–12. (b) Tanaka, M.; Uchimaru, Y.; Lautenschlager, H. -J. Organometallics 1991, 10, 16–18. (c) Shimada, S.; Tanaka, M.; Honda, K. Inorg. Chim. Acta 1997, 265, 1–8. (d) Uchimaru, Y.; Brandi, P.; Tanaka, M.; Goto, M. J. Chem. Soc., Chem. Commun. 1993, 744–745. (e) Shimada, S.; Uchimaru, Y.; Tanaka, M. Chem. Lett. 1995, 223–224. (f ) Tanaka, M.; Uchimaru, Y. Bull. Soc. Chim. Fr. 1992, 129, 667–675. (9) Ni- or Pd-catalyzed double silylation have also been reported. For instance, see: (a) Kang, S. O.; Lee, J.; Ko, J. Coord. Chem. Rev. 2002, 231, 47–65. (b) Naka, A.; Okazaki, S.; Hayashi, M.; Ishikawa, M. J. Organomet. Chem. 1995, 499, 35–41. (c) Naka, A.; Okada, T.; Ishikawa, M. J. Organomet. Chem. 1996, 521, 163–170. (d) Kang, Y.; Lee, J.; Kong, Y. K.; Kang, S. O.; Ko, J. Organometallics 2000, 19, 1722–1728.
Figure 1. Molecular structures of 1b (left) and 3b (right) showing 50% probability ellipsoids. Hydrogen atoms are omitted for clarity.
metal to the coordinated N2 (cf. νNtN of free dinitrogen at 2331 cm-1).10 The molecular structures of 1a,b were confirmed to be dinuclear by X-ray diffraction analysis.11 The ORTEP drawing of 1b is depicted in Figure 1 as a representative. Bond distances and angles of 1a,b are summarized in the Supporting Information. A dinitrogen ligand is connecting two iron centers in an end-on fashion, being linearly assembled to each iron center. The N-N bond lengths of 1.119(3) A˚ for 1a and 1.126(3) A˚ for 1b are comparable to those observed in the previously reported Fe(II) dinitrogen complexes,12 which are close to the N-N distance of the free dinitrogen molecule (1.0977 A˚).10 The Fe-N bond lengths of 1.81 A˚ are similar to those reported for Fe(II) dinitrogen complexes. Each iron center adopts a three-legged piano-stool coordination geometry with an η6-arene ligand as a seat. The disilylbenzene unit forms a disilaferra(II)cyclopentene. The distances of the iron atom to the centroid of the arene ring are 1.5866(12) and 1.5844(12) A˚ for 1a and 1.5888(13) A˚ for 1b. The fact that the N-N bond distance and the νNtN stretching frequency of 1 are not very different from those of uncoordinated N2 suggest that the dinitrogen molecule is not strongly bound to the iron center. Indeed, the dinitrogen ligand in 1a,b was easily replaced by two molecules of CO or PPh3 to give the corresponding mononuclear disilaferracyclic compounds at room temperature, as shown in Scheme 2. An X-ray structure determination of the CO complex 2a and phosphine complexes 3a,b showed that the iron center of 2a and 3 adopts the three-legged piano-stool coordination geometry with one arene ligand as the seat and two Si atoms and one CO or PPh3 ligand as the legs. 1 H and 13C NMR data of 2a,b and 3a,b are in accord with those deduced from the molecular structures. In a typical example, the 1H NMR spectrum of 3a shows two magnetically inequivalent SiMe2 signals at 0.54 and 0.92 ppm and a singlet due to the η6-benzene ligand at 4.84 ppm. In the 13C (10) MacKay, B. A.; Fryzuk, M. D. Chem. Rev. 2004, 104, 385–402. (11) CCDC 787773 (1a), 787774 (1b), 787775 (2a), 787776 (3a), 787777 (3b), and 787778 (4a) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam. ac.uk/data_request/cif. (12) (a) Hills, A.; Hughes, D. L.; Jimenez-Tenorio, M.; Leigh, G. J. J. J. Organomet. Chem. 1990, 391, C41–C44. (b) Crossland, J. L.; Young, D. M.; Zakharov, L. N.; Tyler, D. R. Dalton Trans. 2009, 9253–9259. (c) Wiesler, B. E.; Lchnert, N.; Tuczek, F.; Neuhausen, J.; Tremel, W. Angew. Chem., Int. Ed. 1998, 37, 815–817. (d) de la Jara Leal, A.; Tenorio, M. J.; Puerta, M. C.; Valerga, P. Organometallics 1995, 14, 3839–3847. (e) MacBeth, C. E.; Harkins, S. B.; Peters, J. C. Can. J. Chem. 2005, 83, 332–340. (f ) Mankad, N. P.; Whited, M. T.; Peters, J. C. Angew. Chem., Int. Ed. 2007, 46, 5768–5771. (g) Whited, M. T.; Mankad, N. P.; Lee, Y.; Oblad, P. F.; Peters, J. C. Inorg. Chem. 2009, 48, 2507–2517. (h) Ohki, Y.; Hatanaka, T.; Tatsumi, K. J. Am. Chem. Soc. 2008, 130, 17174–17186.
Communication
Organometallics, Vol. 29, No. 23, 2010
6159
Scheme 2
Scheme 3 Figure 2. Molecular structure of 4a showing 50% probability ellipsoids. Hydrogen atoms, except that on Fe, are omitted for clarity.
NMR spectrum of 3a, a singlet appears at δ 87.7 ppm which is assignable to the η6-benzene moiety. A singlet is found at 65.9 ppm in the 31P resonance of 3a. The molecular structure and spectroscopic data of the carbonyl complexes are interesting in comparison with those of Pomeroy’s (η6-arene)Fe(SiCl3)2(CO). The carbonyl complex 2a has a structure analogous to that of (η6-arene)Fe(SiCl3)2(CO); the distance between the centroid of the arene ˚ ) is 0.05-0.1 A˚ shorter, ring and Fe center in 2a (1.60 A whereas the Fe-Si bond distances of 2a are significantly elongated (ca. 0.05-0.1 A˚). The 13C resonances, δco =209.8 ppm in 2a and 210.4 ppm in 2b, are slightly (ca. 3 ppm) shifted to lower field in comparison with Pomeroy’s complexes.4a The IR spectrum of 2a and 2b is characteristic in giving CtO stretching bands at 1910 cm-1 for 2a and 1907 cm-1 for 2b. The CO stretching absorption of Pomeroy’s (η6-arene)Fe(SiCl3)2(CO) was found at 2001 cm-1 for the η6-benzene complex and 1996.5 cm-1 for the η6-toluene analogue,4a which are shifted ca. 90 cm-1 to higher frequencies compared to those of 2a,b. The back-donation from iron to the π* orbital of CO in 2 is apparently stronger than that in (arene)Fe(SiCl3)2(CO). These features suggest a stronger electron donating property of the 1,2-bis(dimethylsilyl)benzene moiety than the two SiCl3 groups. Facile dissociation of the bridging N2 ligand from the iron centers also realized the successful oxidative addition of H2. A benzene solution of 1a was stirred under a hydrogen atmosphere for 16 h at room temperature. The initial orange color of the solution changed to pale yellow. Slow evaporation of the solvent afforded the Fe(IV) dihydride complex 4a in 96% yield (Scheme 3). Similarly, the η6-toluene derivative of 4a was obtained in 93% yield by the reaction of 1b with H2 in toluene. The molecular structure of 4a was determined by an X-ray diffraction analysis. Figure 2 shows the ORTEP drawing of 4a, and bond distances and angles are given in the Supporting Information. Complex 4a adopts a four-legged pianostool coordination geometry with the η6-benzene ligand as a seat. Two hydride ligands were detected from the Fourier map and are located trans to each other. The long H-H and Si-H distances of 4a (2.183 A˚ for H-H, 2.014-2.101 A˚ for Si-H) preclude any H-H and/or Si-H interaction.
Although the Fe-H bond distances (1.47(3) and 1.48(2) A˚) are comparable, there are significant differences in the Fe-Si and Fe-arene(centroid) bond distances between 4a and Klabunde’s complex: the Fe-Si bond distances of 2.2852(6) and 2.2937(6) A˚ in 4a are significantly longer than those of Klabunde’s complex (2.210(3) and 2.207(3) A˚ for (η6arene)Fe(SiCl3)2(H)2), whereas the distance from the Fe to the center of the benzene ligand in 4a (1.5552(11) A˚) is ca. 0.05 A˚ shorter.5a This large difference is presumably due to the electronic properties of the Si ligand: 1,2-bis(dimethyl)benzene strongly donates the electron density to the iron center, whereas SiCl3 acts as an electron-withdrawing π-acceptor ligand. The 1H NMR spectrum of 4a in C6D6 shows one singlet for the SiMe2 group at δ 0.77 ppm and a singlet at δ -18.0 ppm for the Fe-H group with an integral ratio of 12:2, which is consistent with the four-legged piano-stool coordination geometry having trans-dihydride. The chemical shift for the coordinated benzene protons is δ 4.77, which is shifted ca. 0.5 ppm to lower field in comparison with the starting complex 1a. The 13C resonance due to the η6-benzene ligand of 4a appears at δ 87.6 ppm, which shows a ca. 10 ppm higher field shift compared with that of Klabunde’s complex. A singlet was found at 31.1 ppm in the 29Si NMR, which exhibits a high-field shift relative to that of 1a, reflecting the increase of the oxidation state of the iron. The trans configuration of dihydride resulted in high thermal stability of 4a, which did not eliminate either H2 or 1,2-bis(dimethylsilyl)benzene even at 80 °C. In sharp contrast, (η6arene)Fe(SiCl3)2(H)2 reportedly started to decompose at 57 °C concomitant with the release of HSiCl3.5a Although either an η2-dihydrogen or a cis-dihydride species may exist as the intermediate to form 4a from 1a, attempts to detect them by NMR at low temperature have so far been unsuccessful. One of the interesting aspects of disilametallacycle chemistry is the chemical transformation of organosilyl moieties on the metal. Tanaka and co-workers reported the reactions of a disilaplatinacyclopentene complex with alkenes and alkynes to give disilacarbocycles.8 The facile replacement of the dinitrogen ligand of 1 by two-electron-donor ligands described above actually led to reactions of 1 with alkenes and alkynes. Treatment of 1a with ethylene (1 atm) resulted in 1,2- and 1,1-double silylation to form 5 and 6 in a ratio of 2:3 in 87% yield (Scheme 4). No intermediate was detectable in the 1H NMR spectrum, and the “(arene)Fe” fragment was decomposed to form iron black. Similarly, 2-butyne and
6160
Organometallics, Vol. 29, No. 23, 2010 Scheme 4
phenylacetylene reacted with 1a to form the double-silylated products 7a,b in quantitative yield at 40 °C for 14 h. Interestingly, trimerization of the alkyne used was observed in addition to the disilacarbocycle formation. It is important that this disilacarbocycle formation is a rare example of the reaction of disilaferracycles;13 in fact, we confirmed that Fink’s famous iron(II) carbonyl complex (Me2SiC6H4SiMe2)Fe(CO)414 was completely inert in the reactions with (13) As a special case, an iron carbonyl complex mediated cycloaddition reaction of a structurally and electronically peculiar disilabutane, 1,1,2,2-tetrafluoro-1,2-disilacyclobutane, with 1,3-cyclohexadiene to afford the disilacarbocycle have been reported by Liu et al. Although the product is similar to our reaction, Liu’s reaction is different from ours in that this was triggered by the release of the ring strain. See: (a) Lin, C. H.; Lee, C. Y.; Jzang, T. T.; Lin, C. C.; Liu, C. S. J. Organomet. Chem. 1988, 356, 325–342. (b) Lin, C. H.; Lee, C. Y.; Liu, C. S. Organometallics 1987, 6, 1869–1878. (c) Lin, C. H.; Lee, C. Y.; Liu, C. S. J. Am. Chem. Soc. 1986, 108, 1323–1325. (14) (a) Fink, W. Helv. Chim. Acta 1975, 58, 1464–1465. (b) Fink, W. Helv. Chim. Acta 1976, 59, 606–613. (15) One of the reviewers suggested the possibility of [Fe(mesityl)2]2 as a catalyst to form the double-silylated products. To confirm this, we performed the reaction of 2-butyne or phenylacetylene with 1,2-bis(dimethylsilyl)benzene in the presence of [Fe(mesityl)2]2 (20 mol % for Fe) under the same conditions; however, only trace amounts of doublesilylated products were obtained.
Sunada et al.
ethylene or 2-butyne at 120 °C in a sealed tube. The disilaplatinacyclopentenes catalyze the reactions of 1,2-bis(dimethylsilyl)benzene with alkenes or alkynes at temperatures between 30 and 110 °C.8 In a similar fashion, 1 could be a catalyst of a similar transformation. However, attempted reactions of 1,2-bis(dimethylsilyl)benzene with ethylene, 2-butyne, and phenylacetylene in the presence of a catalytic amount of 1 resulted in iron black formation after formation of a stoichiometric amount of the disilacarbocycle.15 Nevertheless, it is important that the reactions which have so far been achieved by precious metals such as platinum have become realized by iron. In summary, we have synthesized the novel dinuclear halfsandwich Fe(II) complexes 1 as the first (η6-arene)FeIIX2L complexes bearing a weakly coordinated ligand. This complex provides easy access to (η6-arene)Fe(Si)2L and (η6arene)Fe(Si)2(H)2, whereas reactions with alkenes and alkynes result in the stoichiometric production of disilacarbocycles. The result shown here is a good entry to the unexplored chemistry of half-sandwich (η6-arene)Fe complexes, and active studies are underway.
Acknowledgment. This work was supported by Grant No. 18064014 (Priority Area ”Synergy of Elements“) and Grant No. 22750055 (Young Scientists (B)) from the Ministry of Education, Culture, Sports, Science and Technology of Japan and the JGC-S Scholarship Foundation (Y.S.). We thank Prof. Dr. Hiroki Ago and Mr. Takafumi Ayagaki at Kyushu University for their kind support in measuring the Raman spectra. Supporting Information Available: Text, tables, figures, and CIF files giving a detailed experimental section, the molecular structures of 1a,b, 2a, 3a,b, and 4a, and details of crystallographic studies. This material is available free of charge via the Internet at http://pubs.acs.org.
