Cymantrene- and Ferrocene-Based Complexes with Perfluorinated

Max Roemer, Peter Schmiel, and Dieter Lentz*. Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstrasse 34-36,...
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Cymantrene- and Ferrocene-Based Complexes with Perfluorinated Bridging Moieties Max Roemer, Peter Schmiel, and Dieter Lentz* Institut f€ur Chemie und Biochemie, Anorganische Chemie, Freie Universit€at Berlin, Fabeckstrasse 34-36, 14195 Berlin, Germany

bS Supporting Information ABSTRACT: Trifluorovinylcymantrene (1) and -ferrocene (2) form the basis of a versatile building block chemistry. Di- and trinuclear complexes with perfluorinated bridging moieties are obtained by [2þ2] cycloaddition on 1 and nucleophilic substitution on the C2F3 unit of 2 with cymantrenyllithium.

’ INTRODUCTION Introduction of fluorinated chains into cp rings of metal organic complexes alters dramatically the reactivity, spectroscopic and electrochemical behavior. Their syntheses remain a synthetic challenge today. Despite numerous publications on cyclopentadienyl transition metal complexes, their derivatives with perfluorinated side chains have drawn relatively little but increasing attention so far. This is probably due to the fact that cyclopentadienes with perfluorinated side chains like trifluoromethylcyclopentadiene1 are challenging to obtain. Only a few publications deal with trifluoromethyl cyclopentadienyl complexes, including cymantrene2 and ferrocene derivatives.2,3 Derivatives with tetramethyl trifluoromethyl cp ligands were reported, too.4 Several cyclopentadienyl transition metal complexes with various fluorous alkyl chain substiuents were  ermak et al.5 and Hughes et al.6 These compounds reported by C were prepared by syntheses of the respective fluorinated cyclopentadienes in the first step and reactions to the metal complexes in the second step. Additionally, (CH2)2-Rf8 substituents have been introduced into the cp ring of cymantrene by Negishi-type coupling reactions, starting from bromocymantrenes.7 Enhanced fluorophilicity is seen as a great potential of this type of molecule for possible applications as catalysts in fluorous media. The straightforward synthesis of pentafluorophenyl-substituted cyclopentadienes from routinely available starting materials allowed detailed studies of several transition metal complexes,8 although ferrocene derivatives containing perfluoroaryl substituents have been synthesized earlier by indirect methods.9 Beside these examples, ferrocenes with pentafluoropropenyl and 1,10 -bis(pentafluoropropenyl) groups were reported.10 Recently, we reported an effective synthesis and some reactions of trifluorovinylferrocene (2).11 Herein, we describe a straightforward synthesis of trifluorovinylcymantrene (1) by a similar Stille-type coupling12 strategy. Furthermore, we demonstrate a versatile building block chemistry by using the trifluorovinyl group as a synthetic functional group on 1 and 2. r 2011 American Chemical Society

Scheme 1. Synthesis of 1 by a Stille-Type Coupling Reaction

Scheme 2. Thermal [2þ2] Cycloaddition of 1

’ RESULTS AND DISCUSSION Trifluorovinylcymantrene (1) was obtained from a crosscoupling reaction of iodocymantrene and tributyltrifluorovinylstannane (Scheme 1). Due to our experience with 2, we chose the catalyst system Me-Phos/Pd(OAc)2 in DMF for the synthesis, as it gave the highest yields in comparison to other electron-rich phosphine ligands such as S-Phos,13 X-Phos,13 Dave Phos,13 and John Phos13 or triphenyl phosphine in DMF solution. Column chromatography on silica and distillation under vacuum yields 1 as a lemon yellow oil with a yield of 58%. Received: January 5, 2011 Published: March 21, 2011 2063

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Figure 3. ORTEP15 diagram of the molecular structure of 4. Ellipsoids are drawn at a probability level of 50%. Figure 1. ORTEP15 diagram of the molecular structure of 3a. Ellipsoids are drawn at a probability level of 50%.

Figure 2. ORTEP15 diagram of the molecular structure of 3b. Ellipsoids are drawn at a probability level of 50%.

Scheme 3. Reaction of 2 with Cymantrenyllithium

The trifluorovinyl group allows further modifications. Upon heating, 1 undergoes the expected [2þ2] cycloaddition reaction, which leads to the formation of a perfluorinated cyclobutane ring, a reaction observed for 211 and other fluoroalkenes14 (Scheme 2). The reaction is regioselective; only the head-tohead dimers are formed; no head-to-tail dimers could be detected by 19F NMR spectroscopy. According to the 19F NMR spectrum, the cis- and transisomers (3a,b) were obtained in equimolar quantities. 19F NMR spectra of 3a and 3b should exhibit signals of an AA0 BB0 CC0 spin system. However, one observes an AB-type spectrum for the CF2 groups, as all coupling constants except the geminal one seem to be extremely small. The CF groups are observed as singlets. The geminal coupling constants 2JFF 231 (3a) and 222 Hz (3b) appear in the expected range for

fluorinated cyclobutane derivatives. Both isomers could not be separated by column chromatography or crystallization. Nevertheless, crystallization from pentane afforded an excess of the cisisomer 3a in the crystalline material (3a:3b = 2:1), leaving an excess of 3b in the solution. In the 13C{1H} NMR spectra of the mixtures of isomers five resonances could be detected for the cyclopentadienyl carbon atoms of each isomer and a single resonance for the carbonyl carbon atoms at 222.72 and 223.06 ppm, respectively. However, resonances of the cyclobutane carbon atoms could not be detected, as coupling to the chemically and magnetically inequivalent fluorine atoms results in the distribution of the signal intensity on numerous signals. The needle-shaped crystals of 3a could be separated from the platelets of 3b using a microscope, allowing the structure determination by X-ray diffraction. Both rings are in puckered conformations; torsion angles (C6C7C8C9) are 17.67° for 3a and 15.09° for 3b, respectively. In 3a, the cp rings are nearly facing each other. (E)-1-Cymantrenyl-2-ferrocenyl-1,2-difluoroethene (4) could be obtained using a nucleophilic substitution reaction of cymantrenyllithium, prepared from cymantrene and n-butyllithium with 2 in THF (Scheme 3). The 19F NMR spectrum of 4 exhibits the expected AB pattern of a 1,2-disubstituted fluorinated ethane derivative. The 3J(19F19F) coupling constant of 121 Hz indicates the trans position of the fluorine substituents. The 13C{1H} NMR spectrum exhibits seven resonances for the chemically inequivalent cyclopentadienyl carbon atoms, two doublets of doublets for the ethene unit, and a single resonance for the carbonyl carbon atoms. The product was isolated in the form of deep red crystals after column chromatographic workup and crystallization. In 4, the cp rings of cymantrene and the substituted one of ferrocene are lying almost ideally in a plane. Both metal centers are oriented in the same direction. The oligomer 5 was isolated in minor amounts as a byproduct. It is likely to be formed by a second lithiation in 1,3-position on the cymantrene cyclopentadienyl ring of 4, caused by unconsumed n-butyllithium. In the following step, a second nucleophilic substitution takes place, resulting in the formation of 5. Lithiation in 1,3-postion on the cp rings by n-butyllithium or other lithium organyls has not been reported so far. A similar arrangement of the ferrocene and cymantrene units as in 4 can be observed in the Cs symmetric molecule. The “bird-like” structure consists of a cymantrene center with its ferrocene “wings” in 1,3-position. The trinuclear complex with cp ligands, connected by unsaturated bridges in 1,3-position, is unique in organometallic chemistry. 2064

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Figure 4. ORTEP15 diagram of the molecular structure of 5. Ellipsoids are drawn at a probability level of 50%.

Together with 4 and its ferroceneferrocene analogue 1,2-diferrocenyl-1,2-difluoroethene,11 these complexes represent the first examples of di- and trinuclear cptransition metal complexes interconnected by noncyclic perfluorinated spacers.

’ CONCLUSION In summary, we developed a straightforward synthesis of 1 from readily available starting materials. The binuclear complexes 3a and 3b could be synthesized on the basis of 1 as a versatile reagent. Furthermore, an approach from its ferrocene counterpart 2 made the bi- and trinuclear complexes 4 and 5 accessible. ’ EXPERIMENTAL SECTION `All reactions were carried out under argon, using standard Schlenk and vacuum line techniques. THF was distilled from sodium/ benzophenone. DMF was distilled from calcium hydride. n-Bu3Sn-C2F3,16 (η5-C5H4I)Mn(CO)3,17 and 211 were prepared according to literature methods. Other substances were obtained commercially and used as received, without further purification. NMR spectra were recorded on a JEOL Lambda 400 and a Bruker 700 Avance 3 spectrometer in the case of the 13C NMR spectra of 3a, 3b, and 4. 1H and 13C NMR spectra were referenced to solvent signals; 19F NMR spectra were referenced externally to CFCl3. IR spectra were recorded on a Nicolet iS10 spectrometer with an ATR Smart Dura Sampl/IR device. Mass spectra were recorded on a MAT 711 spectrometer in electron impact mode (EI). 1: A Schlenk flask was charged with 500 mg (1.98 mmol) of iodocymantrene, 1.47 g (3.96 mmol) of tributyltrifluorovinylstannane, 182 mg (0.5 mmol) of Me-Phos, 22 mg (0.1 mmol) of palladium(II) acetate, and 1 mL of DMF. The flask was sealed and stirred at 70 °C for 12 h, followed by an aqueous workup with pentane. The organic phase was dried over sodium sulfate, and tin byproducts were removed by column chromatography on silica with pentane as eluent. Evaporation of the solvent afforded a yellow oil, which was then subjected to vacuum distillation, yielding 330 mg (1.14 mmol) of 1 (58%) as a yellow oil. 1 H NMR (CDCl3): δ 5.03, 4.78 (AA0 BB0 , 4 H, cp-H). 19F NMR (CDCl3): δ 98.1 (dd, 3J = 32 Hz, 2J = 72 Hz, 1F), 115.0 (dd, 2 J = 72 Hz, 3J = 112 Hz, 1F), 175.6 (dd, 3J = 32 Hz, 3J = 112 Hz, 1F). 13 C{1H,19F} NMR (CDCl3): δ 223.6 (CO), 152.1 (CF2), 124.1 (CF), 88.3, 82.1, 80.8. MS (EI): m/z (%) 284 (14) [M]þ, 228 (9) [C7H4F3Mn(CO)]þ, 200 (14) [C7H4F3Mn]þ, 176 (16) [C5H4F3Mn]þ, 107 (100) [C4H4Mn]þ. HRMS (EI): calcd 283.9493, found 283.9496. IR (neat): 569(m), 590(m), 626(s), 652(m), 674(m), 726(w), 836(m), 872(m), 905(w), 963(w), 999(m), 1039(w), 1072(m), 1121(w), 1159 (m), 1228(w), 1291(m), 1324(w), 1353(w), 1385(w), 1408(w), 1495 (w), 1637(w), 1773(s), 1916(s), 2020(s), 2850(w), 2930(w), 2960(w), 3122(w).

3a, 3b: 80 mg (0.28 mmol) of 1 was heated under inert conditions for 12 h at 110 °C. The resulting product mixture was dissolved in 5 mL of n-pentane, filtered through silica, and eluted with n-pentane. According to the 19F NMR spectrum the resulting solution contained a 1:1 mixture of the isomeric compounds 3a and 3b. Concentration of the solution to about 1 mL and crystallization at 4 °C yielded 34 mg (42%) of a mixture of 3a and 3b in a ratio of 2:1 as pale yellow crystals. Mechanical separation, using a microscope, afforded pale yellow needles of 3a and plates 3b. 3a: 1H NMR (C6D6): δ 4.09, 3.98, 3.61, 3.53 (ABCD, 8H, cp-H). 19F NMR (C6D6): δ 124.90 (d, 2J = 231 Hz, 2F); 129.53 (d, 2J = 231 Hz, 2F); 165.59 (s, 1F). 13C{1H} NMR (C6D6): δ 222.72 (CO), 87.93, 85.31, 82,72, 82.17, 80.80. MS (EI): m/z (%) 568 (100) [M]þ and smaller fragments. HRMS (EI): calcd 567.89860, found 567.89720. IR (neat): 534(s), 560(m), 602(s), 611(s), 627(s), 656(m), 670(m), 804(m), 827(m), 839(w), 846(w), 852(w), 861(w), 914(m), 955(w), 1017(w), 1028(w), 1051(w), 1070(w), 1078(w), 1098(w), 1147(w), 1178(m), 1197(m), 1238(w), 1272(w), 1280(w), 1315(w), 1341(w), 1375(w), 1420(w), 1488(w), 1920(s), 1950(s), 2021(s), 2036(m), 2856(w), 2926(w), 2961(w), 3134(w), 3849(w), 3951(w). Mp: 129 °C. 3b: 1H NMR (C6D6): δ 4.66 (2H), 4.41 (2H), 3.67 (4H) (ABCD, cp-H). 19F NMR (C6D6): δ 126.56 (d, 2J = 222 Hz, 2F); 128.55 (d, 2 J = 222 Hz, 2F); 168.29 (s, 1F). 13C{1H} NMR (C6D6): δ 223.06 (CO), 85.60, 84.74, 84.15, 82.00, 81.37. MS (EI): m/z (%) 568 (100) [M]þ and smaller fragments. HRMS (EI): calcd 567.89860, found 567.89720. IR (neat): 533(s), 562(w), 579(w), 627(s), 654(m), 668(m), 787(m), 804(m), (817(m), 827(m), 839(m), 844(m), 861(w), 913(m), 957(w), 984(w),1024(w), 1028(w), 1050(w), 1068(w), 1078(w), 1087(w), 1132(w), 1148(w), 1183(m), 1192(m), 1216(w), 1234(w), 1243(w), 1264(w), 1296(w), 1310(w), 1341(w), 1373(w), 1384(w), 1418(w), 1483(w), 1899(s), 1922(s), 1964(m), 2025(s), 3134(w), 3950(w). Mp: 105 °C. 4, 5: 153 mg (0.80 mmol) of cymantrene was dissolved in 20 mL of THF. Then 0.33 mL (0.83 mmol) of n-butyllithium (2.5 M in hexane) was added slowly under rapid stirring within one hour at 78 °C. Stirring was continued for one more hour before 200 mg (0.80 mmol) of 2 was added slowly during 20 min. Hydrolysis was performed by addition of 5 mL of aqueous sodium hydroxide solution (1 M). The solution was extracted with brine and ether. The organic phase was dried over magnesium sulfate. Column chromatographic purification on silica gel with pentane as eluent afforded 170 mg (0.38 mmol) of 4 in the fourth fraction (yield: 44%). Unreacted 2 was found in the first fraction, 2 with a fluorine-n-butyl exchange appeared in the second fraction, and unreacted cymantrene appeared in the third fraction. A fifth fraction yielded 80 mg (0.10 mmol) of 5 (yield: 13%). Dark red single crystals of both compounds were obtained by crystallization from dichloromethane at 4 °C. 4: 1H NMR (C6D6): δ 4.69, 4.52 (AA0 BB0 , 4 H, cp-H); 4.00 (s, 5H, cp-H); 3.96, 3.80 (AA0 BB0 , 4 H, cp-H). 19F NMR (C6D6): δ 145.66 (d, 3J = 121 Hz, 2F); 156.24 (d, 3J = 121 Hz, 2F). 13C{1H} NMR (C6D6): δ 223.74 (CO); 149.90 (dd, 2J(13C19F) = 49 Hz, 1J(13C19F) = 234 Hz), CF); 140.65 (dd, 2J(13C19F) = 51 Hz, 2065

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J(13C19F) = 229 Hz) CF); 90.45 (dd, 3J(13C19F) = 5 Hz, 2J(13C19F) = 29 Hz), ipso-C), 80.96, 80.09 (m), 72.06 (dd, 3J(13C19F) = 5 Hz, 2J(13C19F) = 27 Hz), ipso-C), 69.05, 68.97, 65.87 (m). MS (EI): m/z (%) 450 (37) [M]þ, 273 (100) [C14H11F2Fe]þ, and smaller fragments. HRMS (EI): calcd for C20H13F2O3FeMn 449.95627, found 449.95590; calcd for C20H13F2O3F54FeMn 447.96094, found 447.96075. IR (neat): 564(m), 571(s), 575(s), 593(m), 629(s), 644(w), 664(w), 684(w), 736(w), 799(m), 807(m), 817(m), 846(w), 862(w), 885(w), 901(w), 909(w), 937(w), 999(w), 1023(m), 1034(m), 1053(w), 1065(w), 1105(w), 1118(w), 1138(m), 1260(w), 1282(w), 1294(w), 1336(w), 1344(w), 1384(w), 1408(w), 1459(w), 1693(s), 1919(s), 2011(s). Anal. Calcd: C 53.37, H 2.91. Found: C 53.07, H 2.64. Mp: 135 °C. 5: 1H NMR (C6D6): δ 5.66 (s, 1H, cp-H); 4.74 (m, 2H, cp-H); 4.54, 3.98 (AA0 BB0 , 8H, cp-H); 4.02 (s, 10H, cp-H). 19F NMR (C6D6): δ 144.00 (d, 3J = 121 Hz, 2F); 156.95 (d, 3J = 121 Hz, 2F). MS (EI): m/z (%) 696 (66) [M]þ, 519 (100) [C26H19F4Fe2]þ, and smaller fragments. HRMS (EI): calcd 695.9507, found 695.9488. IR (neat): 528(m), 537(m), 555(w), 562(w), 572(w), 617(s), 626(s), 642(m), 661(m), 675(w), 675(m), 685(w), 720(w), 732(w), 760(w), 803(s), 816(s), 848(w), 863(w), 890(w), 947(w), 1000(m), 1026(m), 1066(m), 1081(w), 1104(m), 1134(s), 1200(w), 1214(w), 1257(w), 1283(w), 1292(w), 1334(w), 1351(w), 1363(w), 1391(w), 1411(w), 1451(w), 1460(w), 1688(w), 1904(m), 1924(s), 1947(s), 2022(s), 2853(w), 2924(w), 2962(w), 3113(w), 3128(w). Mp: 105 °C.

’ ASSOCIATED CONTENT

bS

Supporting Information. X-ray crystallographic data for 3a, 3b, 4, and 5. This material is available free of charge via the Internet at http://pubs.acs.org.

NOTE

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’ AUTHOR INFORMATION Corresponding Author

*Fax: þ49-30-838-53310. E-mail: [email protected].

’ ACKNOWLEDGMENT M.R. is indebted to the Hans-B€ockler-Foundation for a doctoral scholarship. Support from the Graduate School (GK 1582) “Fluorine as a Key Element” is gratefully acknowledged. ’ REFERENCES (1) Olsson, T.; Wennerstr€om, O. Acta Chem. Scand. 1978, B32, 293–296. (2) Gassman, P. G.; Winter, C. H. J. Am. Chem. Soc. 1986, 108, 4228–4229. (3) Akiyama, T.; Kato, K.; Kajitani, M.; Sakaguchi, Y.; Nakamura, J.; Hayashi, H.; Sugimori, A. G. Bull. Chem. Soc. Jpn. 1988, 61, 3531–3537. (4) Gassman, P. G.; Sowa, J. R.; Hill, M. G.; Mann, K. R. Organometallics 1995, 14, 4879–4885. (b) Gassman, P. G.; Mickelson, J. W.; Sowa, J. R. J. Am. Chem. Soc. 1992, 114, 6942–6944.  ermak, J.; Z adny , J.; Krupkova, A.; Lopatova, K.; Vlachova, (5) (a) C A.; Thi, T. H. N.; Sauliova, J.; Sy kora, J.; Císarova, I. J. Organomet. Chem.  ermak, J.; Krupkova, A.; Auerova, K.; 2007, 692, 1557–1570. (b) C Zamrzla, M.; Thi, T. H. N.; Vojtísek, P.; Císarova, I. J. Organomet. Chem.  ermak, J. 2010, 695, 375–381. (c) Bríza, T.; Kvícala, J.; Paleta, O.; C Tetrahedron 2002, 58, 3847–3854. (6) (a) Herrera, V.; De Rege, P. J. F.; Horvath, I. T.; Husebo, T. L.; Hughes, R. P. Inorg. Chem. Commun. 1998, 1, 197–199. (b) Hughes, R. P.; Trujillo, H. A. Organometallics 1996, 15, 286–294. (c) Hughes, R. P.; Husebo, T. L.; Rheingold, A. L.; Liable-Sands, L. M.; Yap, G. P. A. Organometallics 1997, 16, 5–7. (d) Hughes, R. P.; Maddock, S. M.; 2066

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