Well-Defined Butadienyl Organocopper(I ... - ACS Publications

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Well-Defined Butadienyl Organocopper(I) Aggregates from Zirconacyclopentadienes and CuCl: Synthesis and Structural Characterization Liang Liu, Weizhi Geng, Qi Yang, Wen-Xiong Zhang, and Zhenfeng Xi* Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, People’s Republic of China

Downloaded by UNIV OF NEBRASKA-LINCOLN on September 1, 2015 | http://pubs.acs.org Publication Date (Web): August 31, 2015 | doi: 10.1021/acs.organomet.5b00598

S Supporting Information *

ABSTRACT: Two examples of mixed alkenyl/aryl organocopper(I) aggregates possessing conjugated alkenyl/ aryl C−Cu bonds were synthesized by transmetalation of zirconaindenes with CuCl. Single-crystal X-ray structural analysis revealed tetrameric and hexameric structures. Butadienyl copper(I) aggregates were also synthesized and structurally characterized for further comparison. The preliminary reaction chemistry of the copper(I) aggregates was studied.

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1). When the monodentate tetrahydrothiophene (THT) ligand was used in the recrystallization step, a different black styrenyl

rganocopper(I) compounds play an important role in organometallic chemistry and are often proposed as key intermediates in Cu-promoted or -catalyzed organic synthesis.1,2 However, the isolation and characterization of organocopper(I) compounds remain a challenging issue, probably owing to their air and moisture sensitivity, thermal instability, and low solubility in common organic solvents.3−6 In contrast to alkynyl, aryl, and alkyl organocopper(I) compounds, well-defined alkenyl organocopper(I) compounds remain rare. Sadighi and Meyer reported the mononuclear and dinuclear alkenyl copper(I) complexes stabilized by Nheterocyclic carbene ligands, respectively.5e,f Spek reported the tetranuclear alkenyl copper(I) complexes with intramolecular coordination.5b Recently, we have reported the preparation of the octanuclear cis-butadienyl copper(I) trimer or tetramer from 1,4-dilithio-1,3-butadienes and CuCl.5h,7 There are only two examples of mixed alkenyl/aryl copper(I) compounds in the literature,5a,d in which the alkenyl and aryl moieties are separated. As far as we are aware, mixed alkenyl/ aryl organocopper(I) aggregates possessing conjugated alkenyl/ aryl C−Cu bonds have not been reported. Here we report the first successful synthesis, isolation, and characterization of two cis-styrenyl organocopper(I) aggregates by transmetalation of zirconaindenes with CuCl. Furthermore, two trimeric cisbutadienyl organocopper(I) complexes were isolated and characterized by a similar transmetalation procedure from zirconacyclopentadienes and CuCl. Zirconaindene 1 free of LiCl can be conveniently synthesized and isolated in high yields.8 Treatment of 1 with 3.0 equiv of CuCl in THF/TMEDA at −15 °C for 6 h afforded a brown solution. After the solvents were removed under reduced pressure at low temperature, the residue was recrystallized in Et2O/TMEDA at −20 °C to afford the styrenyl organocopper(I) aggregate 2 as black crystals in 53% isolated yield (Scheme © XXXX American Chemical Society

Scheme 1. Synthesis of Styrenyl Copper(I) Aggregates

copper(I) aggregate 3 free of halides could be generated and obtained in 27% isolated yield (Scheme 1). The structures of aggregates 2 and 3 were both determined by single-crystal Xray structural analysis. The X-ray structural analysis of the aggregate 2 revealed a tetrameric copper(I) complex containing 10 copper(I) atoms, 4 styrenyl skeletons, 2 anionic chlorides, and 2 neutral TMEDA ligands (Figure 1). A total of 10 copper(I) atoms form 2 Received: July 11, 2015

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DOI: 10.1021/acs.organomet.5b00598 Organometallics XXXX, XXX, XXX−XXX

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polynuclear alkenyl organocopper(I) compounds. In comparison to bidentate TMEDA in 2, THT has the advantages of softer property and less steric hindrance and thus can stabilize the copper(I) aggregates with a higher degree of aggregation. 1,2,3,4-Tetrasubstituted zirconacyclopentadienes such as 4a,b can be readily prepared and have been widely applied for the construction of C−C/C−X (X = Cl, Br, I) bonds and the synthesis of heterocycles or metalloles.10,11 Since these zirconacycles, with two alkenyl C−Zr bonds, are much different from zirconaindene 1, with one alkenyl C−Zr bond and one aryl C−Zr bond, we then treated these zirconacycles 4 with CuCl (Scheme 2), expecting organocopper(I) aggregates


Figure 1. Diamond drawing of 2 with 30% probability thermal ellipsoids. CH3 and CH2 moieties are omitted for clarity.

distorted tetrahedrons sharing one Cu5−Cu6 edge and 2 different butterfly-like quadrilaterals (Cu1, Cu2, Cu3, Cu4; Cu1′, Cu2′, Cu3′, Cu4′). The shorter Cu−Cu distances (2.3909(18)−2.8820(11) Å) indicates a stronger d10 Cu−Cu interaction,9 in comparison to that of previously reported complexes.5h The terminal alkenyl and aryl sp2 carbon atoms of styrenyl units are linked to four different copper(I) atoms via electron-deficient three-center−two-electron (3c-2e) bonds. The lengths of Calkenyl−Cu bonds (1.983(7)−2.010(7) Å) are comparable to those of Caryl−Cu bonds (1.982(7)−2.015(8) Å). Obviously, the tetrameric copper(I) aggregate 2 is significantly different from the previously reported butadienyl dicopper(I) tetramer,5h in which eight copper(I) atoms form a cubelike skeleton without the additional chlorides and TMEDA ligands. The X-ray structural analysis of the aggregate 3 revealed a hexameric structure compromising 12 copper(I) atoms, 6 styrenyl skeletons, and 2 THT ligands (Figure 2a). A total of 12

Scheme 2. Synthesis of Butadienyl Copper(I) Aggregates

different from 2 and 3. Thus, when pure tetrapropyl-substituted zirconacyclopentadiene 4a was treated with 3.4 equiv of CuCl in THF at −20 °C for 3 h, a yellow suspension was obtained. The yellow solid recrystallized in Et2O with 2.0 equiv of TMEDA at −20 °C to provide yellow crystals 5 in 72% isolated yield (Scheme 2). Similarly, treatment of the tetraethylsubstituted zirconacyclopentadiene 4b with 3.4 equiv of CuCl in THF at −15 °C for 10 min afforded complex 6 in 51% isolated yield. The aggregate 5 was relatively stable in Et2O below 10 °C but was highly sensitive to air and moisture. However, the aggregate 6 was more unstable than 5 and would thermally decompose in Et2O to give copper(I) mirror at 10 °C within 0.5 h. This observation indicates that the length of alkyl substituents on the butadienyl skeleton can significantly influence the thermal stability of their corresponding aggregates. The structures of aggregates 5 and 6 were both determined by single-crystal X-ray structural analysis. The aggregate 5 crystallized in the monoclinic P21/c space group; however, the aggregate 6 crystallized in the triclinic P1̅ space group. Aggregates 5 and 6 have almost the same configuration of copper(I) skeletons as well as bond lengths and angles. Therefore, only the structure of 5 is discussed here (Figure 3). The aggregate 5 comprises 10 copper(I) atoms, 3 butadienyl skeletons, 4 anionic chlorides, and 2 neutral TMEDA ligands. A

Figure 2. (a) Diamond drawing of 3 with 30% probability thermal ellipsoids. CH3 and CH2 moieties are omitted for clarity. (b) Coordination environments of styrenyl dicopper(I) units in 3.

copper atoms construct 8 distorted tetrahedrons. The Cu−Cu distances (2.4373(8)−3.0318(9) Å) suggest weaker d10 metal− metal interactions.9 The aggregate 3 contains three types of styrenyl copper(I) coordination environments, as shown in Figure 2b. In type I, the styrenyl moiety is linked to three copper(I) atoms, in type II, the styrenyl moiety is linked to a butterfly shape of four copper(I) atoms, and in type III, the styrenyl moiety is linked to three triangles sharing one vertex. It should be noted that two distinctive μ3-alkenyl carbon atoms (C17 and C17′) in type III are linked to three different copper(I) atoms. The three C17−Cu bond lengths are 2.019(4), 2.032(5), and 2.041(5) Å, respectively. Although the unusual μ3-bridged carbon atoms were observed in the polynuclear alkynyl copper(I) compounds,6 this aggregate 3 is the first example having μ3-bridged Csp2−Cu bonds in

Figure 3. Diamond drawing of 5 with 30% probability thermal ellipsoids. CH3 and CH2 moieties are omitted for clarity. B



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total of 10 copper(I) atoms form 5 distorted tetrahedrons and 2 triangles. There are 3 types of copper(I) atoms, with side copper(I) atoms coordinating with 2 bridging chlorides (Cu1, Cu10), 4 centered copper(I) atoms forming C−Cu−C bonds (Cu4, Cu5, Cu6, Cu7), and the other 4 forming C−Cu−Cl bonds (Cu2, Cu3, Cu8, Cu9). The short Cu−Cu distances (2.4076(12)−3.0410(13) Å) also indicate some weak d10 metal−metal interactions.9 The lengths of C−Cu bonds are in the range 1.979(7)−2.027(7) Å, while those of Cu−Cl bonds are in the range 2.163(2)−2.301(2) Å. 5 can be regarded as a variant of the previously reported trimeric butadienyl copper(I) aggregate by replacement of two lithium atoms with copper(I) atoms.5h The 13C NMR spectrum of 5 in d8-THF displayed six sets of peak signals for alkenyl carbon atoms, indicating that 5 did not dissociate into monomeric butadienyl dicopper(I) species even in polar solvents. The preliminary reactivity of organocopper(I) aggregates was investigated (Scheme 3). In the case of 5, its homocoupling in

THF afforded 7 in 89% isolated yield;5h,12 its reaction with 1,2diiodobenzene furnished the multiply substituted naphthalene 8 in 82% isolated yield.2b These results are very useful to understand the reaction mechanisms for the previously reported CuCl-mediated reactions of zirconacycles.11a,b,f−i In summary, we report the synthesis and structures of mixed alkenyl/aryl organocopper(I) aggregates. These results are fundamentally useful for understanding possible modes of organocopper(I) aggregates and CuCl-mediated reactions.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00598. Experimental details, X-ray data for 2, 3, 5, and 6, and scanned NMR spectra of all new products (PDF) X-ray data for 2, 3, 5, and 6 (CIF)

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REFERENCES

(1) For recent reviews on organocopper(I) chemistry, see: (a) van Koten, G.; Jastrezebski, J. T. B. H. Structural Organocopper Chemistry. In The Chemistry of Organocopper Compounds; Rappoport, Z., Marek, I., Eds.; Wiley-VCH: Weinheim, Germany, 2009; pp 23−143. (b) van Koten, G.; Pérez, P. J.; Liebeskind, L. S. Organometallics 2012, 31, 7631−7633. (c) Yoshikai, N.; Nakamura, E. Chem. Rev. 2012, 112, 2339−2372. (2) For proposed organocopper(I) intermediates, see: (a) Yoshifuji, M.; Loots, M. J.; Schwartz, J. Tetrahedron Lett. 1977, 18, 1303−1306. (b) Takahashi, T.; Hara, R.; Nishihara, Y.; Kotora, M. J. Am. Chem. Soc. 1996, 118, 5154−5155. (c) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. Angew. Chem., Int. Ed. 2002, 41, 2596−2599. (d) Li, G.; Fang, H.; Zhang, S.; Xi, Z. Tetrahedron Lett. 2004, 45, 8399−8402. (e) Wang, C.; Yuan, J.; Li, G.; Wang, Z.; Zhang, S.; Xi, Z. J. Am. Chem. Soc. 2006, 128, 4564−4565. (f) Luo, Q.; Wang, C.; Zhang, W.-X.; Xi, Z. Chem. Commun. 2008, 1593−1595. (g) Thapa, S.; Basnet, P.; Gurng, S. K.; Giri, R. Chem. Commun. 2015, 51, 4009− 4012. (h) Shi, S.-L.; Buchwald, S. L. Nat. Chem. 2015, 7, 38−44. (3) For alkyl organocopper(I) compounds, see: (a) Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973, 24−25. (b) Panferova, L. I.; Miloserdov, F. M.; Lishchynskyi, A.; Belmonte, M. M.; BenetBuchholz, J.; Grushin, V. V. Angew. Chem., Int. Ed. 2015, 54, 5218− 5222. (4) For aryl organocopper(I) compounds, see: (a) Cairncross, A.; Omura, H.; Sheppard, W. A. J. Am. Chem. Soc. 1971, 93, 248−249. (b) He, X.; Ruhlandt-Senge, K.; Power, P. P.; Bertz, S. H. J. Am. Chem. Soc. 1994, 116, 6963−6964. (c) Eriksson, H.; Håkansson, M. Organometallics 1997, 16, 4243−4244. (d) Nolte, C.; Mayer, P.; Straub, B. F. Angew. Chem., Int. Ed. 2007, 46, 2101−2103. (5) For alkenyl organocopper(I) compounds, see: (a) Noltes, J. G.; ten Hoedt, R. W. M.; van Koten, G.; Spek, A. L.; Schoone, J. C. J. Organomet. Chem. 1982, 225, 365−376. (b) Smeets, W. J. J.; Spek, A. L. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1987, 43, 870−873. (c) Janssen, M. D.; Köhler, K.; Herres, M.; Dedieu, A.; Smeets, W. J. J.; Spek, A. L.; Grove, D. M.; Lang, H.; van Koten, G. J. Am. Chem. Soc. 1996, 118, 4817−4829. (d) Schulte, P.; Behrens, U.; Olbrich, F. Z. Anorg. Allg. Chem. 2000, 626, 1692−1696. (e) Hu, X.; CastroRodriguez, I.; Meyer, K. Organometallics 2003, 22, 3016−3018. (f) Mankad, N. P.; Laitar, D. S.; Sadighi, J. P. Organometallics 2004, 23, 3369−3371. (g) Bruce, M. I.; Zaitseva, N. N.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2008, 693, 1400−1404. (h) Geng, W.; Wei, J.; Zhang, W.-X.; Xi, Z. J. Am. Chem. Soc. 2014, 136, 610− 613. (6) For alkynyl organocopper(I) compounds, see: (a) Osakada, K.; Takizawa, T.; Yamamoto, T. Organometallics 1995, 14, 3531−3538. (b) Lang, H.; Jakob, A.; Milde, B. Organometallics 2012, 31, 7661− 7693. (7) Xi, Z. Acc. Chem. Res. 2010, 43, 1342−1351. (8) Buchwald, S. L.; Watson, B. T.; Huffman, J. C. J. Am. Chem. Soc. 1986, 108, 7411−7413. (9) For d10 Cu−Cu interaction, see: Yam, V. W.-W.; Lo, K. K.-W. Chem. Soc. Rev. 1999, 28, 323−334. (10) Negishi, E.; Cederbaum, F. E.; Takahashi, T. Tetrahedron Lett. 1986, 27, 2829−2832. (11) For synthesis and applications of zirconacyclopentadienes, see: (a) Takahashi, T.; Kotora, M.; Xi, Z. J. Chem. Soc., Chem. Commun. 1995, 361−362. (b) Takahashi, T.; Xi, Z.; Yamazaki, A.; Liu, Y.; Nakajima, K.; Kotora, M. J. Am. Chem. Soc. 1998, 120, 1672−1680. (c) Ura, Y.; Li, Y.; Xi, Z.; Takahashi, T. Tetrahedron Lett. 1998, 39, 2787−2790. (d) Takahashi, T.; Li, Y. Zirconacyclopentadienes in Organic Synthesis. In Titannium and Zirconium in Organic Synthesis; Marek, I., Ed.; Wiley-VCH: Weinheim, Germany, 2002; pp 50−85. (e) Dufková, L.; Kotora, M.; Císařová, I. Eur. J. Org. Chem. 2005, 2005, 2491−2499. (f) Chen, C.; Xi, C.; Jiang, Y.; Hong, X. J. Am. Chem. Soc. 2005, 127, 8024−8025. (g) Chen, C.; Xi, C.; Ai, Z.; Hong, X. Org. Lett. 2006, 8, 4055−4058. (h) Song, Z.; Li, Y.; Liu, M.; Cong, L.; Liu, Y. Organometallics 2006, 25, 5035−5044. (i) Zhou, Y.; Yan, X.; Chen, C.;

Scheme 3. Reaction of Organocopper(I) Aggregate 5

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Corresponding Author

*E-mail for Z.X.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the 973 Program (2011CB808700) and the Natural Science Foundation of China (NSFC). Dedicated to Professor Todd B. Marder on the occasion of his 60th birthday. C


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Xi, C. Organometallics 2013, 32, 6182−6185. (j) Yan, X.; Xi, C. Acc. Chem. Res. 2015, 48, 935−946. (12) Ubayama, H.; Sun, W.-H.; Xi, Z.; Takahashi, T. Chem. Commun. 1998, 1931−1932.

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Well-Defined Butadienyl Organocopper(I ... - ACS Publications

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