Communication pubs.acs.org/Organometallics
Rotaxanes Derived from Dimetallic Polyynediyl Complexes: Extended Axles and Expanded Macrocycles Zuzana Baranová, Hashem Amini, Nattamai Bhuvanesh, and John A. Gladysz* Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012, United States S Supporting Information *
ABSTRACT: A new 35-membered macrocycle 3b derived from 1,10phenanthroline and two 2,9-p-C6H4O(CH2)6O substituents that tether a 2,7-naphthdiyl moiety is synthesized. CuI complexes of 3b and a previously reported analog in which the naphthdiyl is replaced by a m-C6H4 group (3a) are reacted with the hexatriynyl complex trans-(C6F5)(p-tol3P)2Pt(CC)3H (1.0:2.5 mol ratios) in the presence of K2CO3 (4.0−5.0 equiv) and I2 (1.3−1.8 equiv) in THF at 55 °C. Workups afford the rotaxanes 5·3a and 5·3b (45− 23%), in which the macrocycles are threaded by the sp carbon chain of the diplatinum dodecahexaynediyl complex trans,trans-(C6F5)(p-tol3P)2Pt(C C)6Pt(Pp-tol3)2(C6F5) (5), which is also obtained as a byproduct. The yields of 5·3a and 5·3b are much higher than in the case with octatetraynediyl (C8) analogs, and their spectroscopic properties and crystal structures are analyzed in detail, especially with reference to recent DFT studies.
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follow-up study with Halet, the nature of the mechanical bond and other properties were probed computationally.12 However, the yields of 2·3a were low (ca. 9%). We wondered whether accessibilities would improve with longer sp chains and/or expanded macrocycles. Longer terminal polyynes undergo more facile oxidations3,4 and afford sterically less congested systems, allowing more flexibility in macrocycle positioning. In important related work, rotaxanes based upon longer organic polyynes (C8, C12, C20) have been similarly prepared by Tykwinski and Anderson.13,14 The copper iodide macrocycle complex utilized earlier, (3a)CuI, was employed for this study,6,11 together with a homologue (3b)CuI in which the m-C6H4 group was replaced by a sterically expanded 2,7-naphthdiyl moiety. The latter represents a new compound, and full preparative details, which parallel those published for (3a)CuI,11 are provided in the Supporting Information. The platinum hexatriynyl complex trans-(C6F5)(p-tol3P)2Pt(CC)3H (4) was isolated as previously described.4a As shown in Scheme 2, it was combined with (3a)CuI or (3b)CuI (2.5:1.0 mol ratio) and K2CO3 (4.0−5.0 equiv) in THF at 55 °C in the presence of I2 (1.3−1.8 equiv). Chromatographic workups gave some of the previously characterized dodecahexaynediyl complex trans,trans-(C6F5)(p-tol3P)2Pt(CC)6Pt(Pp-tol3)2(C6F5) (5; 30% based upon 4 in the reaction with (3a)CuI).4a However, the major products corresponded to the target rotaxanes 5·3a (45% based upon limiting macrocycle) and 5·3b (28−23%). These yields are much higher than those
here is now extensive literature involving assemblies in which two redox active metal fragments1−6 or break junctions7 are bridged by wire-like unsaturated moieties. A variety of electron transport phenomena involving the two termini have been investigated. One aspect that remains poorly explored is the effect of “insulation” about the linkers, a feature essential for many practical applications of macroscopic wires. For example, shielded environments could have a substantial influence upon electron delocalization8 and reorganization energies9 in paramagnetic “mixed valence” compounds. For some time, we have been interested in dimetallic polyynediyl complexes of the formula LmM(CC)nMLm.3,4 These feature unsaturated linkers that can never be rotated “out of conjugation”, as would be possible with poly(p-phenylene) systems and have attracted attention in many other laboratories as well.2 We have explored several strategies for sterically shielding the sp carbon chains in these assemblies, as generalized by structure I in Scheme 1.5,6 Our earliest efforts involved covalently attached sp3 carbon chains, per the double helical species II.5 A workhorse reaction throughout all of this chemistry is the oxidative homocoupling of terminal polyynyl complexes, such as the platinum butadiynyl complex trans-(C6F5)(p-tol3P)2Pt(CC)2H (1), with various copper based recipes to the corresponding polyynediyl species, such as the diplatinum octatetraynediyl complex trans,trans-(C6F5)(p-tol3P)2Pt(C C)4Pt(Pp-tol3)2(C6F5) (2). Employing an “active template” strategy10 used by Saito with organic terminal monoynes,11 we recently reported that the reaction of 1 with the 1,10phenanthroline/m-C 6H4 anchored copper(I) macrocycle (3a)CuI (see Scheme 2) in the presence of a suitable oxidant afforded the rotaxane 2·3a (Scheme 1), an insulated molecular wire that unlike II is based upon noncovalent interactions. In a © XXXX American Chemical Society
Received: October 7, 2014
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Scheme 1. General Representation of an “Insulated” Dimetallic Polyynediyl Complex (I), and Prior Art (II, 2·3a)
Scheme 2. Rotaxanes Derived from Diplatinum Dodecahexaynediyl Complex 5
Figure 1. 1H NMR spectra of new rotaxanes as compared to their axle and macrocycle components.
differences in the CH2 signals were less than 1.0 ppm. The ptol3P methyl 1H signals also moved upfield (Δ 0.11−0.14 ppm), which was ascribed to shielding by the arene moieties of the macrocycles. However, as with most other resonances mentioned above, the magnitude of the shift was less than that with 2·3a (Δ 0.24 ppm). The 31P NMR spectrum of 5 was essentially unaffected upon rotaxane formation. In accord with TD-DFT calculations,12 the UV−visible spectra were nearly the sum of those of 5 and 3a,b, without any new absorptions indicative of electronic interactions. The IR spectra of 5·3a and 5·3b showed ν(C C) bands with frequencies similar to those of 5 (powder film, cm−1: 5·3a 2160/2090/1993; 5·3b 2127/2088/1992; 5 2131/ 2092/2015 cm−1). In the case of 5·3b, a mass spectrum exhibited a strong molecular ion (MALDI+, m/z 2774, 5·3b + H, 45%). Solvates of both rotaxanes could be crystallized, and X-ray structures were obtained as described in the Supporting Information. Thermal ellipsoid and space filling representations
realized for 2·3a, presumably due to the steric and/or electronic reasons noted above. The rotaxane structures were evidenced by a variety of data, such as the 1H NMR spectra in Figure 1. The OCH2CH2CH2 signals shifted upfield from those of the macrocycles (Δ 0.32− 0.41 ppm), as seen with the lower homologue 2·3a (Δ 0.65− 0.82 ppm) and in accord with the magnetic shielding anisotropy of conjugated polyynes.15 The proton between the two m-C6H4 substituents in 5·3a also shifted upfield (Δ 0.24 ppm), as did the peri 1,8-naphthyl protons between the 2,7 substituents in 5·3b (Δ >0.15 ppm, overlapping). In the 13C NMR spectrum, the carbon atom between the two m-C6H4 substituents in 5·3a exhibited an upfield shift (Δ 2.4 ppm), but B
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Figure 2. Thermal ellipsoid plots (50% probability levels) and space filling representations of the molecular structures of 5·3a (left) and 5·3b (right).
the same time, the macrocycle geometries vary from those found in 2·3a (C8, C10) to tilted and interacting with both end groups (C12) to perpendicular and abutting one end group (C14). Of course, these gas phase calculations do not take into account lattice packing forces that influence the results in Figure 2. However, the degree to which the limiting geometries are delineated is impressive. A number of other structural features can be compared (Supporting Information),17 and these will be more fully analyzed in our full paper. Electrochemical oxidations of 5·3a and 5·3b, and the lower homologue 2·3a, are complicated by the fact that the macrocycles 3a,b are, in accord with their extensive unsaturation, independently electroactive. They undergo irreversible oxidations at potentials comparable to those at which the axle 5 undergoes partially reversible oxidation.4a,6 Accordingly, the cyclic voltammograms of 5·3a and 5·3b are, with the exception of a gradually increasing anodic current, featureless. Thus, while the sp chains in these assemblies can be viewed as sterically insulated, the macrocycles provide loci for new redox chemistry that would have no counterpart in saturated systems such as II (Scheme 1). Thus, one future challenge will be to engineer rotaxanes based upon saturated macrocycles that feature as few heteroatoms as possible, and/or in which trivalent nitrogen atoms are derivatized in a postsynthetic modification. The viability of nitrogen donor atom chemistry has been demonstrated by Tykwinski and Anderson, who complexed the 1,10-phenanthroline moiety of a rotaxane derived from 3a and an organic dodecahexayne to Re(CO)3Cl.13 In summary, this investigation has (1) established that rotaxanes derived from dimetallic polyynediyl complexes can be
are given in Figure 2. Although the PtC12Pt linkages exhibit slightly different conformations (bow- and S-shaped),16 the bond lengths do not significantly differ from those of the free axle 5 (Table S2, Supporting Information).4a Unlike the lower homologue 2·3a, the macrocycles are no longer firmly wedged between the p-tol3P moieties of the end groups. In all three systems, the aromatic rings remain remote from the sp carbon chains (shortest oxygen atom−Csp and nitrogen atom−Csp distances, 4.722−4.483 Å and 7.105−7.729 Å). None of the hydrogen atoms associated with sp2 carbon atoms of the macrocycle are within van der Waals contact with the sp chain, but some associated with sp3 carbon atoms are.17 The average Csp−Csp3 distances in 5·3a and 5·3b (4.603 Å, 4.350 Å) are somewhat greater than that in 2·3a (4.242 Å), consistent with NMR shielding trends noted above. In 5·3a, the macrocycle is approximately perpendicular to the axle and abuts one end group. In contrast, the macrocycle in 5· 3b tilts so as to realize van der Waals contacts with both end groups. These features are of interest in the context of computational studies carried out on 2·3a, 5·3a, and analogs of varying sp chain lengths.12 The noncovalent axle/macrocycle binding energies were found to derive from not only van der Waals interactions enforced by the close proximities of the sp carbon chains and macrocycles but also the weak hydrogen bonding between the p-tol3P protons and nitrogen and oxygen atoms of the macrocycles. Close inspection of the crystal structures also suggests attractive C−H/π interactions. The total computed binding energies drop from 13.27 kcal/mol for 2·3a (C8) to 11.41 kcal/mol for the corresponding decapentaynediyl (C10) adduct to a plateau of 7.71−8.15 kcal/mol for 5·3a (C12) and the tetradecaheptaynediyl (C14) adduct.12 At C
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Frisch, A. C.; Hampel, F.; Gladysz, J. A. Chem.Eur. J. 2006, 12, 6486−6505. (5) (a) Stahl, J.; Mohr, W.; de Quadras, L.; Peters, T. B.; Bohling, J. C.; Martín-Alvarez, J. M.; Owen, G. R.; Hampel, F.; Gladysz, J. A. J. Am. Chem. Soc. 2007, 129, 8282−8295. (b) de Quadras, L.; Bauer, E. B.; Mohr, W.; Bohling, J. C.; Peters, T. B.; Martín-Alvarez, J. M.; Hampel, F.; Gladysz, J. A. J. Am. Chem. Soc. 2007, 129, 8296−8309. (c) de Quadras, L.; Bauer, E. B.; Stahl, J.; Zhuravlev, F.; Hampel, F.; Gladysz, J. A. New J. Chem. 2007, 31, 1594−1604. (d) Owen, G. R.; Stahl, J.; Hampel, F.; Gladysz, J. A. Chem.Eur. J. 2008, 14, 73−87. (6) Weisbach, N.; Baranová, Z.; Gauthier, S.; Reibenspies, J. H.; Gladysz, J. A. Chem. Commun. 2012, 48, 7562−7564. (7) (a) Meisner, J. S.; Kamenetska, M.; Krikorian, M.; Steigerwald, M. L.; Venkataraman, L.; Nuckolls, C. Nano Lett. 2011, 11, 1575− 1579. (b) Aradhya, S. V.; Venkataraman, L. Nat. Nanotechnol. 2013, 8, 399−410. (c) Song, H.; Reed, M. A.; Lee, T. Adv. Mater. 2011, 23, 1583−1608. (d) Haick, H.; Cahen, D. Prog. Surf. Sci. 2008, 83, 217− 261. (e) Huang, C.; Yang, J. Nano-Micro Lett. 2011, 3, 1−5. (f) Zhou, X.-Y.; Peng, Z.-L.; Sun, Y.-Y.; Wang, L.-N.; Niu, Z.-J.; Zhou, X.-S. Nanotechnology 2013, 24, 465204. (g) Zhou, X.-Y.; Wang, Y.-H.; Qi, H.-M.; Zheng, J.-F.; Niu, Z.-J.; Zhou, X.-S. Nanoscale Res. Lett. 2014, 9, 77. (h) Xing, Y.; Park, T.-H.; Venkatramani, R.; Keinan, S.; Beratan, D. N.; Therien, M. J.; Borguet, E. J. Am. Chem. Soc. 2010, 132, 7946− 7956. (i) Moreno-García, P.; Gulcur, M.; Manrique, D. Z.; Pope, T.; Hong, W.; Kaliginedi, V.; Huang, C.; Batsanov, A. S.; Bryce, M. R.; Lambert, C.; Wandlowski, T. J. Am. Chem. Soc. 2013, 135, 12228− 12240. (8) Demadis, K. D.; Hartshorn, C. M.; Meyer, T. J. Chem. Rev. 2001, 101, 2655−2685. (9) (a) Myers, A. B. Chem. Rev. 1996, 96, 911−926. (b) Sutin, N. Prog. Inorg. Chem. 2009, 30, 441. (c) Ghosh, S.; Horvath, S.; Soudackov, A. V.; Hammes-Schiffer, S. J. Chem. Theory Comput. 2014, 10, 2091−2102. (10) Crowley, J. D.; Goldup, S. M.; Lee, A.-L.; Leigh, D. A.; McBurney, R. T. Chem. Soc. Rev. 2009, 38, 1530−1541. (11) (a) Saito, S.; Takahashi, E.; Nakazono, K. Org. Lett. 2006, 8, 5133−5136. (b) Sato, Y.; Yamasaki, R.; Saito, S. Angew. Chem., Int. Ed. 2009, 48, 504−507; Angew. Chem. 2009, 121, 512−515. (12) Sahnoune, H.; Baranová, Z.; Bhuvanesh, N.; Gladysz, J. A.; Halet, J.-F. Organometallics 2013, 32, 6360−6367. (13) Movsisyan, L. D.; Kondratuk, D. V.; Franz, M.; Thompson, A. L.; Tykwinski, R. R.; Anderson, H. L. Org. Lett. 2012, 14, 3424−3426. (14) For partially characterized rotaxanes derived from organic dodecahexaynes (C12) and cyclodextrins, see: Sugiyama, J.; Tomita, I. Eur. J. Org. Chem. 2007, 4651−4653. (15) Wannere, C. S.; Schleyer, P. v. R. Org. Lett. 2003, 5, 605−608. (16) (a) Szafert, S.; Gladysz, J. A. Chem. Rev. 2003, 103, 4175−4206. (b) Szafert, S.; Gladysz, J. A. Chem. Rev. 2006, 106, PR1−PR33. (17) Some close contacts are as follows (atom labels from CIF files in Supporting Information). (a) Macrocycle hydrogen atom/Csp: 5·3a, H36B(Csp3)···C7(Csp) 2.909 Å;18 H17M(Csp2)···C3(Csp) 3.281 Å; 5· 3b, H24A(Csp3)···C9(Csp) 2.873 Å;18 H30M(Csp2)···C8(Csp) 3.034 Å. (b) Macrocycle heteroatom/p-tol3P hydrogen atom: 5·3a, N1M··· H25C(Csp3) 3.245 Å (others longer); 5·3b, O3M···H41C(Csp2) 2.644 Å;18 O2M···H73C(Csp3) 2.888 Å;18 N2M···H10F(Csp3) 3.398 Å. (c) Macrocycle carbon atom/p-tol3P hydrogen atom: 5·3a, C15M(Csp2)··· H53A(Csp3), 2.827 Å;18 5·3b, C16M(Csp2)···H104(Csp2) 2.760 Å.18 (18) These values are less than or equal to the sums of the van der Waals radii: Bondi, A. J. Phys. Chem. 1964, 68, 441−451.
accessed in greatly improved yields when the axle is extended beyond eight sp carbons, (2) expanded the range and ring sizes of macrocycles that can be employed, and (3) defined a variety of structural and spectroscopic properties that provide valuable baselines for subsequent studies. The macrocycle positions and conformations can be rationalized computationally and reflect weak hydrogen bonding and other interactions with the end groups. Attempts are currently being made to further extend the sp chains, introduce bulkier (or multiple) macrocycles to achieve greater degrees of steric insulation, and design redox resistant macrocycles that can be applied in Scheme 2.
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ASSOCIATED CONTENT
S Supporting Information *
Text and tables giving experimental procedures and spectroscopic and crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We thank the U.S. National Science Foundation (CHE1153085) for support, Dr. Howard Williams and Ms. Vanessa Santiago for measurements, and Mr. Joseph S. Villalpando and Mr. Alex Kalin for syntheses of precursors. Crystallographic data were collected through the RAPIDD (Rapid Access Proposals, Industry, and Director’s Discretion) program at the Small-Crystal Crystallography Beamline 11.3.1 at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory. The ALS is supported by the Director, Office of Sciences, Office of Basic Energy Sciences, of the U.S. Department of Energy, under Contract DE-AC02-05CH11231.
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REFERENCES
(1) Some lead reviews from an extensive literature: (a) Barlow, S.; O’Hare, D. Chem. Rev. 1997, 97, 637−669. (b) Astruc, D. Acc. Chem. Res. 1997, 30, 383−391. (c) Paul, F.; Lapinte, C. Coord. Chem. Rev. 1998, 178−180, 431−509. (d) McCleverty, J. A.; Ward, M. D. Acc. Chem. Res. 1998, 31, 842−851. (e) Akita, M.; Sakurai, A.; Chung, M.C.; Moro-oka, Y. J. Organomet. Chem. 2003, 670, 2−10. (f) AguirreEtcheverry, P.; O’Hare, D. Chem. Rev. 2010, 110, 4839−4864. (g) Low, P. J. Coord. Chem. Rev. 2013, 257, 1507−1532. (h) Halet, J.-F.; Lapinte, C. Coord. Chem. Rev. 2013, 257, 1584−1613. (2) Representative papers since 2012 from other research groups active with polyynediyl complexes: (a) Fitzgerald, E. C.; Brown, N. J.; Edge, R.; Helliwell, M.; Roberts, H. N.; Tuna, F.; Beeby, A.; Collison, D.; Low, P. J.; Whiteley, M. W. Organometallics 2012, 31, 157−169. (b) Egler-Lucas, C.; Blacque, O.; Venkatesan, K.; López-Hernández, A.; Berke, H. Eur. J. Inorg. Chem. 2012, 1536−1545. (c) Lissel, F.; Fox, T.; Blacque, O.; Polit, W.; Winter, R.; Venkatesan, K.; Berke, H. J. Am. Chem. Soc. 2013, 135, 4051−4060. (d) Cao, Z.; Xi, B.; Jodoin, D. S.; Zhang, L.; Cummings, S. P.; Gao, Y.; Tyler, S. F.; Fanwick, P. E.; Crutchley, R. J.; Ren, T. J. Am. Chem. Soc. 2014, 136, 12174−12183. (e) Burgun, A.; Gendron, F.; Sumby, C. J.; Roisnel, T.; Cador, O.; Costuas, K.; Halet, J.-F.; Bruce, M. I.; Lapinte, C. Organometallics 2014, 33, 2613−2627. (f) Cook, T. D.; Fanwick, P. E.; Ren, T. Organometallics 2014, 33, 4621−4624. (3) Dembinski, R.; Bartik, T.; Bartik, B.; Jaeger, M.; Gladysz, J. A. J. Am. Chem. Soc. 2000, 122, 810−822. (4) (a) Mohr, W.; Stahl, J.; Hampel, F.; Gladysz, J. A. Chem.Eur. J. 2003, 9, 3324−3340. (b) Zheng, Q.; Bohling, J. C.; Peters, T. B.; D
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