Communication Cite This: Organometallics XXXX, XXX, XXX−XXX
Constitutional Isomers of Macrocyclic Tetraruthenium Complexes with Vastly Different Spectroscopic and Electrochemical Properties Daniel Fink, Michael Linseis, and Rainer F. Winter* Fachbereich Chemie, Universität Konstanz, 78457 Konstanz, Germany S Supporting Information *
ABSTRACT: Two constitutionally isomeric tetraruthenium macrocycles were constructed from either symmetrically (2-S) or unsymmetrically (2-A) functionalized thiophene-based building blocks. Both compounds were fully characterized by NMR spectroscopy and high-resolution ESI MS. Despite their identical composition and close structural resemblance, the two isomers exhibit vastly different electrochemical and spectroscopic properties as a consequence of the different extensions of their π-conjugated subunits. In particular, mixedvalent 2-A+/2+/3+ absorb weakly in the near infrared as a consequence of electronic through-bond coupling between neighboring oxidized and reduced sites, whereas 2-S+/2+/3+ do not.
sort of self-complementary thiophene linker. While similar in shape and size, they strongly differ in their electrochemical behavior and the spectroscopic properties of their oxidized forms. The two isomeric tetraruthenium macrocycles of Scheme 1 were obtained from either symmetrically (2-S) or unsymmetri-
Metallamacrocycles are generally constructed from metal ions and appropriately substituted bifunctional organic bridging ligands (so-called linkers). Early work of Verkade1 sparked enormous work in this field, which meanwhile led to a plethora of macrocyclic structures with varied nuclearities and shapes.2 Apart from their appealing beauty, such structures have meanwhile found use in sensing applications,3 as selective hosts for appropriate guest molecules,4 or as miniaturized reaction vessels for chemical reactions in confined environments.5 Although most metallamacrocycles feature redox-active metal−coligand entities, linkers, or both, their electrochemical properties have remained rather little explored or have mostly been studied at a merely qualitative level.6 Important exceptions come from the intriguing work of Hupp, Kaim, Stang, Therrien, and their coworkers7,8 and the elegant work of Mayor and Long on rigid, πconjugated organometallic macrocycles with ferrocene- or biferrocene-centered oxidations.9 Remarkable recent developments are the redox-driven disassembly/reassembly of neutral or cationic tetrapalladium metallamacrocycles10,11 and the reversible release and uptake of a coronene guest molecule on oxidation/reduction of a neutral tetraplatinum congener10 as well as the use of dipyridylbenzene-bridged triruthenium macrocycles as highly efficient and robust water oxidation catalysts.12 We have recently reported on redox-active tri- and tetraruthenium macrocycles built by self-assembly of an ethynylarylcarboxylate linker with a hydride ruthenium precursor or from divinylphenylene-bridged diruthenium and isophthalate synthons.13−15 The tetraruthenium complexes feature two conjugated but mutually insulated Ru−CHCH−C6H4− CHCH−Ru entities,13,14 whereas the triruthenium complexes showed intramolecular intercomponent charge transfer in their one- and two-electron-oxidized, mixed-valent (MV) states.15 Following these two alternative construction principles, we have now prepared two constitutional isomers of tetraruthenium macrocycles from either two different building blocks or just one © XXXX American Chemical Society
Scheme 1. Isomeric Macrocycles 2-A and 2-S
cally (2-A) 2,5-disubstituted thiophene linkers. The C4symmetric macrocycle 2-A was obtained in 52% isolated yield by reacting the hydride complex HRu(CO)Cl(PiPr3)2 with equimolar amounts of 5-ethynylthiophene-2-carboxylic acid in the presence of K2CO3. Isomeric macrocycle 2-S with (idealized) Received: January 29, 2018
A
DOI: 10.1021/acs.organomet.8b00057 Organometallics XXXX, XXX, XXX−XXX
Communication
Organometallics
only the first wave/square wave peak is resolved with some larger splitting of 98 mV for 2-A in comparison to 70 mV for 2-S (Table 1). Using the NBu4BArF supporting electrolyte with the very
C2v symmetry was obtained in 70% yield by combining thiophene-2,5-dicarboxylate with the divinylthiophene-bridged diruthenium complex {Ru(CO)Cl(P iPr3)2}2(μ-2,5-(CH CH)2 -C 4H2 S) (1-S) (see Figure S1 in the Supporting Information).16 Due to their inherently high symmetry, both macrocycles show just one sharp 31P{1H} singlet NMR resonance at δ 38.13 (2-S) or 39.56 ppm (2-A, see Figures S2 and S3 in the Supporting Information). The characteristic signals for the vinyl protons in the 1H NMR spectrum are located at δ 8.79 and 6.80 ppm (2-S) or at δ 9.67 and 6.88 ppm (2-A), respectively. In agreement with the proposed structures, the thiophene protons of 2-A give rise to two different resonance signals, integrating as 4 H each, with a characteristic coupling constant of 3.7 Hz. In contrast, they appear as two singlet resonances (4 H each) in 2-S. Other proton resonances as well as the signals in the 13C{1H} NMR spectra also agree with the expectations (see Figures S4− S7 in the Supporting Information). High-resolution ESI MS studies confirmed that 2-S and 2-A are constitutional isomers of tetraruthenium macrocycles by virtue of their nearly identical molecule ion peaks at m/z 2407.6708 for 2-S or at 2407.6754 for 2-A (calcd 2407.6798) with the expected isotope patterns (see Figures S8−S13 in the Supporting Information). In addition, we were able to grow single crystals of the benzene trisolvate of macrocycle 2-S that lent themselves for X-ray crystallography. Details of the data collection, refinement, and bond parameters can be found in Tables S1−S3 in the Supporting Information. The molecular structure is shown in Figure 1 and Figure S14 in the Supporting Information.
Table 1. Half-Wave Potentials (mV) of Macrocycles 2-S and 2A and the Dinuclear Precursor Complex 1-S in mV vs Cp2Fe0/+ a 1-S 2-A 2-S a
E1/20/+
E1/2+/2+
E1/22+/3+
E1/23+/4+
−294 (−360) 25 (−36) −452 (−547)
36 (−10) 123 (59) −382 (−477)
347 (344) −43 (−91)
347 (468) −43 (−14)
In CH2Cl2/nBu4NPF6 (in CH2Cl2/nBu4NBArF).
weakly ion pairing B{C6H3(CF3)2-3,5}4− counterion splits the first two waves by a larger amount and also resolves the second oxidation into individual one-electron steps (Table 1 and Tables S4 and S5 and Figures S15−S21 in the Supporting Information). A comparison of macrocyle 2-S with its diruthenium precursor 1-S reveals a cathodic shift of ca. 150 mV for the first oxidation wave. This is the expected consequence of increasing the valence electron count at the Ru centers from 16 to 18 on substitution of a chloro by a carboxylato ligand.13,14 Most remarkably, the halfwave potentials of 2-S are 505−380 mV lower than those of the equivalent redox processes in 2-A. This indicates a significantly higher ability of the more extended, π-conjugated divinylthiophene diruthenium entities to accommodate positive charge(s) in comparison to a monoruthenium vinylthiophene carboxylate unit. In their neutral states, isomers 2-S and 2-A exhibit nearly identical energies of the Ru(CO) stretching vibration ν(CO) and their electronic transitions. Differences in their electronic properties become, however, manifest in their oxidized forms, as revealed by IR and UV/vis/NIR spectroelectrochemistry. The results for 2-S closely resemble those of previously characterized 2 + 2 macrocycles built from π-conjugated divinylarylenebridged diruthenium building blocks and isophthalate linkers13,14 or its precursor 1-S.16 On 1e− oxidation of every divinylaryleneRu2 side, the Ru(CO) band shifts to 30 cm−1 higher energy, while in the visible (vis) and the near-infrared (NIR) intense, structured bands with main peaks at 648 and 1051 nm develop (see Figures S22−S24 and Table S6 in the Supporting Information). This indicates delocalization of the positive charge over the entire {Ru}−CHCH−C4H2S−CHCH−{Ru} array ({Ru} = Ru(CO)(PiPr3)2). The absence of any low-energy absorption band specific for the intermittently formed oneelectron-oxidized radical cation with one oxidized and one reduced side indicates the absence of any detectable throughbond or through-space electronic interactions between the conjugated sides. Hence, the redox splitting ΔE1/2 between the 2S0/+ and the 2-S+/2+ waves is entirely due to electrostatic effects. Further oxidation to tetracation 2-S4+ shifts ν(CO) and the prominent visible band blue to 1976 cm−1 or to 603 nm while it collapses the NIR band of the open-shell {Ru}−CHCH− C4H2S−CHCH−{Ru}•+ chromophores. Again, the spectroscopic fingerprints of 2-S4+ are nearly identical with those of 1S2+ with a rough doubling of molar extinction coefficients ε due to the presence of two chromophoric units within the same molecule. 2-A, however, behaves differently. The first overall 2e− oxidation underlying the first composite voltammetric wave very likely involves two opposing {Ru}−CHCH−C4H2S− COO− sides, thereby minimizing repulsive Coulombic forces.
Figure 1. Structure of 2-S as the benzene trisolvate: (a) top view; (b) side view. Solvent molecules other than the benzene molecule in the central cavity as well as H atoms are removed for reasons of clarity. Ellipsoids are displayed at the 50% probability level.
The macrocycle is almost planar with only a 2.7° tilt of the divinylthiophene linkers to above or below the plane defined by the ruthenium atoms and the thiophene-2,5-dicarboxylate linkers. The divinylthiophene diruthenium moieties adopt a cisoid conformation at the vinylic groups such that the sulfur atoms of all thiophene rings point inward into the central cavity. The latter has appropriate dimensions of 12.9 Å × 9.5 Å, as measured between opposing sulfur atoms, and hosts an almost coplanar benzene solvate molecule. The P−Ru−P vectors of neighboring vinylruthenium units are almost parallel with torsion angles of 2.6−7.2°. The electrochemical properties of 2-A and 2-S were studied by cyclic and square wave voltammetry. As depicted in Figure S15 in the Supporting Information, both isomers show a pattern of two consecutive, reversible redox processes that comprise two closely spaced 1e− waves each. In the CH2Cl2/nBu4NPF6 electrolyte B
DOI: 10.1021/acs.organomet.8b00057 Organometallics XXXX, XXX, XXX−XXX
Communication
Organometallics Thus, oxidized and reduced sides will alternate in 2-A2+. In situ oxidation of 2-A to 2-A2+ causes a shift of the prominent visible band from 398 to 467 nm and the growth of a weaker absorption at 744 nm (Figure 2, Figure S25 and Table S6 in the Supporting
observed for oxidized macrocycles 2-S and 2-A (see Figures S28 and S29 in the Supporting Information).17 They differ in slightly smaller g values of 2.012 and 2.023 for 2-S2+/4+ in comparison to 2.028 and 2.032 for 2-A2+/4+, which is again in line with a higher bridge contribution of the more conjugated 2-Sn+. The lesser degree of delocalization and the concomitant higher spin densities at individual atoms lead to discernible hyperfine splittings in 2-A2+/4+. They are, however, too poorly resolved to allow for an unambiguous assignment. Interestingly, and paralleling the behavior of divinylphenylene isophthalate-derived tetraruthenium macrocycles,13,14 both tetracations are EPR active even at room temperature, whereas the dication of precursor 1-S2+ exhibits no EPR signal.16 This unusual behavior warrants further studies and points to interesting magnetic properties of even the higher oxidized forms of such structures. In conclusion, constitutionally isomeric tetraruthenium macrocycles constructed from differently functionalized thiophene linkers display fundamentally different electrochemical and spectroscopic properties due to the different extensions of their π-conjugated sides. Mixed-valent 2-Sn+ (n = 1−3) are best described as consisting of two electronically strongly coupled but mutually insulated divinylthiophene diruthenium entities, whereas 2-An+ contains four electronically weakly coupled vinylthiophene ruthenium moieties.
■
Figure 2. Changes in the UV/vis/NIR spectra (top, left) and in the ν(CO) (top, right) and NIR (bottom) regions of the IR spectra upon stepwise oxidation of 2-A.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00057. Synthetic procedures, characterization data, NMR and mass spectra, cyclic and square wave voltammograms, results of IR and UV/vis/NIR spectroelectrochemical measurements with deconvolutions, and EPR spectra (PDF)
Information). The sizable blue shift and reduction in absorptivity of the low-energy electronic band in comparison to the 2-S2+ isomer are due to the confinement of the conjugated πchromophore of 2-An+ to only a monoruthenium vinylthiophene unit. Thus, the vis/NIR spectroscopic pattern of 2-A2+ closely resembles that of other styrylruthenium benzoate radical cations (e.g., λmax 403, 652 nm for Ph−CHCH−{Ru}−(κ-O,O′OOCPh)+).17 Simultaneously, the single Ru(CO) band of 2-A at 1904 cm−1 changes into a pattern of two separate bands at 1914 and 1966 cm−1, where the lower energy absorption represents the remaining reduced sides and the higher energy band the already oxidized sides. On further oxidation to 2-A4+ the Ru(CO) bands merge into a single absorption at 1978 cm−1 (Figure 2 and Table S6 in the Supporting Information). Most importantly, the mixed-valent intermediates 2-A+/2+/3+ display a weak yet clearly discernible intervalence charge-transfer (IVCT) band near 7000 cm−1 with maximum intensity for 2-A2+ (ν̃ 7165 cm−1, Δν̃1/2 = 3245 cm−1) as inferred from spectral deconvolution of chemically generated 2-A2+; see Figure 2 and Figure S26 in the Supporting Information). As in the previously reported triruthenium macrocycles with 5-vinylfuran-2-carboxylate or 3-ethynylbenzoate linkers,15 these bands are assigned to electronic through-bond coupling between neighboring reduced and oxidized {Ru}−CHCH−C4H2S−COO− units. These interactions also contribute to the blue shift of the low-energy Ru(CO) band and the red shift of the high-energy Ru(CO) band of 2-A2+ in comparison to 2-A and 2-A4+. No such effects were observed for 2-Sn+ due to the insulating properties of the thiophene-2,5-dicarboxylate linkers. All of the above conclusions have been corroborated by quantum chemical calculations. The latter also produce a low-energy NIR band for 2-A2+ with IVCT character, which has no counterpart in 2-S2+ (see Figure S27 in the Supporting Information for a charge density difference plot). As for other styryl ruthenium benzoate radical cations, only isotropic EPR spectra without resolved hyperfine splittings are
Accession Codes
CCDC 1819561 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail for R.F.W.:
[email protected]. ORCID
Rainer F. Winter: 0000-0001-8381-0647 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The authors thank Maximilian Dürr and Ivana IvanovićBurmazović from the Friedrich-Alexander Universität Erlangen-Nürnberg for the acquisition of the ESI-MS spectra.
■
REFERENCES
(1) Stricklen, P.; Verkade, J. Novel homo and heterometallic coordination macrocycles. J. Am. Chem. Soc. 1983, 105, 2494−2495. (2) (a) Smulders, M. M. J.; Riddell, I. A.; Browne, C.; Nitschke, J. R. Building on architectural principles for three-dimensional metallosupramolecular construction. Chem. Soc. Rev. 2013, 42, 1728−1754.
C
DOI: 10.1021/acs.organomet.8b00057 Organometallics XXXX, XXX, XXX−XXX
Communication
Organometallics (b) Ward, M. D.; Raithby, P. R. Functional behaviour from controlled self-assembly: challenges and prospects. Chem. Soc. Rev. 2013, 42, 1619−1636. (c) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Supramolecular coordination: self-assembly of finite two- and threedimensional ensembles. Chem. Rev. 2011, 111, 6810−6918. (d) Lippert, B.; Sanz Miguel, P. J. Metallatriangles and metallasquares: the diversity behind structurally characterized examples and the crucial role of ligand symmetry. Chem. Soc. Rev. 2011, 40, 4475−4487. (e) Han, Y.-F.; Jia, W.G.; Yu, W.-B.; Jin, G.-X. Stepwise formation of organometallic macrocycles, prisms and boxes from Ir, Rh and Ru-based half-sandwich units. Chem. Soc. Rev. 2009, 38, 3419−3434. (3) (a) Xu, L.; Wang, Y.-X.; Yang, H.-B. Recent advances in the construction of fluorescent metallocycles and metallocages via coordination-driven self-assembly. Dalton Trans. 2015, 44, 867−890. (b) Shanmugaraju, S.; Joshi, S. A.; Mukherjee, P. S. Self-assembly of metallamacrocycles using a dinuclear organometallic acceptor: synthesis, characterization, and sensing study. Inorg. Chem. 2011, 50, 11736−11745. (c) Shanmugaraju, S.; Bar, A. K.; Chi, K.-W.; Mukherjee, P. S. Coordination-Driven Self-Assembly of Metallamacrocycles via a New PtII2 Organometallic Building Block with 90° Geometry and Optical Sensing of Anions. Organometallics 2010, 29, 2971−2980. (d) Ghosh, S.; Chakrabarty, R.; Mukherjee, P. S. Design, synthesis, and characterizations of a series of Pt4 macrocycles and fluorescent sensing of Fe3+/Cu2+/Ni2+ through metal coordination. Inorg. Chem. 2009, 48, 549−556. (4) (a) Han, M.; Engelhard, D. M.; Clever, G. H. Self-assembled coordination cages based on banana-shaped ligands. Chem. Soc. Rev. 2014, 43, 1848−1860. (b) Mishra, A.; Kang, S. C.; Chi, K.-W. Coordination-Driven Self-Assembly of Arene-Ruthenium Compounds. Eur. J. Inorg. Chem. 2013, 2013, 5222−5232. (c) Schmidt, A.; Casini, A.; Kühn, F. E. Self-assembled M2L4 coordination cages. Coord. Chem. Rev. 2014, 275, 19−36. (d) Custelcean, R. Anion encapsulation and dynamics in self-assembled coordination cages. Chem. Soc. Rev. 2014, 43, 1813−1824. (5) (a) Horiuchi, S.; Murase, T.; Fujita, M. Diels-Alder reactions of inert aromatic compounds within a self-assembled coordination cage. Chem. - Asian J. 2011, 6, 1839−1847. (b) Nishioka, Y.; Yamaguchi, T.; Yoshizawa, M.; Fujita, M. Unusual 2 + 4 and 2 + 2 cycloadditions of arenes in the confined cavity of self-assembled cages. J. Am. Chem. Soc. 2007, 129, 7000−7001. (6) (a) Winter, R. F. The molecular electrochemistry of metal−organic metallamacrocycles. Curr. Op. Electrochem. 2018, 8, 14−23. (b) Croué, V.; Goeb, S.; Sallé, M. Metal-driven self-assembly: the case of redoxactive discrete architectures. Chem. Commun. 2015, 51, 7275−7289. (7) (a) Dinolfo, P. H.; Coropceanu, V.; Brédas, J.; Hupp, J. T. A New Class of Mixed-Valence Systems with Orbitally Degenerate Organic Redox Centers. Examples Based on Hexa-Rhenium Molecular Prisms. J. Am. Chem. Soc. 2006, 128, 12592−12593. (b) Dinolfo, P. H.; Lee, S. J.; Coropceanu, V.; Brédas, J.; Hupp, J. T. Borderline Class II/III LigandCentered Mixed Valency in a Porphyrinic Molecular Rectangle. Inorg. Chem. 2005, 44, 5789−5797. (c) Dinolfo, P. H.; Hupp, J. T. TetraRhenium Molecular Rectangles as Organizational Motifs for the Investigation of Ligand-Centered Mixed Valency: Three Examples of Full Delocalization. J. Am. Chem. Soc. 2004, 126, 16814−16819. (d) Dinolfo, P. H.; Williams, M. E.; Stern, C. L.; Hupp, J. T. RheniumBased Molecular Rectangles as Frameworks for Ligand-Centered Mixed Valency and Optical Electron Transfer. J. Am. Chem. Soc. 2004, 126, 12989−13001. (8) (a) Yang, H.-B.; Ghosh, K.; Northrop, B. H.; Stang, P. J. Selfrecognition in the coordination-driven self-assembly of three-dimensional M3L2 polyhedra. Org. Lett. 2007, 9, 1561−1564. (b) Das, N.; Arif, A. M.; Stang, P. J.; Sieger, M.; Sarkar, B.; Kaim, W.; Fiedler, J. SelfAssembly of Heterobimetallic Neutral Macrocycles Incorporating Ferrocene Spacer Groups: Spectroelectrochemical Analysis of the Double Two-Electron Oxidation of a Molecular Rectangle. Inorg. Chem. 2005, 44, 5798−5804. (c) Resendiz, M. J. E.; Noveron, J. C.; Disteldorf, H.; Fischer, S.; Stang, P. J. A self-assembled supramolecular optical sensor for Ni(II), Cd(II), and Cr(III). Org. Lett. 2004, 6, 651−653. (d) Kaim, W.; Schwederski, B.; Dogan, A.; Fiedler, J.; Kuehl, C. J.; Stang,
P. J. Metalla-Supramolecular Rectangles as Electron Reservoirs for Multielectron Reduction and Oxidation. Inorg. Chem. 2002, 41, 4025− 4028. (e) Vajpayee, V.; Bivaud, S.; Goeb, S.; Croué, V.; Allain, M.; Popp, B. V.; Garci, A.; Therrien, B.; Sallé, M. Electron-Rich Arene−Ruthenium Metalla-architectures Incorporating Tetrapyridyl−Tetrathiafulvene Donor Moieties. Organometallics 2014, 33, 1651−1658. (f) Yuan, M.; Weisser, F.; Sarkar, B.; Garci, A.; Braunstein, P.; Routaboul, L.; Therrien, B. Synthesis and Electrochemical Behavior of a Zwitterion-Bridged Metalla-Cage. Organometallics 2014, 33, 5043−5045. (g) Fujita, M.; Tominaga, M.; Hori, A.; Therrien, B. Coordination Assemblies from a Pd(II)-Cornered Square Complex. Acc. Chem. Res. 2005, 38, 369−378. (h) Mattsson, J.; Govindaswamy, P.; Renfrew, A. K.; Dyson, P. J.; Štěpnička, P.; Süss-Fink, G.; Therrien, B. Synthesis, Molecular Structure, and Anticancer Activity of Cationic Arene Ruthenium Metallarectangles. Organometallics 2009, 28, 4350−4357. (i) Hartmann, H.; Berger, S.; Winter, R.; Fiedler, J.; Kaim, W. Reversible and Site-Specific Reduction of the Ligand Sides in a Molecular Rectangle with up to Eight Electrons. Inorg. Chem. 2000, 39, 4977−4980. (9) (a) Wilson, L. E.; Hassenrück, C.; Winter, R. F.; White, A. J. P.; Albrecht, T.; Long, N. J. Ferrocene- and Biferrocene-Containing Macrocycles towards Single-Molecule Electronics. Angew. Chem., Int. Ed. 2017, 56, 6838−6842. (b) Hoffmann, V.; Le Pleux, L.; Häussinger, D.; Unke, O. T.; Prescimone, A.; Mayor, M. Deltoid versus Rhomboid. Organometallics 2017, 36, 858−866. (10) Szalóki, G.; Croué, V.; Carré, V.; Aubriet, F.; Alévêque, O.; Levillain, E.; Allain, M.; Aragó, J.; Ortí, E.; Goeb, S.; Sallé, M. Controlling the Host−Guest Interaction Mode through a Redox Stimulus. Angew. Chem., Int. Ed. 2017, 56, 16272−16276. (11) Croué, V.; Goeb, S.; Szalóki, G.; Allain, M.; Sallé, M. Reversible Guest Uptake/Release by Redox-Controlled Assembly/Disassembly of a Coordination Cage. Angew. Chem., Int. Ed. 2016, 55, 1746−1750. (12) (a) Schulze, M.; Kunz, V.; Frischmann, P. D.; Würthner, F. A supramolecular ruthenium macrocycle with high catalytic activity for water oxidation that mechanistically mimics photosystem II. Nat. Chem. 2016, 8, 576−583. (b) Kunz, V.; Schulze, M.; Schmidt, D.; Würthner, F. Trinuclear Ruthenium Macrocycles. ACS Energy Lett. 2017, 2, 288−293. (13) Fink, D.; Weibert, B.; Winter, R. F. Redox-active tetraruthenium metallacycles: reversible release of up to eight electrons resulting in strong electrochromism. Chem. Commun. 2016, 52, 6103−6106. (14) Scheerer, S.; Linseis, M.; Wuttke, E.; Weickert, S.; Drescher, M.; Tröppner, O.; Ivanovic-Burmazovic, I.; Irmler, A.; Pauly, F.; Winter, R. F. Redox-Active Tetraruthenium Macrocycles Built from 1,4Divinylphenylene-Bridged Diruthenium Complexes. Chem. - Eur. J. 2016, 22, 9574−9590. (15) Fink, D.; Bodensteiner, M.; Linseis, M.; Winter, R. F. Macrocyclic Triruthenium Complexes Having Electronically Coupled Mixed-Valent States. Chem. - Eur. J. 2018, 24, 992−996. (16) Pfaff, U.; Hildebrandt, A.; Korb, M.; Osswald, S.; Linseis, M.; Schreiter, K.; Spange, S.; Winter, R. F.; Lang, H. Electronically Strongly Coupled Divinylheterocyclic-Bridged Diruthenium Complexes. Chem. Eur. J. 2016, 22, 783−801. (17) Wuttke, E.; Hervault, Y.-M.; Polit, W.; Linseis, M.; Erler, P.; Rigaut, S.; Winter, R. F. Divinylphenylene- and EthynylvinylphenyleneBridged Mono-, Di-, and Triruthenium Complexes for Covalent Binding to Gold Electrodes. Organometallics 2014, 33, 4672−4686.
D
DOI: 10.1021/acs.organomet.8b00057 Organometallics XXXX, XXX, XXX−XXX
