Article pubs.acs.org/IC
Metal−Ligand Exchange in a Cyclic Array: The Stepwise Advancement of Supramolecular Complexity Manik Lal Saha and Michael Schmittel* Center of Micro- and Nanochemistry and Engineering, Organische Chemie I, Universität Siegen, Adolf-Reichwein-Strasse 2, D-57068 Siegen, Germany S Supporting Information *
ABSTRACT: Herein, we demonstrate how the supramolecular complexity (evaluated by the degree of self-sorting M) evolves in a chemical cycle of cascaded metallosupramolecular transformations, using abiological self-assembled entities as input signals. Specifically, the successive addition of the supramolecular self-assembled structures S1 and (T2 + S2) to the starting supramolecular two-component equilateral triangle T1 (M = 1) first induced a fusion into the three-component quadrilateral R1 (M = 6) and then to the five-component scalene triangle T3 (M = 16). Upon the addition of the supramolecular input M1 to T3, a notable self-sorting event occurred, leading to regeneration of the triangle T1 along with formation of the scalene triangle T4 (M = 25). This last step closed the cycle of the supramolecular transformations.
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In the final step of the cycle, an intricate supramolecule is released as the only product, while the initial “supramolecular template” is regained in 75% yield. In this respect, each transformation in the reaction cycle sheds some light on the basic principles guiding the reshuffling of multicomponent aggregates, like the reconfiguration of multiprotein complexes in the cell. In the RAB cycle,8 for instance, equally a signal output is produced after running through a series of self-assembled protein aggregates. The new cycle is purely thermodynamically controlled and establishes a proof-of-concept for chemical loops outside the kinetically controlled world. At the same time, the advancement of the supramolecular complexity through cascaded selfassembly has also been realized for the first time. In comparison to other supramolecular transformations,1,2 such as the two-state stimulus-responsive reorganization of supramolecules by changes of the connectivity and binding patterns through either light,16−18 chemical,19−30 or redox input,31,32 the implementation of a cascaded cyclic supramolecular transformation9,12 perceptibly demands an exceptional design for merging, rearranging, and breaking up self-assemblies. To solve the thermodynamic issues of a cyclic scheme as described in Figure 1a, we considered three possible scenarios (Figure 1b, cases I−III). The thermodynamic course sketched in case I identifies step 3 as the key reaction, in which a strong downhill transformation drives the uphill reaction, leading to regeneration of the high-energy assembly A. Specifically, the
INTRODUCTION The intricate dynamic exchange processes happening between homo- and heterooligomeric protein complexes find some analogy in the reshuffling of supramolecular aggregates,1,2 especially in the subfield of supramolecular fusion and fission. While several cases of directed fusion of simple into intricate heteroleptic metallosupramolecular aggregates in one-pot procedures have been reported by Stang et al.,3 Newkome et al.,4 Chand et al.,5,6 and us,7 a multistep transformation of selfassembled structures, remotely similar to the protein shuffling in the RAB cycle,8 is known from a seminal contribution by Nitschke et al.9 In their work, the successive addition of first copper(I) and then zinc(II) ions and finally 8-aminoquinoline to a three-component mixture led to a sequence of incomplete and then completive and finally incomplete self-sorting events.10,11 The process was described as a small step toward signaling systems, as known in nature. Lately, in a follow-up work, Nitschke et al. used small molecules as inputs to demonstrate a spectacular network of selective transformations, involving homoleptic structures.12 As before, the transformations were based on incomplete self-sorting, so that the “waste” of the subcomponent exchange was enriched in solution with each transformation. In contrast, the cyclic set of supramolecular transformations designed below (Scheme 1) is based on completive self-sorting events, with all inputs themselves being supramolecular aggregates. In this unprecedented three-step reaction cycle, each transformation involves two multicomponent aggregates and generates product(s) with an increase in the supramolecular complexity,13−15 as evaluated by the degree of self-sorting M10,11 (vide infra). © XXXX American Chemical Society
Received: September 20, 2016
A
DOI: 10.1021/acs.inorgchem.6b02256 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry Scheme 1. Chemical Cycle of Supramolecular Transformations
furnishes the initial A without the need of a coupled energy transfer. In a pragmatic approach, both concepts (cases I and III) may also be applied together in a hybrid method, as demonstrated in case II. For the present cycle of supramolecular transformations, we followed the schematics of case I (Figure 1b). Because each step
high-energy input D is used to generate the low-energy product BCD and the starting self-assembly A. Alternatively, one may use high-energy inputs B−D in each step (case III), so that the products always gain extra energy with regard to the initial assembly A. At the end, the removal of all stimuli as the product BCD B
DOI: 10.1021/acs.inorgchem.6b02256 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 1. (a) General representation of a cyclic cascaded transformation and (b) three possible qualitative thermodynamic scenarios. The successive addition of supramolecular inputs B and C into the starting assembly A induces at first a linear cascaded fusion sequence (A → AB → ABC). Further addition of the input D to the resultant assembly ABC causes regeneration of A along with formation of the product BCD.
in the cycle of Figure 1a will bring together more components, thereby each supramolecular product should increase in complexity. At present, the state-of-the-art multicomponent selfassembly is a seven-component aggregate.33 We considered limiting our cyclic transformation protocol, though, to a five-component assembly because it is much easier to control.34 The result of our considerations is shown in Scheme 1. The supramolecular cycle involves the sequential addition of three supramolecular inputs to the equilateral triangle T1 as our starting point, thereby triggering multiple disassembly/reassembly events. At the end of the cyclic cascade, the initial assembly T1 is restored while a product is released that is a combination of all added stimuli, i.e., the scalene triangle T4.
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Chart 1. (a) Model Ligands and (b) Complexes Used in the Present Study
RESULTS AND DISCUSSION
In order to preevaluate the individual steps of Scheme 1, we first examined the design by studying the transformations using the mononuclear cornerstones, i.e., C1−C4-type cornerstones (Chart 1), contained in the various self-assemblies T1, S1, a T2 + S2 mixture, and M1. Accordingly, we needed to evaluate the reaction C1 + C2 → 2C5, mimicking step 1 of Scheme 1. First, the bis(iminopyridine)copper(I) complex C1 = [Cu(1)2]PF6 (log βC1 ≈ 11.5)35 and the front-strain-loaded complex C2 = [Cu(2)2]PF6 were prepared and fully characterized. The spectroscopic data of these complexes are given and discussed in the Supporting Information (SI). Despite their visible bulk, the dimethoxyaryl groups in 2 do not prevent the formation of complex C2 on steric grounds, while its reduced association constant (log βC2 ≈ 9.4; see the SI) indicates a significant amount of front strain present in the complex. We thus expected that C2 has a large propensity to form the strong heteroleptic complex C5 = [Cu(1)(2)]PF6 (log βC5 ≈ 11.8; see the SI) in the presence of the homoleptic copper(I) complex C1 (Scheme 2, paths a and b). Indeed, a 1:1 mixture of C1 and C2 furnished C5, the mononuclear cornerstone of R1 (Scheme 1, step 1), within a minute at 25 °C, as evidenced by all spectroscopic data (see the SI). The fusion process C1 + C2 → 2C5 (ΔGR = −1.8 kcal mol−1 per mole of C5) mainly relies on the proper steric programming, but it is additionally guided by maximum site occupancy36 and
Scheme 2. Multiple Self-Sorting Protocols with Mononuclear Model Complexes
HETPHEN37,38 (HETeroleptic bis-PHENanthroline complexes) control. C
DOI: 10.1021/acs.inorgchem.6b02256 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry For an evaluation of step 2 (Scheme 1), the heteroleptic pentacoordinated zinc(II) complex C3 = [Zn(3)(4)](OTf)2 was required. It cleanly formed from a 1:1:1 mixture of its constituents without any problem (log βC3 ≈ 12.4)39 and being in full agreement with its HETTAP (HETeroleptic Terpyridine And Phenanthroline complexes) design.40 Clearly, the finely tuned balance of steric and electronic effects in phenanthroline 3, emerging from its two bulky 2,9-dimesityl substituents, guides the exclusive formation of the HETTAP complex C3. To preassess step 2 of the cycle, i.e., clean formation of T3, the required self-sorting through reshuffling of the constituents41 (2C5 + C3 → C5 + C6 + C7) needed to be investigated in a stoichiometry-dependent manner (Scheme 2, paths c−e). This is because the integrity of T3 relies not only on the clean formation of the new cornerstones C6 and C7 but equally on their modulated orthogonality42 toward complex C5. The difficulty here is that 50% of C5 needs to be maintained, while the other 50% is a required partner in step 2. On the basis of our prior knowledge, we anticipated that C3 and C5 may undergo reshuffling of their constituents already at room temperature.7 Indeed, upon their mixing in a 1:1 ratio at 25 °C, clean formation of C6 = [Zn(2)(4)](OTf)2 and C7 = [Cu(1)(3)]PF6 was observed after ca. 40 min, as evidenced by 1H NMR analysis (path c). In the required stoichiometry, mimicking the situation in step 2 of Scheme 1, the reaction at a ratio of C5:C3 = 2:1 furnished a mixture of C5, C6, and C7 in a 1:1:1 ratio after ca. 15 min at 25 °C (path d). Interestingly, in this high-fidelity ligand exchange, both HETPHEN complexes C5 (log βC5 ≈ 11.8) and C7 (log βC7 ≈ 11.3)43 have similar association constants.44 Thus, it is most likely the high stability of complex C6 (log βC6 ≈ 14.4)39 that drives the observed ligand shuffling C3 + C5 → C7 + C6 (ΔGR = −2.0 kcal mol−1). Looking more into details, we suggest that the additional zinc(II)···OMe ion−dipole interaction present in C6 complementing hexacoordination33 at the Zn2+ ion increases the stability of C6 in comparison to that of C3 (only pentacoordinated Zn2+ ions).40 For step 3 of Scheme 1, we decided to interrogate the transformation C4 + C5 + C7 → C1 + C6 + C8 at the mononuclear level. Unfortunately, a clean preparation of C4 = [Zn(4)(5)](OTf)2, representing the mononuclear corner of M1, was not possible. Rather, all possible homoleptic combinations (=[Zn(4)2](OTf)2, [Zn(5)2](OTf)2, and [Zn(5)3](OTf)2) and the heteroleptic complex C4 emerged from a 1:1:1 mixture of 4, 5, and Zn(OTf)2 (see the SI). Because of the unavailability of pure C4 = [Zn(4)(5)](OTf)2, we were not able to evaluate the required binding constant experimentally but instead utilized a thermochemical cycle calculation, furnishing log βC4 ≈ 10.9.45 With all association constants known, the transformation C4 + C5 + C7 → C1 + C6 + C8 is exergonic by ΔGR = −1.9 kcal mol−1. The required orthogonality was already warranted from our earlier findings.44 To obtain the fidelity in the multiple fusion processes as required in Scheme 1, it is not sufficient to rely solely on the complexation selectivity seen with the mononuclear cornerstones. Additionally, positional control by the ligands 6−9 (Scheme 3) in the supramolecular aggregates is very essential. Thus, we implemented the ligands 3 and 4 as the termini of the new phenanthroline−terpyridine hybrid 6, readily synthesized by a Sonogashira cross-coupling reaction. The complexation properties of 1 were ingrained into bis(iminopyridine) 9, carrying decyloxy groups to increase the solubility. Along some well-known synthetic procedures, the information contained in
Scheme 3. Chemical Structures of Ligands 6−9
(4 + 5) and 2 was amalgamated into the ditopic ligands 7 and 8, respectively (Scheme 3).44 At this stage, we had to prepare the various supramolecular structures that served as either starting points or inputs in the fusion cycle, i.e., T1, S1, T2, and M1, shown in Scheme 1. As expected from the design criteria, the reaction between ligand 9 and [Cu(CH3CN)4]PF6 (1:1) produced the triangular assembly T1 = [Cu3(9)3](PF6)3 as the unique product. The electrospray ionization mass spectrometry (ESI-MS) spectrum of the reaction mixture exhibited two major peaks at m/z 948.4 and 1495.0 for [Cu3(9)3]3+ and [Cu3(9)3](PF6)2+, respectively, which clearly supported the integrity of T1. A single diffusion coefficient in the DOSY NMR as well as a single set of signals in the 1H NMR provided evidence for its purity (see the SI). The reaction of 8 and [Cu(CH3CN)4]PF6 (1:1) furnished the assembly S1 = [Cu4(8)4](PF6)4 in a fashion similar to that observed in analogous reaction systems with bisphenanthrolines and Cu+ ions.46 Indeed, solution NMR and the diagnostic ESI-MS peaks at m/z 1402.9 and 1919.3 for [Cu4(8)4]4+ and [Cu4(8)4](PF6)3+, respectively, confirmed the identity of S1.47 Following a protocol similar to the preparation of T1 and S1, we received a 2:1 mixture of triangle T2 = [Zn3(6)3](OTf)6 and quadrilateral S2 = [Zn4(6)4](OTf)8 from ligand 6 and Zn(OTf)2 (1:1), as evidenced by 1H NMR and ESI-MS data as well as further supported by earlier findings.48−50 Finally, the sterically loaded input M1 was prepared by reacting 7 with Zn(OTf)2 (1:1; see the SI). The ESI-MS analysis showed the presence of four isotopically well-resolved major peaks at m/z 288.3, 433.7, 726.4, and 1601.9, representing [Zn2(7)2]4+, [Zn2(7)2](OTf)3+, [Zn2(7)2](OTf)22+, and [Zn2(7)2](OTf)3+, respectively.51 Considering the vastly different 1H NMR shifts of protons 2-H and 9-H (see the experimental part), the structure of M1 = [Zn2(7)2](OTf)4 is well corroborated. Earlier work by Sauvage et al. had demonstrated the formation of a related dimeric zinc(II) complex from a ditopic ligand equally containing 1,10-phenanthroline and terpyridine units but with a different spacer.52 Taking the reported complex as a reference allowed unambiguous assignment of the 1H NMR data (see the Experimental Section). The strain and heteroleptic complexation at the zinc(II) centers in M1 may be apprehended based on Sauvage et al.’s reasoning52 that the alternative hexacoordinated zinc(II) bis(terpyridine) complexation would generate an assembly at high entropic costs. D
DOI: 10.1021/acs.inorgchem.6b02256 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
3M1 + 6T3 → 6T4 + 2T1 (ΔGstep 3 = −1.8 kcal mol−1 with respect to the formation of one entity of T4). As the strain contained in M1 is not yet considered in our estimate of ΔGstep 3, step 3 should have even more driving force than −1.8 kcal mol−1. Thus, the scalene triangle T4 = [Zn2Cu(6)(7)(8)](OTf)4(PF6)2 and the starting triangular assembly T1 should emerge readily. To elucidate the outcome and efficiency of step 3 in the fusion cycle (Scheme 1), we independently synthesized and characterized the pure scalene triangle T4 as a reference (see the SI). To check for step 3, we added 0.50 equiv of M1 to a preequilibrated solution of T3 (1 equiv) and refluxed it in acetonitrile for 3 h to achieve full thermodynamic equilibration. 1H NMR spectra of the reaction mixture confirmed the formation of T4 with an additional set of peaks corresponding to T1 as major products (Figure 2). Because of the broad 1H signals, we suppose that the final step was not quantitative. Approximately 25% (based on the 1 H NMR)54 of our starting assemblies T3 and M1 was detected. While the ESI-MS data proved the formation of T1 and T4 as the only products by showing isotopically well-resolved signals from both assemblies, some other peaks provided evidence for the presence of unreacted T3 and M1 (see the SI, Figure S60). On the basis of the observed data, we estimate that the transformation stops at 75 ± 5%; i.e., 75% of T1 is regained from T3. Apparently, the thermodynamic driving force for 3M1 + 6T3 → 6T4 + 2T1 is not sufficient to fully propel the transformation to completion. Nevertheless, the present findings convincingly support for the first time the existence of a full cycle of supramolecular transformations.
Having now access to the starting assembly T1 and all required inputs, we were ready to interrogate the full cyclic process as presented in Scheme 1. At the start, S1 was added to a solution of preassembled T1 at a ratio of 3:4 S1/T1. To our delight, all spectroscopic techniques (see the SI) suggested clean formation of the quadrilateral R1 = [Cu4(8)2(9)2](PF6)4 after ca. 10 min at 25 °C. For instance, the ESI-MS spectrum of the mixture exhibited no more signals corresponding to S1 or T1, but only peaks at m/z 1175.5 and 1615.7, representing [Cu4(8)2(9)2]4+ and [Cu4(8)2(9)2](PF6)3+, respectively, being in full agreement with the newly formed R1. Furthermore, the identity and purity of R1 was corroborated by 1H−1H COSY and DOSY NMR as well as elemental analysis. In the ensuing step, the next input, the preequilibrated T2 and S2 (2:1) mixture, was added to 0.50 equiv of R1 (with respect to the initial amount of ligand 6 in the T2 + S2 mixture). After the solution was heated at 60 °C for 2 h, the product analysis of the crude mixture by ESI-MS suggested clean formation of the scalene triangle T3 = [ZnCu2(6)(8)(9)](OTf)2(PF6)2. The MS spectrum indeed revealed only major peaks at m/z 791.4, 1104.1, and 1728.6, representing [ZnCu2(6)(8)(9)]4+, [ZnCu2(6)(8)(9)](OTf)3+, and [ZnCu2(6)(8)(9)](OTf)(PF6)2+, respectively. Furthermore, the identity and purity of T3 was confirmed by 1H and DOSY NMR as well as elemental analysis. At this juncture, it would be useful to know the driving force ΔGR of the reactions in steps 1 and 2 (Scheme 1). However, a direct measurement of ΔGR for those steps, e.g., by UV−vis or isothermal titration calorimetry, would be rather cumbersome because of the complexity and the different kinetics of the individual self-assembly steps. As a way out, we have semiquantitatively evaluated the process based on the association constants of the mononuclear cornerstones, assuming that the self-assemblies S1, T1, etc., do not experience strain otherwise.53 In addition, the energetics was assessed without entropic correction because the number of assemblies does not change significantly in the individual processes. Using such simplifications, the first two steps of the cycle are exergonic, i.e., 4T1 + 3S1 → 6R1 by ΔGstep 1 = −7.4 kcal mol−1 (with respect to the formation of one entity of R1) and (2T2 + S2) + 5R1 → 10T3 by ΔGstep 2 = −2.1 kcal mol−1 (with respect to the formation of one entity of T3). In order to run a cyclic supramolecular fusion protocol, we decided to regenerate T1 from T3. Because T3 had formed in two exergonic reactions from T1 (see Figure 1, case I), the regeneration of T1 would require some high-energy input to render the step 3 exergonic. We reasoned that the addition of the dimeric M1 to T3 may induce the supramolecular transformation
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CONCLUSION In summary, we describe here the first cycle involving a series of supramolecular transformations. In light of the general importance of chemical loops for life, this purely thermodynamically controlled cycle establishes a proof-of-concept for chemical loops outside the kinetically controlled world and adds new facets to our understanding of the guided emergence of the supramolecular complexity.55 According to a formula presented earlier,10 the level of self-sorting M and thus the complexity increase from T1 (M = 1) and S1 with each step of the cycle via R1 (M = 6), T3 (M = 16), and finally to T4 (M = 25) (Scheme 4). It is interesting to note that the high M of T4 is balanced in the last step by the low complexity in T1 (M = 1). Each of the involved structures serves as a template for the more intricate follow-up structure. Although each supramolecular entity of our cycle may be generated independently from its constituents, the loop describes how the complexity
Figure 2. Partial 1H NMR spectra (400 MHz, 298 K) of (a) T1 (CD2Cl2:CD3CN = 19:1), (b) T4 (CD2Cl2:CD3CN = 1:19), and (c) a 1:2 mixture of M1 and T3 (CD2Cl2:CD3CN = 1:19), after 3 h reflux. The comparison of the spectra suggests that both triangles, i.e., the starting complex T1 as well as the scalene triangle T4, are regained in part c. The shift of proton k-H (Scheme 3) of T1 (d, J = 8.8 Hz) at 6.53 ppm is solvent-dependent. E
DOI: 10.1021/acs.inorgchem.6b02256 Inorg. Chem. XXXX, XXX, XXX−XXX
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Scheme 4. Increasing the Level of Complexity in the Three-Step Supramolecular Transformation As Judged by the Degree of SelfSorting Ma
a
The boxes show a summary of the possible constitutional options for R1, T3, and T4.
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may advance in discrete steps depending on the availability of inputs. As such, each structure represents a waiting state until the next building block becomes available, a scenario that may even have been crucial for evolving self-assemblies in prebiotic times. The present cycle demonstrates that multistep supramolecular transformations can be mastered with rather complex multicomponent structures. With a look at the famous RAB cycle, our next goal is thus to use the principles elaborated in the present work for driving the conversion between supramolecular machinery. Considering the recent advancements in the field of multicomponent rotors,56 such transformations should not be impossible to reach.
EXPERIMENTAL SECTION
General Procedures. All commercial reagents were used without further purification. Solvents were dried with appropriate desiccants and distilled prior to use. Silica gel (60−230 mesh) was used for column chromatography. Unless mentioned, 1H and 13C NMR were measured at 298 K on a Bruker Avance 400 MHz or a Varian VNMR-S 600 MHz spectrometer. Residual solvent signals were used as internal references. The following abbreviations were utilized to describe peak patterns: s = singlet, d = doublet, t = triplet, dd = doublet of doublets, td = triplet of doublets, dt = doublet of triplets, ddd = doublet of doublet of doublets, br = broad, brs = broad singlet, and m = multiplet. A detailed assignment of the protons is given in the SI. DOSY NMR data and all kinetic data were recorded on a Varian VNMR-S 600 MHz spectrometer. DOSY measurements were carried out at room temperature using the F
DOI: 10.1021/acs.inorgchem.6b02256 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry “Dbppste” pulse sequence from the Varian library. UV−vis spectra were recorded on a Varian Cary 100 Bio UV−vis spectrometer. Binding constants were determined using the SPECFIT/32 global analysis system by Spectrum Software Associates (Marlborough, MA).57,58 ESIMS spectra were recorded on a Thermo-Quest LCQ Deca. Melting points were measured on a Büchi SMP-20 instrument. IR spectra were recorded using a Varian 1000 FT-IR instrument. Elemental analysis measurements were done using the EA 3000 CHNS. Complexes C3,7 C6,7 C7,43 and C8,7 and ligands 1,43 2 and 3,44 7 and 8,44 as well as 1044 and 1144 (precursors for 6) and 1259 (precursors for 9) were synthesized as described earlier. Ligand 6. In an oven-dried glass tube with a side arm, 3-ethynyl-2,9dimesityl[1,10]phenanthroline (10; 106 mg, 241 μmol), 4′-(4iodophenyl)[2,2′:6′,2″]terpyridine (11; 95.0 mg, 218 μmol), TBAF· 3H2O (207 mg, 656 μmol), and PdCl2(PPh3)2 (4.00 mg, 5.70 μmol) were combined under a nitrogen atmosphere. The solid mixture was then stirred at 80 °C for 12 h under nitrogen. After cooling to room temperature, the residue was dissolved in dichloromethane (DCM) and washed once with KOH (1 N, 100 mL) and then successively with H2O.60 After drying over Na2SO4, the solvent was evaporated to furnish the crude product. The desired compound 6 was obtained as a paleyellow solid after purification by column chromatography (SiO2; DCM:EtOAC = 2:1). Yield: 35%. Mp: 220 °C. 1H NMR (400 MHz, CD2Cl2): δ 8.75 (s, 2 H), 8.72 (ddd, 3J = 4.8 Hz, 4J = 1.6 Hz, 5J = 1.0 Hz, 2 H), 8.69 (dt, 3J = 8.0 Hz, 4J = 1.0 Hz, 5J = 1.0 Hz, 2 H), 8.54 (s, 1 H), 8.34 (d, 3J = 8.4 Hz, 1 H), 7.95−7.88 (m, 4 H), 7.85 (d, 3J = 8.4 Hz, 2 H), 7.58 (d, 3J = 8.4 Hz, 1 H), 7.39 (ddd, 3J = 7.6 Hz, 3J = 4.8 Hz, 4 J = 1.0 Hz, 2 H), 7.33 (d, 3J = 8.4 Hz, 2 H), 7.03 (s, 2 H), 6.96 (s, 2 H), 2.41 (s, 3 H), 2.34 (s, 3 H), 2.08 (s, 6 H), 2.06 (s, 6 H). 13C NMR (100 MHz, CD2Cl2): δ 162.2, 160.9, 156.5, 156.3, 149.5, 149.4, 146.4, 145.4, 139.0, 138.9, 138.4, 138.0, 137.8, 137.4, 137.2, 136.4, 136.3, 136.1, 132.5, 128.6, 128.3, 128.0, 127.6, 127.3, 127.3, 126.0, 125.2, 124.3, 123.8, 121.5, 120.0, 118.8, 94.8, 88.6, 21.4, 21.2, 20.4, 20.0. IR (KBr): ν 3416, 3053, 2919, 2852, 2204, 1699, 1589, 1463, 1387, 1109, 1033, 909, 846, 791, 741,692, 617. ESI-MS: m/z 748.8 (100%; [M + H]+). Anal. Calcd for C53H41N5·2.75CH2Cl2: C, 68.22; H, 4.78; N, 7.14. Found: C, 68.26; H, 4.76; N, 7.31. Ligand 9. An oven-dried 50 mL round-bottomed flask was charged with 5,5′-[2,5-bis(decyloxy)-1,4-phenylene]bis(ethyne-2,1-diyl)dipicolinaldehyde (12; 27.0 mg, 41.6 μmol) and N,N-dimethyl-1,4benzenediamine (13; 74.0 mg, 543 μmol). After the addition of methanol (10 mL), the mixture was refluxed for 3 h. The reaction mixture was then cooled to room temperature, and the solid residue was collected by filtration, washed several times with methanol, and dried under vacuum to furnish the target compound as an orange solid. Yield: 92%. Mp: 123 °C. 1H NMR (400 MHz, CD2Cl2:CD3CN = 4:1): δ 8.78 (dd, 4J = 2.0 Hz, 5J = 0.8 Hz, 2 H), 8.65 (brs, 2 H), 8.19 (dd, 3J = 8.4 Hz, 5 J = 0.8 Hz, 2 H), 7.88 (ddd, 3J = 8.4 Hz, 4J = 2.0 Hz, 5J = 0.4 Hz, 2 H), 7.37 (d, 3J = 9.2 Hz, 4 H), 7.08 (s, 2 H), 6.75 (d, 3J = 9.2 Hz, 4 H), 4.06 (t, 3J = 6.4 Hz, 4 H), 3.00 (s, 12 H), 1.88−1.83 (m, 4 H), 1.60−1.53 (m, 4 H), 1.43−1.27 (m, 24 H), 0.86 (t, 3J = 7.2 Hz, 6 H). 13C NMR (100 MHz, CD2Cl2): δ 154.7, 154.3, 154.1, 152.1, 150.7, 139.2, 138.9, 123.3, 121.1, 120.5, 117.0, 114.1, 112.7, 92.4, 90.9, 69.9, 40.6 (NMe2), 32.2, 30.0, 29.9, 29.7, 29.7, 29.6, 26.4, 23.0, 14.2. IR (KBr): ν 2919, 2848, 2202, 1705, 1615, 1566, 1510, 1468, 1416, 1355, 1273, 1227, 1161, 1124, 1025, 944, 850, 772, 722, 642, 547. ESI-MS: m/z 885.7 (100%; [M + H]+). Anal. Calcd for C58H72N6O2·2CH2Cl2: C, 68.30; H, 7.26; N, 7.97. Found: C, 68.69; H, 7.29; N, 8.03. Equilateral Triangle T1 = [Cu3(9)3](PF6)3. In an NMR tube, [Cu(MeCN)4]PF6 (355 μg, 0.95 μmol) and 1,4-bis(decyloxy)-2,5bis[2-[[[[(p-(N,N-dimethylamino)phenyl]imino]methyl]pyridin-5yl]ethynyl]benzene (9; 843 μg, 0.95 μmol) were dissolved in 500 μL of CD2Cl2/CD3CN (4:1). The resultant suspension was kept in an ultrasonic bath for 2 h and the final solution subjected to analytical characterization without any further purification. Yield: quantitative. Mp: >250 °C. 1H NMR [400 MHz, CD2Cl2/CD3CN (4:1)]: δ 8.94 (s, 6 H), 8.52 (brs, 6 H), 8.05 (d, 3J = 8.0 Hz, 6 H), 7.86 (d, 3J = 8.0 Hz, 6 H), 7.42 (d, 3J = 8.8 Hz, 12 H), 6.93 (s, 6 H), 6.58 (d, 3J = 8.8 Hz, 12 H), 3.90 (t, 3J = 6.0 Hz, 12 H), 2.94 (s, 36 H), 1.72−1.66 (m, 12 H), 1.41−1.34 (m, 12 H), 1.23−1.13 (m, 72 H), 0.79 (t, 3J = 6.8 Hz, 18 H).
C NMR [150 MHz, CD2Cl2/CD3CN (4:1)]: δ 154.0, 151.8, 151.2, 150.7, 148.2, 139.7, 134.6, 126.4, 124.7, 124.0, 124.0, 113.7, 112.1, 93.3, 91.2, 69.5, 40.1, 32.1, 29.6, 29.6, 29.5, 29.2, 29.1, 25.9, 22.8, 14.1. IR (KBr): ν 3438, 2924, 2855, 2207, 1612, 1569, 1518, 1467, 1367, 1218, 1165, 1118, 1022, 945, 843, 556. ESI-MS: m/z 948.4 (100%; [M − 3PF6]3+), 1495.0 (10%; [M − 2PF6]2+). Anal. Calcd for C174H216Cu3F18N18O6P3·CH2Cl2: C, 62.44; H, 6.53; N, 7.49. Found: C, 62.74; H, 6.51; N, 7.88. Quadrilateral S1 = [Cu4(8)4](PF6)4. 3-[2-[4-[2-[2,9-Bis(2,6-dimethoxyphenyl)-1,10-phenanthrolin-3-yl]ethynyl]-2,5-bis(decyloxy)phenyl]ethynyl]-2,9-bis(2,6-dimethoxyphenyl)[1,10]phenanthroline (8; 4.94 mg, 3.69 μmol) and [Cu(MeCN)4]PF6 (1.37 mg, 3.69 μmol) were refluxed in 5 mL of 1,2-dichloroethane for 2 h. The reaction mixture was then cooled to room temperature, and the solvent was removed under reduced pressure. The resultant mixture was subjected to analytical characterization without any further purification. Yield: quantitative. Mp: >250 °C. IR (KBr): ν 3436, 2927, 2852, 2206, 1594, 1471, 1394, 1253, 1212, 1115, 1051, 807, 750, 558. ESI-MS: m/z 1402.9 (100%; [M − 4PF6]4+), 1919.3 (10%; [M − 3PF6]3+). Anal. Calcd for C344H360Cu4F24N16O40P4·2CH2Cl2: C, 65.32; H, 5.77; N, 3.52. Found: C, 65.35; H, 5.78; N, 3.55. A detailed 1H NMR characterization of S1 is given in the SI. Quadrilateral R1 = [Cu4(8)2(9)2](PF6)4. CD2Cl2 250 (μL) was added to S1 (1.31 mg, 0.21 μmol) and T1 (923 μg, 0.28 μmol) in an oven-dried 5 mL flask. A portion of the solution was monitored at 25 °C for 1 h in the NMR machine: the transformation was completed within 10 min. Yield: quantitative. Mp: >250 °C. ESI-MS: m/z 1175.5 (65%; [M − 4PF6]4+), 1615.7 (100%; [M − 3PF6]3+). Anal. Calcd for C288H324Cu4F24N20O24P4·4CH2Cl2: C, 62.37; H, 5.95; N, 4.98. Found: C, 62.35; H, 5.64; N, 4.79. Detailed 1H NMR characterization of R1 is given in the SI. Equilateral Triangle T2 = [Zn3(6)3](OTf)6 and Quadrilateral S2 = [Zn4(6)4](OTf)8. In an oven-dried 10 mL single-neck round-bottomed flask, a solution of 4′-[4-(2,9-dimesityl[1,10]phenanthrolin-3ylethynyl)phenyl][2,2′:6′,2″]terpyridine (6; 3.02 mg, 4.03 μmol) and Zn(OTf)2 (1.47 mg, 4.03 μmol) in acetonitrile was refluxed for 1 h. The solvent was evaporated from the light-yellow solution and the solid subjected to analytical characterization without any further purification. The 1H NMR analysis (600 MHz, CD3CN) indicated the formation of two assemblies (T2/S2) in a ratio of 2:1: T2. 1H NMR: δ 9.23 (s, 3 H), 9.18 (d, 3J = 8.4 Hz, 3 H), 8.67−8.55 (m, 12 H), 8.54 (s, 6 H), 8.30−8.26 (m, 6 H), 8.23 (d, 3J = 8.4 Hz, 3 H), 7.94 (d, 3J = 9.0 Hz, 6 H), 7.82 (d, 3J = 4.8 Hz, 6 H), 7.52−7.50 (m, 6 H), 7.37 (d, 3J = 9.0 Hz, 6 H), 6.23 (s, 6 H), 6.12 (s, 6 H), 1.74 (s, 9 H), 1.43 (s, 9 H), 1.24 (s, 18 H), 1.11 (s, 18 H). S2. 1H NMR: δ 9.30 (s, 4 H), 9.16 (d, 3J = 8.4 Hz, 4 H), 8.67−8.55 (m, 24 H), 8.30−8.26 (m, 8 H), 8.20 (d, 3J = 8.4 Hz, 4 H), 8.04 (d, 3J = 9.0 Hz, 8 H), 7.80 (d, 3J = 4.8 Hz, 8 H), 7.52−7.50 (m, 8 H), 7.41 (d, 3J = 9.0 Hz, 8 H), 6.23 (s, 8 H), 6.19 (s, 8 H), 1.67 (s, 12 H), 1.62 (s, 12 H), 1.17 (s, 24 H), 1.15 (s, 24 H). ESI-MS (T2): m/z 406.4 (30%; [M − 6OTf]6+), 517.2 (90%; [M − 5OTf]5+), 684.2 (60%; [M − 4OTf]4+), 1517.7 (8%; [M − 2OTf]2+). ESI-MS (S2): m/z 592.0 (55%; [M − 6OTf]6+), 739.9 (20%; [M − 5OTf]5+), 1332.8 (18%; [M − 3OTf]3+). ESI-MS signals shared by both T2 and S2: m/z 962.5 (100%; T2/ [M − 3OTf]3+ + S2/[M − 4OTf]4+). Scalene Triangle T3 = [ZnCu2(6)(8)(9)](OTf)2(PF6)2. In an ovendried 10 mL flask, a mixture 6 (1.09 mg, 1.46 μmol) and Zn(OTf)2 (530 μg, 1.46 μmol) was dissolved in 5 mL of acetonitrile and refluxed for 1 h. To the mixture was added solid R1 (3.85 mg, 0.730 μmol), and the resultant mixture was further refluxed for 2 h. The solvent was evaporated from the red solution and the solid subjected to analytical characterization without any further purification. Yield: quantitative. Mp: >250 °C. IR (KBr): ν 3437, 2925, 2854, 1611, 1590, 1506, 1472, 1367, 1257, 1163, 1112, 1031, 843, 639, 558. ESI-MS: m/z 791.4 (10%; [M − 2OTf, 2PF6]4+), 1104.1 (100%; [M − OTf, 2PF6]3+), 1728.6 (12%; [M − OTf, PF6]2+). Anal. Calcd for C199H203Cu2F18N15O18P2S2Zn·2CH2Cl2: C, 61.53; H, 5.32; N, 5.36; S, 1.63. Found: C, 61.40; H, 5.30; N, 5.26; S, 1.65. The 1H NMR of T3 is 13
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DOI: 10.1021/acs.inorgchem.6b02256 Inorg. Chem. XXXX, XXX, XXX−XXX
Inorganic Chemistry
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complicated because of the existence of two possible diastereomers; see the SI. Dimer M1 = [Zn2(7)2](OTf)4. In 10 mL of CH3CN, 4′-[(4[1,10]phenanthrolin-3-ylethynyl)phenyl][2,2′:6′,2″]terpyridine (7; 3.20 mg, 6.25 μmol) and Zn(OTf)2 (2.27 mg, 6.25 μmol) were refluxed for 2 h. The reaction mixture was then cooled to room temperature and the solvent removed under reduced pressure. The resultant yellow solid was dissolved in CH3OH and filtered, and the filtrate was evaporated to dryness. The residue was redissolved in CD3CN and subjected to analytical characterization without any further purification.52 Yield: ≥60%. Mp: >250 °C. 1H NMR (400 MHz, CD3CN): δ 9.76 (d, 3J = 4.8 Hz, 2 H), 9.07 (d, 3J = 8.4 Hz, 2 H), 8.91 (s, 4 H), 8.70 (d, 3J = 8.0 Hz, 4 H), 8.58 (d, 4J = 2.0 Hz, 2 H), 8.42 (dd, 3J = 8.4 Hz, 3J = 4.8 Hz, 2 H), 8.31 (d, 3J = 9.0 Hz, 2 H), 8.24 (t, 3J = 8.0 Hz, 4 H), 8.15 (d, 3J = 4.8 Hz, 4 H), 8.13 (d, 3J = 9.0 Hz, 6 H), 7.77 (d, 3J = 9.0 Hz, 4 H), 7.55 (dd, 3J = 8.0 Hz, 3J = 4.8 Hz, 4 H), 6.87 (br, 2 H). 13C NMR (100 MHz, CD2Cl2): δ 156.0, 152.3, 150.3, 150.1, 149.7, 148.8, 148.7, 142.8, 142.1, 141.8, 140.6, 139.7, 138.8, 133.5, 131.5, 129.5, 128.2, 127.4, 124.7, 124.5, 123.4, 123.3, 122.2, 120.2, 95.0, 87.5. ESI-MS: m/z 288.3 (35%; [M − 4OTf]4+), 433.7 (65%; [M − 3OTf]3+), 726.4 (100%; [M − 2OTf]2+), 1601.9 (20%; [M − OTf]+). Anal. Calcd for C74H42F12N10O12S4Zn2· CH3CN: C, 50.96; H, 2.53; N, 8.60; S, 7.16. Found: C, 50.78; H, 2.88; N, 8.70; S, 7.19. Protons 2- and 9-H (Scheme 3) are highly diagnostic for the strained structure [Zn2(7)2](OTf)4. While these protons exhibit very similar shifts in 7 (9.33 and 9.22 ppm),44 they are located at 6.87 ppm (2-H) and 9.76 ppm (9-H) in M1. A look at the structure of M1 suggests that proton 2-H should be placed in the shielding zone of the terpyridine because of the strong bending of the ligand. Scalene Triangle T4 = [Zn2Cu(6)(7)(8)](OTf)4(PF6). A mixture of 8 (1.04 mg, 0.776 μmol), 6 (581 μg, 0.776 μmol), 7 (397 μg, 0.776 μmol), [Cu(MeCN)4]PF6 (289 μg, 0.776 μmol), and Zn(OTf)2 (565 μg, 1.55 μmol) was dissolved in acetonitrile and refluxed for 1 h. The solvent was evaporated from the orange solution and the solid subjected to analytical characterization without any further purification. Mp: >250 °C. 1H NMR (600 MHz, CD3CN): δ 9.08 (d, 3J = 8.4 Hz, 1 H), 9.06 (d, 3J = 8.4 Hz, 1 H), 9.06 (s, 1 H), 8.96 (s, 1 H), 8.95 (s, 1 H), 8.86 (d, 3J = 8.4 Hz, 1 H), 8.83 (d, 4J = 1.6 Hz, 1 H), 8.76 (d, 4J = 1.6 Hz, 1 H), 8.68 (dd, 3J = 4.8 Hz, 4J = 1.6 Hz, 1 H), 8.65 (d, 4J = 1.2 Hz, 1 H), 8.63 (d, 4J = 1.2 Hz, 1 H), 8.59−8.57 (m, 2 H), 8.56 (s, 2 H), 8.52−8.48 (m, 4 H), 8.46 (d, 3J = 7.8 Hz, 1 H), 8.39 (d, 3J = 9.0 Hz, 1 H), 8.38 (d, 3J = 9.0 Hz, 1 H), 8.38 (d, 3J = 9.0 Hz, 1 H), 8.34 (d, 3J = 9.0 Hz, 1 H), 8.23 (d, 3J = 8.4 Hz, 2 H), 8.23−8.17 (m, 4 H), 8.15 (d, 3J = 8.4 Hz, 1 H), 8.13 (d, 3J = 8.4 Hz, 1 H), 8.07 (d, 3J = 9.0 Hz, 1 H), 8.04 (d, 3J = 8.4 Hz, 2 H), 8.03 (d, 3J = 9.0 Hz, 1 H), 7.99 (d, 3J = 8.4 Hz, 1 H), 7.96 (d, 3J = 8.4 Hz, 2 H), 7.84 (d, 3J = 8.0 Hz, 3J = 4.8 Hz, 1 H), 7.67 (d, 3J = 5.4 Hz, 1 H), 7.65 (d, 3J = 5.4 Hz, 1 H), 7.60 (d, 3J = 5.4 Hz, 1 H), 7.58 (d, 3J = 5.4 Hz, 1 H), 7.48−7.44 (m, 4 H), 7.43 (d, 3J = 8.4 Hz, 2 H), 6.99 (t, 3J = 8.4 Hz, 1 H), 6.95 (t, 3J = 8.4 Hz, 1 H), 6.64 (t, 3J = 8.4 Hz, 1 H), 6.58 (t, 3J = 8.4 Hz, 1 H), 6.31 (s, 1 H), 6.23 (s, 2 H), 6.17 (d, 3J = 8.4 Hz, 1 H), 6.16 (d, 3J = 8.4 Hz, 1 H), 6.14 (s, 1 H), 6.13 (d, 3J = 8.4 Hz, 2 H), 5.98 (s, 1 H), 5.96−5.94 (m, 2 H), 5.93 (d, 3J = 8.4 Hz, 2 H), 5.87 (d, 3J = 8.4 Hz, 1 H), 3.53 (t, 3J = 6.6 Hz, 2 H), 3.52 (t, 3J = 6.6 Hz, 2 H), 3.00 (s, 3 H), 2.97 (s, 3 H), 2.94 (s, 3 H), 2.91 (s, 3 H), 2.69 (s, 3 H), 2.67 (s, 3 H), 2.65 (s, 6 H), 2.09 (s, 3 H), 1.88 (s, 3 H), 1.79 (s, 3 H), 1.73 (s, 3 H), 1.70 (s, 3 H), 1.61 (s, 3 H), 1.33−1.15 (m, 32 H), 0.80 (t, 3J = 7.2 Hz, 3 H), 3.52 (t, 3J = 7.2 Hz, 3 H). ESI-MS: m/z 558.7 (100%: [M − 4OTf, PF6]5+), 735.6 (55%; [M − 3OTf, PF6]4+), 1030.2 (25%; [M − 2OTf, PF6]3+). Anal. Calcd for C178H152CuF18N14O22PS4Zn2· 3CH2Cl2: C, 57.37; H, 4.20; N, 5.17; S, 3.38. Found: C, 57.37; H, 4.11; N, 4.81; S, 3.34.
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AUTHOR INFORMATION
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[email protected]. ORCID
Michael Schmittel: 0000-0001-8622-2883 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This publication is dedicated to Prof. Dr. Dr. h.c. mult. G. Bringmann on the occasion of his 65th birthday. We are indebted to the Deutsche Forschungsgemeinschaft (Grants 647/15-1 and 20-1) and the University of Siegen for financial support.
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DOI: 10.1021/acs.inorgchem.6b02256 Inorg. Chem. XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.inorgchem.6b02256 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry (58) UV−vis titrations were analyzed by fitting the whole series of spectra at 0.5 nm intervals using the software SPECFIT. The SPECFIT program analyzes equilibrium data sets using singular value decomposition and linear regression modeling by the Levenberg−Marquardt method to determine the cumulative binding constant. (59) Schmittel, M.; Saha, M. L.; Fan, J. Scaffolding a Cage-Like 3D Framework by Coordination and Constitutional Dynamic Chemistry. Org. Lett. 2011, 13, 3916−3919. (60) Liang, Y.; Xie, Y.-X.; Li, J.-H. Modified Palladium-Catalyzed Sonogashira Cross-Coupling Reactions under Copper-, Amine-, and Solvent-Free Conditions. J. Org. Chem. 2006, 71, 379−381.
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DOI: 10.1021/acs.inorgchem.6b02256 Inorg. Chem. XXXX, XXX, XXX−XXX
