Supramolecular RutheniumâAlkynyl Multicomponent Architectures

Article pubs.acs.org/Organometallics

Supramolecular Ruthenium−Alkynyl Multicomponent Architectures: Engineering, Photophysical Properties, and Responsiveness to Nitroaromatics Rafik Gatri,†,‡ Ines Ouerfelli,†,‡ Mohamed Lofti Efrit,† Françoise Serein-Spirau,§ Jean-Pierre Lère-Porte,§ Pierre Valvin,∥ Thierry Roisnel,‡ Sébastien Bivaud,‡ Huriye Akdas-Kilig,‡ and Jean-Luc Fillaut*,‡ †

Laboratoire de Synthèse Organique et Hétérocyclique, Département de Chimie, Faculté des Sciences de Tunis, Campus Universitaire, Université Tunis El Manar 2, 2092 Tunis, Tunisia ‡ Institut des Sciences chimiques de Rennes, UMR 6226 CNRS-Université Rennes 1, Avenue du Général Leclerc, 35042 Rennes cedex, France § AM2N UMR 5253 CNRS-Ecole Nationale de Chimie de Montpellier (ENSCM), 8 rue de l’Ecole Normale, 34296 Montpellier cedex 5, France ∥ Laboratoire Charles Coulomb UMR 5221 CNRS-UM2, Département Semiconducteurs Matériaux et Capteurs, Université Montpellier 2, Place Eugène Bataillon, 34095 Montpellier cedex 5, France S Supporting Information *

ABSTRACT: A series of H-bonded supramolecular architectures were built from monofunctional M−CC−R and bifunctional R−CC−M−CC−R trans-alkynylbis(1,2-bis(diphenylphosphino)ethane)ruthenium(II) complexes and π-conjugated modules containing 2,5-dialkoxy-p-phenylene. Incorporation on each partner of a cyanuric end and of the complementary Hamilton receptor provided the necessary means to keep the constituents together via strong hydrogen bonding. Characterization of all architectures has been performed on the basis of NMR and photophysical methods. In particular, the formation of a Hamilton receptor/cyanuric acid complex has been exemplified by an X-ray single-crystal structure determination. Both self-assembly and accurate modification of the complementary blocks were ensured in such a way that the resulting materials maintain the responsiveness of the electron-rich 2,5-dialkoxy-p-phenylene spacers toward nitroaromatics.

■

INTRODUCTION

based supramolecular assemblies. Together with the versatility of design and the easy access to both monofunctional M−C C−R and bifunctional R−CC−M−CC−R alkynyl(1,2bis(diphenylphosphino)ethane)ruthenium(II) complexes, the linear and rigid arrangement of atoms in the M−CC−R structures makes them viable candidates to generate welldefined and sterically hindered supramolecular architectures,8 as well as for applications in materials chemistry (electron transfer, nonlinear optics, sensing, etc.).9−11 Using conformationally rigid trans-alkynyl ruthenium and π-conjugated organic units containing 2,5-dialkoxy-p-phenylene as molecular modules bearing respectively Hamilton receptor and cyanuric acid complementary units12,13 was expected to result in the preparation of supramolecular architectures. A second part is dedicated to the responsiveness of these architectures in which the fluorescence properties and sensitivity of π-conjugated organic units containing 2,5dialkoxy-p-phenylene to the electron acceptor aromatic ring

The rational design of responsive multicomponent architectures and materials with controlled geometries and properties is key in organic (opto)electronics. In this context, the past decade has witnessed an increasing interest toward supramolecular materials.1−6 The tailoring of supramolecular materials relies on the full control over the self-assembly of molecular modules with complementary recognition sites and dedicated functions, with the expectation that the resulting materials will exhibit distinctive properties and functions.7 Their practical use requires the optimization of their selfassembly and controlled manipulation and the quantitative study of their physicochemical properties and responsiveness to external stimuli. In this paper, we report on the design of multicomponent organometallic based supramolecular architectures, in which 2,5-dialkoxy-p-phenylene containing π-conjugated organic units were incorporated and the evaluation of the optical properties (fluorescence, responsiveness to external stimuli) of the resulting assemblies. A large part of this work was devoted to the design and characterization of the ruthenium acetylide © 2014 American Chemical Society

Received: August 20, 2013 Published: January 29, 2014 665

dx.doi.org/10.1021/om400811z | Organometallics 2014, 33, 665−676

Organometallics

Article

Figure 1. Chemical structures of supramolecular assemblies formed from complexes 3 and 4 and from the conjugated cores 1a (Alk = C8H17), 1b (Alk = C12H25), and 2.

of nitroaromatics14,15 were studied. This study presents an example of how multiple hydrogen bonds could be employed to construct multifunctional architectures, as an alternative way to coordination-driven self-assembly to form tunable supramolecular coordination complexes (SCCs).16−18 Altogether, we demonstrate here that both self-assembly and controlled manipulation of monofunctional M−CC−R and bifunctional R−CC−M−CC−R alkynyl(1,2-bis(diphenylphosphino)ethane)ruthenium(II) complexes and πconjugated organic units containing 2,5-dialkoxy-p-phenylene as complementary blocks can be ensured. In particular, we discuss how the complementary blocks were designed in such a way that the resulting materials exhibit distinctive properties, as for instance fluorescence and responsiveness to nitroaromatics.

for their ability to form an ADAD−DADA pair, via quadruple hydrogen bond formation.8 (1,2-Bis(diphenylphosphino)ethane)ruthenium(II) species were thus chosen as termini, because of the versatility of design. Furthermore, with an overall size of 1.2 nm,25,26 monofunctional M−CC−R and bifunctional R−CC−M−CC−R rigid organometallic units (M = (1,2-bis(diphenylphosphino)ethane)ruthenium(II)) constitute ideal hindered building blocks to create an envelope around the central sensitive units. Applying bifunctional R− CC−M−CC−R units can also provide supramolecular oligomeric species in which the cores containing 2,5-dialkoxy-pphenylene will be inserted through noncovalent bonds. For these reasons, our approach focused on the design of trans-[(dppe)2Ru(X)(CC−R)] bearing one (X= Cl) or two (X = CC−R) Hamilton receptors at the remote end(s) of alkynylruthenium derivatives 3 and 4 (Figure 1). Upon complexation of the Hamilton receptor with cyanuric derivatives, a six-point hydrogen bonding motif is formed that has been proved to be relatively stable at moderate temperature in nonpolar solvents.12,27−31 In furtherance of this design, an important goal concerns the modification of the absorption and emission properties of the 2,5-dialkoxy-p-phenylene cores in these assemblies. Structural modifications of the core were thus investigated to preserve the optical response of the central units to nitroaromatics such as trinitrotoluene (TNT) or its derivative 2,4-dinitrotoluene (DNT) within the assemblies. 1,4-Diethynyl-2,5-dialkoxybenzenes (6a,b) containing πconjugated organic units were first synthesized as central

■

RESULTS AND DISCUSSION Methods. Various approaches by our group and others provided evidence that the accurate design of functional alkynes allows the versatile generation of discrete assemblies of rigidrod transition-metal σ-acetylides, featuring a controlled geometry. For instance, alkynes substituted by nucleobases and by urea-pyrimidinedione constitute valid candidates that allow for the synthesis of transition-metal species capable of acting as supramolecular synthons, both in solution and in the solid state.19−24 In particular, trans-[(dppe)2Ru(Cl)(CC− R)] (dppe = (1,2-bis(diphenylphosphino)ethane)) species bearing terminal bis(acylamino)triazine moieties can be used 666


Organometallics

Article

Scheme 1. Synthesis of 1a,ba

Reagents and conditions: (a) 2.3 equiv of (trimethylsilyl)acetylene (TMSA), 0.02 equiv of PdCl2(PPh3)2, 0.04 equiv of CuI, iPr2NH, THF, 60 °C, 16 h, then NaOH, MeOH, THF, room temperature, 5 h, 6a 85%, 6b 73%; (b) 7, 1 equiv of 4-iodoaniline, H2SO4, HNO3, 0°C, 3 h, 40%; (c) 8, 4.75 equiv of N,N′-carbonyldiimidazole, 5.9 mL of 1 M t-BuOK in THF, THF, 60 °C, 24 h, 77%; (d) 2.2 equiv of 6a or 6b, 9, 0.01 equiv of PdCl2(PPh3)2, 0.02 equiv of CuI, 0.02 equiv of PPh3, NEt3, THF, room temperature, 72 h, 1b 45%. a

temperature for 48 h. 20 was finally obtained as a brown product using a slight excess of potassium fluoride in methanol at ambient temperature and characterized by NMR spectroscopy and mass spectrometry. The reaction of a slight excess (∼1.2 equiv) of [cis(Cl)(PPh2CH2CH2PPh2)2Ru][TfO] and alkyne 20 in dichloromethane at room temperature for 4 days resulted in the formation of an intermediate vinylidene species.33 The reaction was monitored by 31P NMR in order to ensure its completion. This intermediate was clean enough to be used in the next step and was then deprotonated using dry potassium tert-butoxide (room temperature, 16 h). The resulting alkynyl compound was washed with water before being purified by diphasic recrystallization from dichloromethane/pentane (1/2) as a yellow powder in approximately 30% yield. All the spectroscopic data of 3 are consistent with the proposed structure (Scheme 3). 4 was obtained by modifying this procedure: the reaction of 3 equiv of alkyne 20 and [cis-(Cl)(PPh2CH2CH2PPh2)2Ru][TfO] in dichloromethane at room temperature for 2 days resulted in the formation of the same vinylidene species, as monitored by 31P NMR. To this intermediate species were then added successively 3 equiv of both KPF6 and triethylamine. This mixture was stirred at 30 °C for 24 h, to ensure the completion of the reaction as probed by 31P NMR (δ(CDCl3) 54.6 ppm). 4 was washed with water before being purified by diphasic crystallization from dichloromethane/pentane (1/2) as a yellow powder in approximately 50% yield. All products gave

building blocks, to which cyanuric end groups were attached through a Sonogashira coupling, leading to 1a,b (Scheme 1). N(4-Iodophenyl)isocyanuric acid (9) was previously obtained from the reaction of 1-(4-iodophenyl)biuret (8)32 and N,N′carbonyldiimidazole in the presence of potassium tert-butoxide. Long chains (6b) were necessary to ensure that the compounds 1 were sufficiently soluble. 1a was obtained as a yellow solid, hardly soluble in hot THF and DMSO but not soluble enough to allow for purification and characterization. Conversely, 1b was soluble enough to be flash chromatographed on silica gel successively with dichloromethane and tetrahydrofuran as eluents and was further purified by crystallization from hot methanol. In a second step, we synthesized the π-extended analogue 2 in four steps from 1,4-dibromo-2,5-dioctyloxybenzene (5a) (Scheme 2). The preparation of the ruthenium derivatives has been adapted from previously reported procedures (Scheme 3).33 The alkyne 20 was obtained by classical Sonogashira coupling and deprotection procedures from the precursor N,N′-bis[6(3,3-dimethylbutyrylamino)pyridin-2-yl]-5-iodoisophthalamide (19).34 This precursor was obtained from the reaction of 5iodoisophthaloyl dichloride (18) and 2 equiv of N-(6aminopyridin-2-yl)-3,3-dimethylbutyramide (17), in the presence of triethylamine. 20 was achieved by the Sonogashira coupling of 19 with (trimethylsilyl)acetylene (TMSA) in the presence of PdCl2(PPh3)2 and CuI. The reaction was carried out in a 1:1 mixture of THF and diisopropylamine at room 667


Organometallics Scheme 2.

Article

a

Reagents and conditions: (a) 5a (2.00 g; 4.0 mmol), 2.25 equiv of n-BuLi, THF, −78°C, 3 h, then 2.25 equiv of DMF, −78 °C, 1 h, −78 °C to room temperature, 2 h, 34%; (b) 14, 2.2 equiv of (7-bromo-9,9-dioctyl-9H-fluoren-2-yl)methyldiethylphosphonate, 2.6 equiv of t-BuOK, THF, 0 °C to room temperature, overnight, 30%; (c) 15, 2.2 equiv of TMSA, 0.03 equiv of Pd(PPh3)2Cl2, PPh3 (10.0 mg, 0.083 equiv), and 0.03 equiv of CuI, Et3N, THF, reflux, 70 h, then n-Bu4NF (0.9 mL 1 N solution in THF), THF, room temperature, 18 h, 71%; (d) 16, 3 equiv of 9, 0.1 equiv of PdCl2(PPh3)2, 0.16 equiv of CuI, and 0.11 equiv of PPh3, NEt3, room temperature, 4 days, 70%. a

nm. The band positions of UV−vis and fluorescence spectra are thus almost the same for 1b with respect to that of the parent 1,4-bis(phenylethynyl)-2,5-bis(alkoxy)benzene compounds.39 The incorporation of the cyanuric termini does not bring about changes to the electronic structure of the conjugated core, even if a small bathochromic shift (∼5−10 nm) is observed in absorption and emission with respect to 1,4bis(phenylethynyl)-2,5-bis(alkoxy)benzene models. We can also observe that the lowest energy absorption band of 1b is fully overlapped by the MLCT absorption of both 3 and 4, while the absorption spectra of these complexes partially cover the emission of 1b. The absorption and emission spectra of 2 in dichloromethane clearly demonstrate the influence of the styryl substitution and the insertion of fluorene units in the conjugated core (Figure 2). The absorption spectrum shows three main peaks from λ 320 to 370 nm and an intense broad band, its maximum absorption peak being located at 420 nm, which can be attributed to the π−π* transitions within the molecular backbone.40 The bands at higher energy may result from resonant interaction with the oxygen lone pairs.39 The main emission peak appears at 475 nm, with a shoulder peak at 525 nm. The influence of the styryl substitution and the insertion of fluorene units from 1b to 2 is thus reflected by a large red shift of the longest wavelength absorption edge (57

satisfactory proton and 13C NMR and elemental analysis. The 31 P NMR spectra of complexes 3 and 4 show a single sharp singlet, which is consistent with the trans arrangement of the diphosphine ligands around the ruthenium; as expected, these signals appear at δ 49.8 ppm for the mono-alkynyl and δ 54.6 ppm for the bis-alkynyl complexes.8,11,35,36 The electronic absorption spectra of 3 and 4 in dichloromethane solution exhibit intense absorption bands at 250−305 nm and less intense bands at 365 nm (Table 1 and Figure S1 (Supporting Information)). With reference to previous spectroscopic work on monofunctional M−CC−R and bifunctional R−CC−M−CC−R organometallic units (M = (1,2-bis(diphenylphosphino)ethane)ruthenium(II)), the high-energy intense absorption bands are assigned to intraligand (IL) transitions of the diphenylphosphine and alkynyl ligands. The broad bands from 330 to 430 nm which show a hyperchromic shift from 3 to 4 (3, ε = 12050 dm3 mol−1 cm−1; 4, ε = 30525 dm3 mol−1 cm−1) are assigned to dπRu → π*CCR metal-to-ligand charge transfer (MLCT)37,38 transitions. These complexes do not exhibit any luminescence at room temperature. The absorption spectrum of 1b in dichloromethane exhibits two intensity maxima centered around 320 and 375 nm (Figure S2 (Supporting Information)). 1b also exhibits fluorescence emission with a maximum at 418 nm and a shoulder at ∼430 668


Organometallics Scheme 3.

Article

a

Reagents and conditions: (a) 17, 1 equiv of NEt3, 0.5 equiv of 18, THF, 0 °C, 4 h, room temperature, 48 h, 85%; (b) 1.49 mmol of 19, 1.2 equiv of TMSA, 0.015 equiv of PdCl2(PPh3)2, 0.03 equiv of CuI, 0.03 equiv of PPh3, NEt3, THF, room temperature, 48 h, 93%; (c) KF, MeOH, room temperature, 16 h, 93%; (d) [ClRu(dppe)2][TfO], 0.9 equiv of 20, CH2Cl2, room temperature, 4 days, then t-BuOK, CH2Cl2, room temperature, 32%; (e) [ClRu(dppe)2][TfO] (250 mg, 0.23 mmol), 3 equiv of 20, CH2Cl2, 2 days, then 3 equiv of KPF6, 2.3 equiv of NEt3 30 °C, 24 h, 48%. a

Table 1. Photophysical Data for Complexes 3 and 4 and 2,5Dialkoxybenzene Derivatives in Dichloromethane Solution λmax (nm) (ε, L mol−1 cm−1)a

complex 1b 2 3 4

318 350 309 308

(29850), (24650), (32000), (78015),

323 364 360 365

(28760), 377 (26520) (25273), 420 (42000) (12050) (30525)

λem (nm)b 418 475

a

Only the largest absorption maxima are given. bWavelength of emission maximum on excitation at the absorption maximum.

nm; 2715 cm−1) and of the fluorescence spectrum (57 nm; 2871 cm−1), far from the lowest energy absorption bands of the ruthenium complexes 3 and 4. Solution-State 1H NMR Titrations. The association constants of the supramolecular complexes 3·11 and 4·112 (see Scheme 4) were determined by 1H NMR titration experiments. The experiments were performed by the stepwise addition of 50 μL fractions of a 2.0 × 10−2 M solution of 11 to 0.4 mL of a 2.0 × 10−2 M solution of 3 or 1.0 × 10−2 M 4 in CDCl3. The resonances of the NHint and NHext protons can be observed at δ 7.5 and 8.2 ppm as singlets, which is a characteristic of Hamilton receptor derivatives in apolar, non coordinating solvents such as CDCl3.13,41 Dilution studies (50− 100 μM) in CDCl3 revealed weak self-binding for compound 3 at room temperature (Figure S3 (Supporting Information)). A

Figure 2. Absorption (3 × 10−5 M in CH2Cl2) at 298 K and emission (3 × 10−6 M in CH2Cl2; λex 410 nm) spectra of 2. The absorption spectrum of 4 is indicated for comparison.

fit of the chemical shift data for NHext of 3 afforded estimated maximum binding constant Kassoc values of 50 M−1 for dimer 3· 3. Upon complexation of the Hamilton receptor with the cyanuric acid derivative 11, a six-hydrogen bonding motif was expected to be formed. During this process, the NH resonances of the Hamilton receptor underwent a continuous downfield shift until the complete formation of the complexes was 669


Organometallics

Article

Scheme 4. Structures of the Molecules Used for the Self-Assembly NMR Studies of 3, 4, and 11

Figure 3. Self-assembly study between 3 and 11 (0, 0.5, 1.0, 1.5, 2.0, and 3.0 equiv of 11 from bottom to top). Stock solutions were prepared with dissolved 3 (15 mg, 2 × 10−3 mol) and 11 (5.60 mg, 2 × 10−3 mol) in 5 mL of CDCl3. A 0.4 mL portion of the solution of 3 was titrated with 0.05 mL aliquots of the solution of 11. The mixture was kept at room temperature for 1/2 h, in order to ensure the establishment of H-bonding associations.

obtained. After the addition of 0.5 equiv of 11, a broad signal attributed to the NH protons of the cyanuric moiety was observed at δ 13.0 ppm. The resonance of these NH protons underwent a high-field shift and increased broadening in the course of the experiment, due to fast exchange processes between free and bound cyanurate (Figure 3, 3·11; Figure S4 (Supporting Information), 4·112). A Job plot analysis of the titration data was carried out, which confirmed the expected 1:1 (3:11) and 1:2 (4:11)

stoichiometries (Figures S5 and S6 (Supporting Information)). On the basis of these experiments, the association constants Kassoc were determined using a nonlinear curve-fitting procedure.42,43 The calculated values log K1 ≈ 4 (3:11) and log K1K2 ≈ 8.7 (4:11) are in agreement with those reported earlier for cyanuric Hamilton systems.28 The association constants of the complexes 4:11 and 4:112 were thus calculated to be in the same range (log K1 ≈ 4 and log K2 ≈ 4.7). These findings suggest that the two receptor units in 4 almost act 670


Organometallics

Article

by units involved in hydrogen bonding are close to linearity (

Supramolecular RutheniumâAlkynyl Multicomponent Architectures

Recommend Documents

Supramolecular RutheniumâAlkynyl Multicomponent Architectures