AnionâÏ Interactions of Hexaaryl[3]radialenes - American Chemical

Article pubs.acs.org/JPCA

Anion−π Interactions of Hexaaryl[3]radialenes Jack D. Evans,† Courtney A. Hollis,† Sandra Hack,‡ Alexander S. Gentleman,† Peter Hoffmann,‡ Mark A. Buntine,§ and Christopher J. Sumby*,† †

School of Chemistry and Physics, The University of Adelaide, Adelaide, Australia Adelaide Proteomics Centre, The University of Adelaide, Adelaide, Australia § Department of Chemistry, Curtin University, Perth, Australia ‡

S Supporting Information *

ABSTRACT: Coordination polymers and discrete metallosupramolecular assemblies of hexaaryl[3]radialene compounds exhibit intriguing structures with short anion to π-centroid distances in the solid-state. Furthermore, these [3]radialene compounds display useful photophysical and electrochemical properties that make them ideal as potential platforms for anion receptors. In this study, hexafluoro[3]radialene was optimized to the MP2/aug-cc-pVTZ level of theory, and its complexes with halide anions were optimized to HF/6-31G+ +(d,p), MP2/6-31G++(d,p), M06-2X/6-31G++(d,p), and M06-2X/6-311G++(d,p) levels of theory. Hexafluoro[3]radialene was shown to have properties (large positive Qzz and areas of positive electrostatic surface potential) comparable to other compounds that show anion−π interactions. The interaction energies of complexes of hexafluoro[3]radialene with halide anions were calculated and found to be favorable and equivalent to those of fluorinated aromatic compounds. A series of synthetically accessible hexaaryl[3]radialenes were optimized to HF/6-31G++(d,p) theory and their complexes with halides optimized to the M06-2X/6-31G++(d,p) level of theory. The calculated properties of the electron-deficient hexaaryl[3]radialenes also show large positive Qzz quadrupole moments and two areas of positive potential; at the [3]radialene core and the acidic aryl hydrogen atoms. The interaction energies of the complexes of hexaaryl[3]radialenes and halide anions were found to follow the trend F− > Cl− ≈ Br− and correlate with the electron-deficient nature of the [3]radialene. Close contacts were observed between the anion and the radialene core and the aryl hydrogen atoms, suggesting a combination of anion−π and hydrogen bonding is important. Mass spectrometry was used to experimentally observe the complexes of a number of hexaaryl[3]radialenes with F−, Cl−, and Br− predicted computationally. Anion−[3]radialene complexes were successfully detected, and the stability of the complexes in tandem MS/MS experiments was found to support the computational results.

■

Radialenes are a class of compounds defined by cyclic sp2hybridized ring atoms and exocyclic carbon−carbon double bonds; Figure 1a.22,23 The [3]radialene core is the most easily accessible of these systems obtained through the facile syntheses of hexaaryl[3]radialenes; see Figure 1c.24−28 These compounds are significantly electron-deficient, undergoing two stepwise reductions producing the radical anion and the dianion.28 Furthermore, hexaaryl[3]radialenes have strong fluorescence and absorbance, attractive properties for a functional anion sensor.26,28 A recent perspective article has discussed the prevalence of anion−π interactions in crystal structures with a detailed search of the Cambridge Structural Database revealing that real examples of these interactions are extremely rare.29 On the basis of these observations, it was proposed, by Hay,29 that real examples of solid-state anion−π interactions should fulfill the following guiding principles: (a) exhibit a geometry corre-

INTRODUCTION

Anions are present throughout all biological systems and often play important roles in medicine and catalysis.1−3 DNA, which is a polyanion, and more than two-thirds of enzyme substrates and cofactors are anionic.1−3 In the design and development of anion receptors, many intermolecular forces are employed. Frequently, a combination of electrostatic attraction, Lewis acid moieties, and hydrogen bonding motifs are used.3−11 In addition to these commonly utilized and well-studied interactions, electron-deficient π-systems with positive quadrupole moments have been reported to attract anions.12−14 These interactions, named anion−π, are defined by electrostatic attraction and anion-induced polarization of the π-system.13,15−17 There have been a number of examples of this interaction observed in the gas phase,18 solid-state,15−17,19 and in solution.20 In addition, the functional relevance of anion−π interactions have been demonstrated in the production of synthetic chloride channels.21 Thus, the use of anion−π interactions may aid in the production of strong and selective anion receptors. © 2012 American Chemical Society

Received: February 13, 2012 Revised: June 5, 2012 Published: June 29, 2012 8001

dx.doi.org/10.1021/jp301464s | J. Phys. Chem. A 2012, 116, 8001−8007

The Journal of Physical Chemistry A

■

Article

EXPERIMENTAL METHODS

Theoretical Methods. Optimization, frequency, and quadrupole moment calculations were performed using the Gaussian09 suite of programs.34 Hexafluoro[3]radialene was optimized using to the MP2/aug-cc-pVTZ level of theory with no imaginary frequencies present. The hexafluoro[3]radialene− halide complexes were optimized at the HF/6-31G++(d,p), M06-2X/6-31G++(d,p), MP2/6-31G++(d,p), and M06-2X/6311G++(d,p) levels of theory to produce structures with zero imaginary frequencies. The highest symmetry of C3v was attained for all but two optimizations (1-F and 1-Cl M06-2X/631 g++(d,p) result in C3 symmetry), by using loose symmetric constraints (keyword, symm=loose). A comparison of these geometries, displayed in Table 1, show that each of the methods describes a similar trend in interaction energy and displacements. The M06-2X functional has been previously reported to describe anion−π interactions reliably.35 The resulting energies and displacements of 1-halide complexes produced using M06-2X, in this study, correlate well with RIMP2/aug-pVTZ results of Deyá and co-workers.36 Halide complexes of 4, 5, 6 and 7 were optimized to the M06-2X/6-31++G(d,p) theory with loose symmetry constraints. Frequency calculations were unable to be completed due to the complexity of the structures. All binding energies were calculated with corrections for basis set substitution error (BSSE) using the counterpoise method, as performed in previous studies.12,36,37 Electrostatic potential surfaces (ESP) were produced by mapping the electrostatic potential onto the electron density surface at a density of 0.005 e·Å−3. Molecular orbitals were also produced at an isovalue of 0.02 a.u. using Gaussview. Mass Spectrometry. All high-resolution mass data were measured with an LTQ Orbitrap XL ETD hybrid mass spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) equipped with an ESI source. Samples were infused at 5 uL min−1 using the built-in syringe pump and a spraying voltage of −2.3 kV. A mass resolution of 30,000 (at m/z 700) was used. MS/MS experiments were performed in the ion trap with an isolation width of 5 m/z. Stability of the complexes were measured by comparing the normalized collision energy (NCE) required to diminish the complex to an intensity signal less than 50% of the initial intensity. Solutions of 5, 6, and 7 were prepared with (nBu)4NX (X = F, Cl, Br) in a 1:100 molar ratio.

Figure 1. (a) Parent [3], [4], [5], and [6]radialenes; (b) examples of fluorinated derivatives (1−3) used to probe anion−π interactions; and (c) synthetically accessible hexaaryl[3]radialenes (4−7).

sponding to electronic structure calculations; (b) have the anion located above the core centroid; and (c) involve a charge neutral compound. A number of coordination complexes of hexaaryl[3]radialenes have been reported that show close contacts between anions and the [3]radialene core.30−33 However, despite the packing of these compounds and anions within the crystal lattice, the simple observation of close contacts alone may not definitively identify these as examples of anion−π interactions.29 Herein, we examine this interaction for hexaaryl[3]radialenes and investigate whether hexaaryl[3]radialenes show measurable interactions between anions and the [3]radialene core; in particular, we attempt to discern whether anion−π interactions are responsible for the short contacts observed in previous solid-state structures. Furthermore, we seek to understand the role of weak hydrogen bonding, particularly involving the acidic hydrogen atoms of the hexaaryl[3]radialene, in such contacts. We report calculated properties and halide interactions of hexafluoro[3]radialene 1 and a series of increasingly electrondeficient, synthetically accessible hexaaryl[3]radialenes 4−7. Furthermore, mass spectrometry experiments were undertaken to validate the predicted trends in the gas phase.

■

RESULTS AND DISCUSSION [3]Radialene−Anion Interactions. The properties of hexafluoro[3]radialene, 1, were considered to determine the practicality of the electron-deficient [3]radialene core in anion−π interactions. The values of the quadrupole moment and molecular polarizability were calculated. A comparison of the Qzz quadrupole moment and molecular polarizability

Table 1. Comparison of Interaction Energies (Ei, kJ·mol−1) and Equilibrium Distances between the Anion and the [3]Radialene Centroid (Re, Å) for the Halide Complexes of [3]Radialene 1 with Differing Levels of Theory HF/6-31++G(d,p)

M06-2X/6-31++G(d,p) (M06-2X/6-311+G(d,p))

MP2/6-31G++(d,p)

complex

Ei

Re

Ei

Re

Ei

Re

1 + F− 1 + Cl‑− 1 + Br−

−56.0 −30.4 −26.1

2.654 3.532 3.764

−65.5 −41.5 −40.88

2.519 3.334 3.476

−80.4 (−82.8) −48.2 (−47.8) −44.5 (−43.5)

2.405 (2.440) 3.181 (3.181) 3.380 (3.380)

8002



Article

orthogonal to the plane of the molecule, α∥, of 1 and other perfluorinated-cyclic compounds are shown in Table 2.

characterized.24−28 To determine the propensity of these compounds to form anion interactions, their properties were analyzed. The calculated Qzz quadrupole moments and electrostatic potential energy surfaces were compared to the reduction potentials of the radialenes (Table 3).

Table 2. Quadrupole Moments (Qzz, B), Molecular Polarizabilities Orthogonal to the Molecular Plane (α∥, a.u.) for Compounds 1−3, and Interaction Energies (Ei, kJ·mol−1) and Equilibrium Distances between the Anion and the Ring Centroid (Re, Å) for Halide Anion Complexes of 1−3 compd

Qzz

α∥

1

5.15a

37.1a

2

9.50c

37.7d

3

3.35d

37.7d

complex 1 1 1 2 2 3 3

+ + + + + + +

F− Cl− Br− Cl− Br− Cl− Br−

Ei

Re

−82.8a −47.8a (−46.7)b −43.5a (-43.0)b −53.4e (−62.1)b −51.0e (−57.3)b −33.8e −32.2e

2.44a 3.18a (3.13)b 3.38a (3.32)b 3.16e (3.07)b 3.23e (3.24)b 3.25e 3.31e

Table 3. Quadrupole Moments (Qzz, B), Maximum Electrostatic Potential Values at the [3]Radialene Core and the Aryl Hydrogen Atoms (ESP, kJ·mol−1), and Reduction Potentials (Ered, V)28 of Hexaaryl[3]radialenes 4−7 compd

Qzz

ESP[3]radialene

ESPhydrogens

Ered(1)

Ered(2)

4 5 6 7

−7 53 105 140

91.9 229 238 342

176 306 310 410

−0.80 −0.63 −0.06

−1.32 −1.03 −0.45

The Qzz quadrupole moment of 4, lacking electron withdrawing substituents, was found to be negative and not conducive to the formation of anion−π interactions. The addition of nitrile groups in the meta and para positions produces more electron-deficient compounds reflected by their lower reduction potentials. As the electron density of the core and aryl groups is withdrawn by the nitrile substituents, it is unsurprising that the Qzz quadrupole moments are observed to be large and positive. The effects of having nitrile groups in the para and meta positions on the Qzz quadrupole moment are observed to be approximately cumulative for the most electrondeficient compound, 7. The electrostatic potential surfaces of the more electrondeficient derivatives 5, 6, and 7, Figure 3, show two areas of

a

From this study, computed at the M06-2X/6-311++G(d,p) level. Computed at the RI-MP2/aug-cc-pVTZ level, taken from ref 36. c Taken from ref 38. dThese values were extracted or calculated from geometries given in ref 12. eComputed at the MP2/6-31++G(d,p) level, taken from reference 12. b

The [3]radialene core has a similar polarizability to that of 2, a molecule that displays explicit anion−π interactions.19 Although the quadrupole moment is not as large as that of its structural isomer, 2, it is larger than other cyclic compounds such as 3. The electrostatic potential surface (ESP) of 1, presented in Figure 2a, shows that the exocyclic double bonds

Figure 2. (a) Electrostatic potential surface of 1 (blue positive, red negative) and (b) the structure of the chloride complex of 1.

have localized areas of positive potential, which are required for anion interactions to occur, although these are not localized over the cyclopropane ring of 1. Instead, the positive potential is localized on the exocyclic carbons due to the electron withdrawing nature of the fluorine substituents and the lack of aromaticity of the [3]radialene system. Thus, the properties of 1 suggest that hexaaryl[3]radialenes may show favorable anion−π interactions. The dependence on anion size observed for the interaction energy is similar to other anion−π interactions. The geometry of the M06-2X optimized complexes, in Figure 2b, show the anion on the C3 axis, analogous to reported geometries of anion−π complexes of 2.12,35 These results show that the electron-deficient [3]radialene π-system is a favorable environment for anion−π interactions that may be used in conjunction with other interactions to design potential anion receptors. Hexaaryl[3]radialene−Anion Interactions. The hexaaryl[3]radialenes studied in this investigation are shown in Figure 1c. The structures of these compounds vary with the addition and different substitution patterns of nitrile groups onto the phenyl rings to produce increasingly electron-deficient derivatives. These have been previously synthesized and

Figure 3. Electrostatic potential surfaces (blue positive, red negative) of compounds 4−7.

localized positive potential where anions may be attracted, the aryl hydrogens and [3]radialene core. The maximum values of ESP, Table 3, show that the aryl hydrogens are acidic and exhibit greater positive potential. With the addition of electron withdrawing groups, in 5, 6, and 7, there are areas of negative potential at the nitrile nitrogen atoms consistent with having a greater electron density than carbon atoms. The core in 5 shows a significantly different ESP to that of 4. The addition of 8003



Article

the dipole moment of the molecule. However, the alternating conformation, 5a, possesses greater energetic stability than 5b and thus will be more prevalent. Conformer 5a also exhibits a much larger quadrupole moment; therefore, we decided to use this conformation of 5 and 7 as the basis of the model on which anion−π interactions were investigated. Compounds 4 and 6 lack dipole moments, and as such, this effect was not required to be considered across the entire series. The hexaaryl[3]radialenes 4−7 were optimized with a series of halide anions, F−, Cl−, and Br−, using M06-2X/6-31+ +G(d,p), yielding a geometry where the anion is localized above the [3]radialene core on the C3 axis. The geometries obtained display weak hydrogen bonding as shown by close contacts between the anion and three aryl hydrogens. The anions are also observed to be in close proximity with the center of the [3]radialene. There is a noticeable angle of flex of the exocyclic double bonds toward the anion when bound with fluoride. This flex is enhanced in electron-deficient [3]radialenes and is a consequence of the attraction between the anion and proximal hydrogen atoms. It was recognized that systems with the greatest flex exhibit the smallest distance between the anion and the proximal hydrogen atoms producing an improved interaction. The interaction energies and anion displacements of the complexes are summarized in Table 5. For comparison, the halide complexes were optimized using the HF/6-31++G(d,p) theory; see Supporting Information, Table S1.

electron withdrawing groups produces a large increase in positive potential at the center of the radialene core. This observation is consistent for 6 and 7. The variance in ESP surfaces for the series shows an increase in intensity of this localized positive potential at the core as the molecule becomes more electron-deficient. Thus, the ESP surface measurements identify two complementary regions within compounds 5, 6, and 7 amenable to anion binding. In this study, compounds 5 and 7 have a number of possible conformers owing to free rotation of the phenyl substituents. The conformers of the aligned and alternating geometry of 5, shown in Figure 4, were considered. Analysis of the energies of

Figure 4. Structures of the alternating (5a) and aligned (5b) conformers of 5.

the optimized structures reveals that the minimum energy configuration corresponds to the alternating structure, 5a. The difference in energy between the two conformers is 10.5 kJ·mol−1, which is consistent with there being free rotation on the NMR time scale in the solution structures of these compounds at room temperature. The electronic properties of the alternating conformer, 5a, and aligned conformer, 5b, and their complexes are displayed in Table 4. As a consequence of alignment of the local dipole

Table 5. Interaction Energies (Ei, kJ·mol−1), Equilibrium Distances between the Anion and the [3]Radialene Centroid (R[3]radialene, Å), and Equilibrium Distances between the Anion and Proximal Aryl Hydrogen Atoms (RH, Å) for Halide Complexes of Compounds 4−7 compd −

4-F 4-Cl− 4-Br− 5-F− 5-Cl− 5-Br− 6-F− 6-Cl− 6-Br− 7-F− 7-Cl− 7-Br−

Table 4. Comparison of Dipole Moment Orthogonal to the Molecular Plane (D, D), Quadrupole Moment (Qzz, B), Interaction Energy (Ei, kJ·mol−1), and Equilibrium Distances between Anion and [3]Radialene Centroid (R[3]radialene, Å) in Fluoride Complexes of the Conformers 5a and 5b compd

D

Qzz

Ei

R[3]radialene

5a 5b

0 −18

54 13

−249 −232

2.745 2.694

moment of the nitrile groups, conformer 5b develops a molecular dipole moment perpendicular to the radialene plane. Furthermore, upon alignment of the nitrile groups, the quadrupole moment decreases by a large amount. In the case of alternating nitrile groups (5a), there is no dipole calculated as the individual dipole moments of each of the nitrile groups cancel. The alternating geometry has a great effect on the quadrupole moment of the radialene, however. As anion−π interactions have been shown to be dependent on this property, the alternating conformer, with its large Qzz, has the greatest propensity to form anion−π interactions. The interaction of fluoride with each of the conformers was modeled. The interaction energies and anion displacements for the alternating complex and the aligned complex, when the fluoride is aligned with the dipole moment, are shown in Table 4. The interaction energy of the fluoride complex for the aligned conformer 5b is more favorable due to interaction with

R[3]radialene

RH

Ei

2.709 3.354 3.498 2.632 3.217 3.374 2.637 3.222 3.303 2.600 3.171 3.295

2.018 2.592 2.794 1.948 2.499 2.702 1.955 2.506 2.614 1.902 2.465 2.665

−148 −79.0 −67.1 −249 −190 −174 −279 −192 −176 −354 −279 −259

There are a number of trends that can be identified upon inspection of the results. First, 4, with no electron withdrawing groups, is found to have a favorable interaction with the anions through weak hydrogen bonding. This is evident as the anion displacement from the [3]radialene core of 4 is independent of the anion radius. With the addition of electron-withdrawing substituents, the interaction becomes increasingly favorable. This result is not unsurprising as the aryl hydrogen atoms become more acidic along with the increased electron deficiency of the [3]radialene core. The interaction is shown to decrease considerably with larger anions like bromide. The dependence on the charge density of the anions corresponds to the electrostatic nature of the interaction.37 For the electrondeficient compounds, 5−7, there is a clear relationship between the interaction energies and the halide distance from the 8004



Article

an antibonding distribution. Because of the increased size of the anion and crowding of the radialene core, it is unsurprising that the orbitals cannot align like for fluoride. The lower interaction energy for the chloride and bromide complexes is explained by this effect. Investigations by Mass Spectrometry. Negative ion high-resolution mass spectrometry (HR-MS) was used to validate the computational results. Mass spectrometry has an advantage over nuclear magnetic resonance spectroscopy in the study of weak noncovalent interactions,40−45 like those predicted here, due to the elimination of solvent effects. Solutions of hexaaryl[3]radialene 5, 6, and 7 were prepared with anion salts of fluoride, chloride, and bromide. The solvent was chosen carefully, as the compounds are soluble in methanol and other protic solvents, which could competitively interact with the anions causing difficulty in desolvation. In order to prevent this, acetonitrile was chosen, as it is aprotic and also provides solubility for all components. Complexes of 5, 6, and 7 with each of the halides were detected in the gas phase, mass selected, and further examined. The overlaid fragmentation spectrum featuring complexes of 6 and 7 is shown in Figure 6. The fragmentation of each of the

[3]radialene core. The distances observed computationally are also corroborated by distances observed in solid-state structures of [3]radialenes; a [Ag6F(L)2]5+ complex31 (where L = hexakis(2-pyridyl)[3]radialene) has a fluoride-[3]radialene centroid distance of 2.72(1) Å that is very similar to the values obtained by computational approaches. The energies and geometries of the complexes reveal that these complexes are likely to be stabilized by a combination of an anion−π interaction with the radialene core and hydrogen bonding interactions with the proximal aryl hydrogens. This observation of a combined interaction is supported by the meta (5) and para (6) substituted hexaaryl[3]radialenes possessing similar binding energies. Although their electron withdrawing properties dictate that the para-substituted derivative 6 should bind halides more strongly, in 5, nitrile groups withdraw electron density from the ortho and para positions making the hydrogen atoms in these positions more acidic. Increased acidity results in an improved hydrogen bonding interaction, which accounts for the enhanced anion binding of 5 as the proximal aryl hydrogens are ortho and para to the nitrile groups, in contrast to 6, where the proximal hydrogens are meta to nitrile groups. To further understand the interaction, the valence molecular orbitals were studied, a number of which are displayed in Figure 5. For the fluoride complexes, the HOMOs include two

Figure 6. Overlaid MS/MS spectrum of the fragmentation of halide complexes for 6 and 7.

complexes is observed to produce the deprotonated molecular ion resulting from the complex expelling the acid form of the halide conjugate base. The stability of the complexes were probed through comparison of the signal intensities for a particular ion with increasing normalized collision energy (NCE) relative to the signal intensities that are observed with an NCE of zero. Comparison of NCE values, although qualitative, has been used to infer the stability of other complexes.46 As expected, it was observed that the complexes fragment at a much lower NCE value than the ion of the initial hexaaryl[3]radialene owing to the weaker noncovalent forces involved. Comparison of the series47 revealed that the complex stability follows a trend with anions where F− > Cl− ≈ Br−. Because of the lack of resolution in incremental increases of the NCE, the difference between the chloride and bromide complex stability was unable to be discerned. The signal intensity of the initially formed fluoride complexes was observed to be much smaller than the other halide complexes. This is expected because of the difficulties associated with the desolvation of fluoride.48 In contrast, chloride complexes were easily detected due to the ubiquity of chloride and its relative ease of desolvation. Distinguishing a trend in stability for the different hexaaryl[3]radialenes also proved difficult. However, the fluoride complexes of compound 7 were significantly more

Figure 5. Surface plot of valence molecular orbitals of hexaaryl[3]radialene halide complexes.

degenerate molecular orbitals. The molecular orbitals shown contain π-type orbitals distributed on the radialene and a localized p-type orbital on the fluoride anion. The p-type anion orbitals are observed to associate with the radialene orbitals in a similar manner to that of anion−π interactions shown by Deyá and co-workers.39 The degenerate HOMOs display an antibonding contribution of molecular orbitals of the radialene and anion. As a result of this, the HOMOs represent an electron−electron repulsion that repolarizes the π-electrons of the radialene producing a stabilizing interaction; thus, the polarization effect is observed in these complexes.39 The HOMO orbitals for the chloride and bromide complexes were found to have a different distribution as there is a single nondegenerate HOMO that contains nonbonding p-type orbitals found predominately on the anion. The orbital is orientated toward the radialene core and a small amount of density is observed on the radialene core carbon atoms forming 8005



Article

through a Discovery Project (DP0773011). We thank eResearch SA for access to high performance computing facilities.

stable than those of compounds 5 and 6. Similarity in stability for complexes of 5 and 6 was also observed, and this is expected due to an amount of conformer 5b present in the population that may bind through stronger dipole interactions. In summary, mass spectrometry experiments were able to show physical evidence for the complexes, in solutions of the radialenes and halide salts, predicted by the initial calculations. The stability of the complexes followed the predicted trends.

■

(1) Bauduin, P.; Renoncourt, A.; Touraud, D.; Kunz, W.; Ninham, B. W. Curr. Opin. Colloid Interface Sci. 2004, 9, 43−47. (2) Meyer, E. A.; Castellano, R. K.; Diederich, F. Angew. Chem., Int. Ed. 2003, 42, 1210−1250. (3) Bianchi, A.; Bowman-James, K.; Garcia-Espana, E., Eds. Supramolecular Chemistry of Anions; Wiley-VCH: New York, 1997. (4) Schmidtchen, F. P.; Berger, M. Chem. Rev. 1997, 97, 1609−1649. (5) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486−516. (6) Schmidtchen, F. P. Top. Curr. Chem. 2005, 255, 1−30. (7) Gale, P. A. Chem. Soc. Rev. 2010, 39, 3746−3771. (8) Ballester, P. Chem. Soc. Rev. 2010, 39, 3810−3830. (9) Li, A.-F.; Wang, J.-H.; Wang, F.; Jiang, Y.-B. Chem. Soc. Rev. 2010, 39, 3729−3745. (10) Cavallo, G.; Metrangolo, P.; Pilati, T.; Resnati, G.; Sansotera, M.; Terraneo, G. Chem. Soc. Rev. 2010, 39, 3772−3783. (11) Gale, P. A. Chem. Commun. 2011, 47, 82−86. (12) Alkorta, I.; Rozas, I.; Elguero, J. J. Am. Chem. Soc. 2002, 124, 8593−8598. (13) Ballester, P. Struct. Bonding 2008, 129, 127−174. (14) Robertazzi, A.; Krull, F.; Knapp, E.-W.; Gamez, P. CrystEngComm 2011, 13, 3293−3300. (15) Schottel, B. L.; Chifotides, H. T.; Dunbar, K. R. Chem. Soc. Rev. 2008, 37, 68−83. (16) Hay, B. P.; Bryantsev, V. S. Chem. Commun. 2008, 2417−2428. (17) Frontera, A.; Gamez, P.; Mascal, M.; Mooibroek, T. J.; Reedijk, J. Angew. Chem., Int. Ed. 2011, 50, 9564−9583. (18) Mascal, M.; Armstrong, A.; Bartberger, M. D. J. Am. Chem. Soc. 2002, 124, 6274−6276. (19) Quiñonero, D.; Garau, C.; Rotger, C.; Frontera, A.; Ballester, P.; Costa, A.; Deyà, P. M. Angew. Chem., Int. Ed. 2002, 41, 3389−3392. (20) Berryman, O. B.; Hof, F.; Hynes, M. J.; Johnson, D. W. Chem. Commun. 2006, 506−508. (21) Dawson, R. E.; Hennig, A.; Weimann, D. P.; Emery, D.; Ravikumar, V.; Montenegro, J.; Takeuchi, T.; Gabutti, S.; Mayor, M.; Mareda, J.; Schalley, C. A.; Matile, S. Nat. Chem. 2010, 2, 533−538. (22) Hopf, H.; Maas, G. Angew. Chem., Int. Ed. 1992, 31, 931−954. (23) Gholami, M.; Tykwinski, R. R. Chem. Rev. 2006, 106, 4997− 5027. (24) Fukunaga, T. J. Am. Chem. Soc. 1976, 98, 610−611. (25) Enomoto, T.; Kawase, T.; Kurata, H.; Oda, M. Tetrahedron Lett. 1997, 38, 2693−2696. (26) Enomoto, T.; Nishigaki, N.; Kurata, H.; Kawase, T.; Oda, M. Bull. Chem. Soc. Jpn. 2000, 73, 2109−2114. (27) Matsumoto, K.; Harada, Y.; Kawase, T.; Oda, M. Chem. Commun. 2002, 324−325. (28) Avellaneda, A.; Hollis, C. A.; He, X.; Sumby, C. J. Beilstein J. Org. Chem. 2012, 8, 71−80. (29) Hay, B. P.; Custelcean, R. Cryst. Growth Des. 2009, 9, 2539− 2545. (30) Hollis, C. A.; Hanton, L. R.; Morris, J. C.; Sumby, C. J. Cryst. Growth Des. 2009, 9, 2911−2916. (31) Steel, P. J.; Sumby, C. J. Chem. Commun. 2002, 322−323. (32) Steel, P. J.; Sumby, C. J. Inorg. Chem. Commun. 2002, 5, 323− 327. (33) Matsumoto, K.; Harada, Y.; Yamada, N.; Kurata, H.; Kawase, T.; Oda, M. Cryst. Growth Des. 2006, 6, 1083−1085. (34) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; et al. Gaussian 09, revision A.02; Gaussian Inc.: Wallingford CT, 2009. (35) Wheeler, S. E.; Houk, K. N. J. Phys. Chem. A 2010, 114, 8658− 8664.

■

CONCLUSIONS In summary, the anion−π interactions of the electron-deficient [3]radialene motif have been studied through the analysis of the properties and interactions of the model compound 1 and the increasingly electron-deficient hexaaryl[3]radialenes 4−7. The truncated model 1 was shown to have properties that support anion−π interactions, a high polarizability and quadrupole moment, which compare well with previously reported aromatic compounds that exhibit strong anion−π interactions. The complexes optimized in this study confirm that the properties of [3]radialenes result in good interactions with anions. The properties of a series of hexaaryl[3]radialenes 4−7 that have shown anion−π interactions in the solid-state were found to have extremely large quadrupole moments. Furthermore, these compounds have areas of positive potential at the [3]radialene core, in addition to acidic aryl hydrogens, which have the potential to form interactions with anions. The series of increasingly electron-deficient hexaaryl[3]radialenes were found to interact well with the halides F−, Cl−, and Br−. The interaction was shown to be dependent on the displacement from the radialene center and proximal aryl hydrogens. The more electron-deficient compounds produce stronger interactions due to stronger anion−hydrogen bonds and anion−π effects. The complexes studied computationally were observed in the gas phase through tandem MS/MS experiments. The interaction between radialenes 5−7 and the halides F−, Cl−, and Br− were examined, and the stability of the complexes are in good agreement with the computational results. In conclusion, this study has successfully shown the applicability of the [3]radialene motif in hexaaryl[3]radialenes for anion binding through a combination of anion−π interactions and hydrogen bonding.

■

ASSOCIATED CONTENT

S Supporting Information *

Interaction energies and displacements for hexaaryl[3]radialene complexes computed at the HF/6-31G++(d,p) theory, full details on the MS/MS experiments for compounds 5−7 showing NCE values for each species, and the complete details of ref 34. This material is available free of charge via the Internet at http://pubs.acs.org.

■

REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Phone: +61 8 8303 7406. Fax: +61 8 8303 4358. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS C.J.S. thanks the Australian Research Council (ARC) for a Future Fellowship (FT0991910) and supporting this research 8006



Article

(36) Estarellas, C.; Frontera, A.; Quiñonero, D.; Deyá, P. M. J. Phys. Chem. A 2011, 115, 7849−7857. (37) Quiñonero, D.; Garau, C.; Frontera, A.; Ballester, P.; Costa, A.; Deyà, P. M. J. Phys. Chem. A 2005, 109, 4632−4637. (38) Williams, J. H. Acc. Chem. Res. 1993, 26, 593−598. (39) Garau, C.; Frontera, A.; Quiñonero, D.; Ballester, P.; Costa, A.; Deyá, P. M. Chem. Phys. Lett. 2004, 399, 220−225. (40) Sansone, F.; Chierici, E.; Casnati, E.; Casnati, A.; Ungaro, R. Org. Biomol. Chem. 2003, 1802−1809. (41) Kavallieratos, K.; Sabucedo, A. J.; Pau, A. T.; Rodriguez, J. N. J. Am. Soc. Mass Spectrom. 2005, 1377−1383. (42) Draper, W. M.; Behnival, P.; Wijekoon, D. Rapid Commun. Mass. Spectrom. 2008, 2613−2620. (43) Becherer, T.; Meshcheryakov, D.; Springer, A.; Bohmer, V.; Schalley, C. Am. J. Mass Spectrom. 2009, 1338−1347. (44) Utley, B.; Angel, L. A. Eur. J. Mass Spectrom. 2010, 16, 631−643. (45) Révész, A.; Schröder, D.; Svec, J.; Wimmerová, M.; Sindelar, V. J. Phys. Chem. A 2011, 115, 11378−11386. (46) Huffman, C. L.; Williams, M. L.; Benoist, D. M.; Overstreet, R. E.; Jellen-McCullough, E. E. Rapid Commun. Mass Spectrom. 2011, 25, 2299−2309. (47) See Supporting Information. (48) Barnett, D. A.; Horlick, G. J. Anal. At. Spectrom. 1997, 12, 497− 501.

8007


AnionâÏ Interactions of Hexaaryl[3]radialenes - American Chemical

Recommend Documents

AnionâÏ Interactions of Hexaaryl[3]radialenes - American Chemical