Efficient Loading and Kinetic Trapping of Hexameric Pyrogallolarene Capsules in Solution

Kvasnica, Miroslav; Chapin, Jennifer C.; Purse, Byron W.

doi:10.1002/ange.201007800

Cited by 10 publications

(2 citation statements)

References 34 publications

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“…Cationic species experience attractive interactions with the electron rich and shallow bowls of the resorcinarene units. [17][18][19] Furthermore, the inner volume of the capsule is large (1375 Å 3 ) and can a priori simultaneously accommodate standard monomeric cationic gold catalysts and their respective substrates. [17][18][19] Furthermore, the inner volume of the capsule is large (1375 Å 3 ) and can a priori simultaneously accommodate standard monomeric cationic gold catalysts and their respective substrates.…”

Section: Resultsmentioning

confidence: 99%

“…Thus, they tend to be included within the closed aromatic cavity provided by hexameric assembly 3 6 ·8H 2 O (which, for simplicity, will herein be referred to as 3 6 ). [17][18][19] Furthermore, the inner volume of the capsule is large (1375 Å 3 ) and can a priori simultaneously accommodate standard monomeric cationic gold catalysts and their respective substrates. The encapsulation of cationic gold catalysts related to [1-tmbn] + (tmbn = 2,4,6-trimethoxybenzonitrile) within the resorcinarene hexamer 3 6 was previously described in the above-mentioned study by Reek, Scarso et al [8] By using a similar encapsulation technique to that reported by Reek, Scarso and co-workers, [8] we mixed the SbF 6 salt of complex [1-tmbn] + and resorcinarene 3 in a 1:10 molar ratio in water-saturated CDCl 3 .…”

Section: Resultsmentioning

confidence: 99%

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Encapsulation Studies of Cationic Gold Complexes within a Self‐Assembled Hexameric Resorcin[4]arene Capsule

et al. 2013

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As the field of supramolecular catalysis develops, a sound fundamental understanding of the catalytic assemblies used will be essential. There is a lack of knowledge regarding systems based on transition‐metal catalysts as guests of supramolecular capsules. We investigate the inclusion behavior of gold complexes based on well‐known cationic Au(I) catalysts within a self‐assembled hexameric resorcin[4]arene capsule. The results shed light on the nature of the encapsulated species and the way in which those species are encapsulated. We introduce an encapsulation methodology that functions through the transient introduction of an excess of water. Through small modifications in the encapsulation methodology, we show that the inclusion process can be controlled to give different encapsulated species stemming from the same gold(I) precursor.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Encapsulation Studies of Cationic Gold Complexes within a Self‐Assembled Hexameric Resorcin[4]arene Capsule

et al. 2013

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Hexameric Capsules Studied by Magic Angle Spinning Solid‐State NMR Spectroscopy: Identifying Solvent Molecules in Pyrogallol[4]arene Capsules

2015

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Powders of pyrogallol [4]arene hexamers were produced by evaporation from organic solvents and were studied, for the first time,b ym agic angle spinning solid-state NMR (MAS ssNMR). Evaporation selectively removed nonencapsulated solvent molecules leaving stable hexameric capsules encapsulating solvent molecules.A fter exposure of the powder to solvent vapors, 1 H/ 13Cheteronuclear correlation MAS ssNMR experiments were used to assign the signals of the external and encapsulated solvent molecules.T he formed capsules were stable for months and the process of solvent encapsulation was reversible.According to the ssNMR experiments,t he encapsulated solvent molecules occupyd ifferent sites and those sites differ in their mobility.T he presented approach paves the way for studying guest exchange,g uest affinity,a nd gas storage in hexamers of this type in the solid state.Self-assembled molecular capsules have attracted much interest over the past two decades. [1,2] Their importance stems, inter alia, from their ability to serve as nanoreactors where new chemistry and catalysis may emerge.O ne intriguing family of self-assembled molecular capsules is resorcin-[4]arenes and pyrogallol[4]arenes hexamers (1 and 2, Figure 1), [3][4][5][6][7] which have been found to be more abundant than previously thought. [8a,b] Resorcin[4]arene hexamers accommodate amuch larger range of guests than pyrogallol-[4]arene hexamers do [8] and several examples of catalysis within the resorcin[4]arene hexamers have been reported. [9] To partially overcome the limited range of guests that can be encapsulated in organic solutions of pyrogallol[4]arene hexamers,Purse and co-workers employed the melting approach; however, this approach is applicable only in certain cases. [10] Thei nformation gathered to date on the hexameric capsules of systems 1 and 2 was obtained in the solid-state by X-ray crystallography [11] or in solution by NMR, diffusion NMR, [12] and small-angle neutron scattering.[13] Schalley and co-workers also studied these hexameric capsules in the gas phase. [14] However,t hese spectroscopic methods afford only limited information on the encapsulated molecules.Solid-state NMR has been used to study macromolecules and supramolecular systems, [15] but magic angle spinning solid-state NMR (MAS ssNMR) has been used only once to study dimeric capsules [15c] and never to study hexameric capsules.MAS ssNMR experiments yield detailed information on the structure and the dynamics of systems that are not amenable to crystallization. In X-ray studies of pyrogallol[4]arene hexamers [4,11] limited information, if any,w as obtained on the encapsulated guest molecules.T herefore in the present study we used MAS ssNMR to study the systems formed by slow evaporation of organic solutions of 2b,f ocusing on solvents which showed peculiar 1 HNMR resonance signals in solution for the encapsulated solvent molecules. [16] Figures 2A and 2B show the 1 Hand extracts of the 13 Ccross-polarization MAS (CPMAS) ssNMR spectra of the system obt...

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Capsule–Capsule Conversion by Guest Encapsulation

et al. 2016

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Guest-induced M 18 L 6 -M 24 L 8 capsule-capsule conversion is reported. Both capsules are composed of Pd II ethylenediamine units (M) and 1,3,5-tris(3,5-pyrimidyl)pyrimidine (L), and form trigonal bipyramidal (M 18 L 6 )a nd octahedral (M 24 L 8 )c losed-shell structures with huge hydrophobic inner spaces.T he M 18 L 6 trigonal bipyramid is converted to the M 24 L 8 octahedron through encapsulation of large aromatic guests,w ith the latter capsule possessing ac avity volume three times larger than the former.Despite the dynamic properties of the capsule host, the encapsulated guests are difficult to extract and are thus isolated from the external environment.Molecular capsules show unique host properties that are different from those of other synthetic hosts in that they possess isolated nanocavities that allow the properties and reactivities of encapsulated guests to be maintained.[1] Recently,al ot of effort has been put into constructing capsular structures of ever-increasing size, [2] but relatively few of these capsules show distinct guest-binding properties in their large cavities,t hus demonstrating that simple cavity expansion does not automatically lead to large guest encapsulation. We have previously reported trigonal bipyramidal M 18 L 6 coordination capsule 1a,b ut, unlike similar M 6 L 4 open cages that bind various organic guests in their cavities, [3] capsule 1a did not show any encapsulation behavior toward organic guests in water.[2b] We assumed that, in addition to the open framework, the highly electron-deficient environment of the M 6 L 4 cages offered by the metal-coordinated tris(4-pyridyl)triazine ligand is essential for guest binding.W etherefore redesigned the panel ligand of capsule 1a to give am ore electrondeficient 1,3-pyrimidine-cored panel, and created the more electron-deficient M 18 L 6 capsule 1b.H erein, we report that capsule 1b does indeed encapsulate large guests and, unexpectedly and surprisingly,t he large guest encapsulation triggers the conversion of M 18 L 6 capsule 1b into cavityexpanded M 24 L 8 octahedral capsule 2b (Figure 1). This guesttriggered M 18 L 6 -M 24 L 8 switch presents ar are example of capsule-capsule conversion with concurrent dramatic cavity expansion. [4] By simply mixing [(en)Pd(ONO 2 ) 2 ]( 3;e n= ethylenediamine) and our new ligand 2,4,6-tris(3,5-pyrimidyl)pyrimidine (4)i nw ater, trigonal bipyramidal M 18 L 6 coordination capsule 1b was obtained. Amixture of 3 (34.9 mg, 120 mmol) and 4 (12.6 mg, 40 mmol) was stirred in D 2 Osolution at 70 8 8C for 24 h, and the 1 HNMR spectrum after the complexation clearly showed the formation of as ingle product with panel ligand 4 placed in a C 2v environment. Six aromatic signals were observed in a1:2:2:2:2:1 integral ratio (Figure 2a), thus suggesting that 3 and 4 were assembled into trigonal bipyramid 1b with D 3h symmetry and am irror plane (s h ) vertical to the main apical C 3 axis.T here are many possible isomers of this M 18 L 6 capsular structure because ligand 4 does not have a C 3 symmetr...

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Efficient Loading and Kinetic Trapping of Hexameric Pyrogallolarene Capsules in Solution

Cited by 10 publications

References 34 publications

Encapsulation Studies of Cationic Gold Complexes within a Self‐Assembled Hexameric Resorcin[4]arene Capsule

Encapsulation Studies of Cationic Gold Complexes within a Self‐Assembled Hexameric Resorcin[4]arene Capsule

Hexameric Capsules Studied by Magic Angle Spinning Solid‐State NMR Spectroscopy: Identifying Solvent Molecules in Pyrogallol[4]arene Capsules

Capsule–Capsule Conversion by Guest Encapsulation

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