Deepening Cavitands

Hydrogenation Versus Hydrosilylation: The Substantial Impact of a Palladium Capsule on the Catalytic Outcome

A palladium capsule, made of three cavitands, namely P,P-dichlorido{5,17-bis[5-(diphenylphosphanyl)-4(24),6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]arenyl-17-oxymthyl]-4(24),6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]arene}palladium(II) (1), was synthetized by coordination of the corresponding diphosphinated ligand and the palladium precursor [PdCl2(PhCN)2] in 27% yield. The obtained P,P-chelate complex was fully characterized by elemental analysis, NMR and mass spectrometry. Molecular dynamics simulations carried out on the metallo-capsule showed the structure made by the three cavitands was slightly distorted over the 1 μs of the simulation. The evaluation of the palladium capsule 1 in the reaction between arylacetylenes and Et3SiH in undried conditions unequivocally demonstrates a drastic change in chemoselectivity, with the formation of the partially hydrogenation product rather than the hydrosilylation products observed with complexes whose active center is more accessible, for instance [PdCl2(PPh3)2].

A calix[3]carbazole-based cavitand: synthesis, structure and its complexation with fullerenes

A calix[3]carbazole-based cavitand was conveniently synthesized. It was found that the cavitand with adjustable conformation could show excellent complexation with fullerenes C60 and C70 in both solution and the solid state. Moreover, the crystal structures of the host-guest complexes show that the cavitand can stack into channel-like architectures, in which fullerenes are orderly arranged inside.

Negative Cooperativity in Guest Binding of a Ditopic Self-Folding Biscavitand

A brand-new self-folding biscavitand was synthesized from a feet-to-feet-connected bisresorcinarene. The X-ray crystal structure of the biscaivtand showed that the two cavities are tightly connected with four butylene linkages. The conformationally coupled two cavities accommodated two cationic guests, showing a homotropic negative cooperativity in nonpolar solvents (toluene and chloroform). A polar tetrahydrofuran solvent weakened the cyclic hydrogen bonding interactions of the biscavitand, which resulted in noncooperative guest binding.

Recent Advances in Halogen Bonded Assemblies with Resorcin[4]arenes

Resorcinarenes are cavity-containing compounds when in the crown conformation, from the calixarene family of concave compounds. These easy to synthesize macrocycles can be decorated at the upper rim through the eight hydroxyl groups and/or the 2-position of the aromatic ring. They are good synthons in supramolecular chemistry leading to appealing assemblies such as open-inclusion complexes, capsules and tubes through multiple weak interactions with various guests. Halogen bonding (XB) is a highly directional non-covalent interaction by an electron-deficient halogen atom as a donor that interacts with a Lewis base, the XB acceptor. This tutorial review provides an overview of recent advances in halogen-bonded assemblies based on resorcinarenes and their derivatives, specifically focusing on discrete and capsular assemblies.

One-Step Synthesis of C2v-Symmetric Resorcin[4]arene Tetraethers

The three-component reaction between a resorcinol, 1,3-dimethoxybenzene, and an alkyl aldehyde (R = C₁-C₁₁) along with BF₃·OEt₂ affords a C_2v-symmetric resorcin[4]arene tetraether in one step; in most cases, the single isomer can be precipitated from the reaction mixture in moderate to excellent yields (up to 89%). The reaction is tolerant of 2-substituted resorcinols (R' = OH, Cl, Br, Me), allowing a third type of functionality to be regioselectively incorporated during the macrocyclization.

A resorcinarene-based tetrabenzoimidazolylidene complex of rhodium

A tetrabenzoimidazolium-resorcinarene cavitand was used for the preparation of a tetra-benzoimidazolylidene of rhodium, which is unprecedented in the field of poly-NHC metal complexes. Both the experimental and computational analyses of the molecule reveal a distorted vase conformation as the most stable one, although several non-interconverting conformational isomers due to the restricted rotation about the Rh-C(carbene) bond coexist in the product. There is a fluxional behaviour involving the vase-kite interconversion. The main interactions between the arms of the cavitand are mostly concentrated on the terminal organometallic fragments attached to NHC, along with those between -CH₃ and a N-heterocyclic carbene ring from benzoimidazoles.

One-dimensional arrangement of NORIA in the solid-state

NORIA is a synthetic macrocycle consisting of twelve resorcinol rings. By cocrystallization of NORIA with benzene, NORIA organized one-dimensional array.

Upper-rim functionalization and supramolecular polymerization of a feet-to-feet-connected biscavitand

An octaiodobiscavitand was synthesized via an aromatic Finkelstein iodination reaction in good yield. An octa-functionalized biscavitand self-assembled to form a supramolecular polymer in the solid state.

Synthesis of tetra-pincer nickel(ii) and palladium(ii) complexes of resorcin[4]arene-octophosphinite [Res(OPR2)8] and rhodium-catalyzed regioselective hydroformylation reaction

This paper describes the synthesis of resorcin[4]arene based octaphosphinite ligands and their tetra-pincer Ni^II and Pd^II complexes and rhodium-octaphosphinite catalyzed hydroformylation of styrene and its derivatives.

Chiral chromane[4]arenes synthesised by cycloaddition reactions ofo-quinomethine resorcin[4]arenes

The synthesis of cavity-extended cyclochiral heterocyclic derivatives of chromane[4]arenes by a cycloaddition reaction between theo-quinomethine derivative of resorcin[4]arene and various styrenes is described.

Bowl-in-bowl complex formation with mixed sized calixarenes: adaptivity towards guest binding

We demonstrated the organization of two differently sized calixarenes C-methylresorcin[4]arene (RsC1) and either calix[6]arene (Calix6) or calix[8]arene (Calix8), where the lower rim of RsC1 partially overlaps with the upper rim of Calix6 or Calix8. An adaptive nature of the heteromacrocyclic assembly towards the binding of a model guest has been observed.

Rigid tetraarylene-bridged cavitands from reduced-symmetry resorcin[4]arene derivatives

Two tetraaryl-extended macrocycles were prepared from resorcin[4]arenes. The C_2v-symmetric isomer afforded a new rigid cyclooctaphenylene cavitand following oxidative cyclodehydrogenation.

A Tetraferrocenyl-Resorcinarene Cavitand as a Redox-Switchable Host of Ammonium Salts

Tetraannulation of a resorcinarene-octaamino cavitand with ferrocenecarboxaldehyde allows the preparation of a tetrabenzimidazole-resorcinarene cavitand with four ferrocenyl moieties directly linked to the C2 atom of the imidazole units. Oxidation of the four ferrocenyl moieties produces important structural modifications of the molecule, as indicated by DFT calculations performed for the neutral and tetraoxidized forms of the cavitand. By means of (1) H NMR spectroscopic analysis, the encapsulating properties of the new tetraferrocenyl-resorcinarene cavitand toward a series of ammonium salts were evaluated, and a clear cutoff point in binding affinity with respect to size was observed. Cyclic voltammetric studies allowed us to estimate the relative association constants for the neutral and oxidized forms of the cavitand, thus indicating that the guest was bound to the neutral (reduced) state of the cavitand and was released from the oxidized form. These redox-addressable conformational and binding properties of the resorcinarene-tetraferrocenyl cavitand constitute all the necessary features of a redox-switchable molecular gripper. By means of mass-spectrometric analysis, we could unambiguously confirm the molar stoichiometry of the host-guest complex (1:1) and assess the strong guest encapsulation, as indicated by triggering the covalent coupling between host and guest in the gas phase.

Methylresorcinarene: a reaction vessel to control the coordination geometry of copper(II) in pyridine N-oxide copper(II) complexes

Pyridine and 2-picolinic acid N-oxides form 2 : 2 and 2 : 1 ligand : metal (L : M) discrete L2M2 and polymeric complexes with CuCl2 and Cu(NO3)2, respectively, with copper(ii) salts. The N-oxides also form 1 : 1 host-guest complexes with methylresorcinarene. In combination, the three components form a unique 2 : 2 : 1 host-ligand-metal complex. The methylresorcinarene acts as a reaction vessel/protecting group to control the coordination of copper(ii) from cis-see-saw to trans-square planar, and from octahedral to square planar coordination geometry. These processes were studied in solution and in the solid state via(1)H NMR spectroscopy and single crystal X-ray diffraction.

Multifold ring closing metathesis reactions in the formation of resorcin[4]arene cavitands

The formation of the resorcin[4]arene cavitands by the ring closing metathesis (RCM) reaction depends, to a large extent, on the conformation and the substituents on the upper and lower rim of the perallylated resorcin[4]arenes.

¹⁹F NMR fingerprints: identification of neutral organic compounds in a molecular container

Improved methods for quickly identifying neutral organic compounds and differentiation of analytes with similar chemical structures are widely needed. We report a new approach to effectively "fingerprint" neutral organic molecules by using (19)F NMR and molecular containers. The encapsulation of analytes induces characteristic up- or downfield shifts of (19)F resonances that can be used as multidimensional parameters to fingerprint each analyte. The strategy can be achieved either with an array of fluorinated receptors or by incorporating multiple nonequivalent fluorine atoms in a single receptor. Spatial proximity of the analyte to the (19)F is important to induce the most pronounced NMR shifts and is crucial in the differentiation of analytes with similar structures. This new scheme allows for the precise and simultaneous identification of multiple analytes in a complex mixture.

New lanthanide–CB[6] coordination compounds: relationships between the crystal structure and luminescent properties

Four new isostructural complexes were obtained with Ln³⁺ and CB[6]. The compounds present interesting spectroscopic properties, not observed before in Ln–CB[n] compounds.

Cyclochiral resorcin[4]arenes as effective enantioselectors in the gas phase

The effect of cyclochirality of rccc-2,8,14,20-tetra-n-decyl-4,10,16,22-tetra-O-methylresorcin[4]arene (C) on the enantiodiscrimination of a number of chiral bidentate and tridentate aromatic and aliphatic biomolecules (G) has been investigated by nano-electrospray ionization (nano-ESI)-Fourier transform ion cyclotron resonance mass spectrometry. The experimental approach is based on the formation of diastereomeric proton-bound [C·H·G](+) complexes by nano-ESI of solutions containing an equimolar amount of quasi-enantiomers (C) together with the chiral guest (G) and the subsequent measurement of the rate of the G substitution by the attack of several achiral and chiral amines. In general, the heterochiral complexes react faster than the homochiral ones, except when G is an aminoalcoholic neurotransmitter whose complexes, beyond that, exhibit the highest enantioselectivity. The kinetic results were further supported by both collision-induced dissociation experiments on some of the relevant [C(2) ·H·G](+) three-body species and Density functional theory (DFT) calculations performed on the most selective systems.