Imidazolium units represent the main structural motifs for the formation of unconventional C-H•••Cl 2 hydrogen bonds which become the noncovalent forces driving the anion interactions exibited by dicationic [1 4 ]imidazoliophanes in the solid state, while C-H•••O hydrogen bonds with water play a crucial role in governing the conformation of the solid-state aggregates, as well as in solution, wherein NMR studies also reveal the importance of hydrogen bonds in controlling the tendency to anion binding.

The synthesis of simple imidazolium-based ligand precursors containing a 1,3-alkylidene-2,4,6-trimethylbenzene spacer was examined and different synthetic protocols were applied depending on the nature of the alkylidene arm. For a methylene arm, simple dications 5a,b.2CI were obtained directly. The higher homologue counterparts were conveniently prepared by general multistep routes following a five-step sequence for ethylene dications 6a,b.2Br or a six-step sequence for propylene dications 7a,b.2Br in > or = 52% overall yield. Imidazolium salts based on the shorter methylene spacer were used to prepare palladium complexes (17-20) with N-heterocyclic carbenes via transmetallation from well-defined silver compounds or directly in basic conditions. In order to facilitate spectroscopic characterisation of the palladium species two [Pd(allyl)(bis-oxazoline)]+ (25-26) complexes with the same ligand bridge were synthesized. [PdX2bisL] complexes appeared in solution as mixtures of species, mononuclear with cis- or trans-geometry or oligomeric compounds. The reaction of [PdCl(allyl)]2 and micro-bis(carbene)(AgX)2 complexes in 1 : 1 or in 0.5 : 1 ratio leads to binuclear compounds [Pd2Cl2(allyl)2(micro-bis-carbene)] (19a,19b) and to very labile monomeric [Pd(allyl)(bis-carbene)]+ (20a,20b) compounds, respectively. The preparation of analogous [Pd(allyl)(bis-oxazoline)]+ complexes showed the formation of one of the four possible isomers. [Pd(allyl)(bis-oxazoline)]PF6 complexes were inactive as catalytic precursors in the allylic substitution reaction.

No abstract

A broad and simple method permitted halide ions in quaternary heteroaromatic and ammonium salts to be exchanged for a variety of anions using an anion exchange resin (A− form) in non-aqueous media. The anion loading of the AER (OH− form) was examined using two different anion sources, acids or ammonium salts, and changing the polarity of the solvents. The AER (A− form) method in organic solvents was then applied to several quaternary heteroaromatic salts and ILs, and the anion exchange proceeded in excellent to quantitative yields, concomitantly removing halide impurities. Relying on the hydrophobicity of the targeted ion pair for the counteranion swap, organic solvents with variable polarity were used, such as CH3OH, CH3CN and the dipolar nonhydroxylic solvent mixture CH3CN:CH2Cl2 (3:7) and the anion exchange was equally successful with both lipophilic cations and anions.

Efficient access to the bis(imidazolyl)calixarene 2 and dicationic bis(imidazolium) salts 1a,b x 2X directly bonded to the upper rim of calixarene structure has been reported. Anion binding properties of the new receptors were studied by 1H NMR spectroscopic methods. Bis(N-butylimidazolium) dication 1a exhibited the best recognition properties toward carboxylate anions with a 1:1 receptor-anion binding stoichiometry, whereas the presence of a bulky group such as isopropyl (1b) increased the difficulty of both imidazolium moieties to be able to support the association with the same single anion.

The significance of the reported dicationic [14]imidazoliophanes 4·2X relies on their ability to bind anions in polar media. Thus, imidazolium units represent the main structural motifs in the formation of unconventional (C–H)+···Cl– charge‐assisted hydrogen bonds which become the noncovalent forces driving the anionic interactions exhibited by dications 4·2X. Herein, we report the “3+1” convergent synthesis of the title macrocycles 4a–d·2X; their counteranion exchange using a strongly basic anion‐exchange resin (OH– form) and their structures have been examined by NMR spectroscopy. Solution studies in CD3CN and [D6]DMSO by 1H NMR spectroscopy have revealed the importance of the hydrogen bonds in controlling anion recognition.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A series of novel indene derivatives designed by a scaffold selection gave access to several examples of (Z)-arylmethylideneindenes and indenylsulfonamides that acted as serotonin 5-HT(6) receptor ligands. Different synthetic multistep routes could be applied to these target compounds, each with their own complexity and limitations. A reasonable route involved the (3-indenyl)acetic acids as the key intermediates, and two alternatives were also examined. The first protocol used was a two-step sequence employing a modified Horner-Wadsworth-Emmons reaction, but better results were obtained with a procedure based on the condensation of indanones with the lithium salt of ethyl acetate, followed immediately by dehydration with acid and hydrolysis/isomerization under basic catalysis. (3-Indenyl)acetic acids were transformed to the corresponding acetamides, which were effectively reduced to indenylsulfonamides using an optimized procedure with AlH(3)-NMe(2)Et. The binding at the 5-HT(6) receptor was with moderate affinity (K(i) = 216.5 nM) for the (Z)-benzylideneindenylsulfonamide and enhanced affinity for the simple indenylsulfonamide counterpart (K(i) = 50.6 nM). Selected indenylsulfonamides were then tested, showing K(i) values as low as 20.2 nM.

Scaffold selection involving an indole-to-indene core change led to the discovery of a series of indenylsulfonamides that act as 5-HT6 serotonin receptor agonists. The variety of the targeted ligands and their synthetic complexity required multistep synthetic approaches. The novel indenylsulfonamides exhibited variable binding affinities for the 5-HT6 receptor, and the in vitro primary binding profiles of the preferred compounds revealed them to be 5-HT6 receptor agonists with Ki values > or =4.5 nM. The structural changes responsible for enhancing the affinities indicated a directing effect modulated by the nature of the indene core, the substitution at the aminoethyl side chain, and especially by the aryl(heteroaryl)sulfonyl group on the indene 5-position. A representative of the family, the N-(inden-5-yl)imidazothiazole-5-sulfonamide (43), exhibited a high affinity and functioned as a potent full agonist for the 5-HT6 receptor (Ki = 4.5 nM, EC50 = 0.9 nM, Emax = 98%).