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The lower-rim functionalised distal bis-(4-picolyl)-p-tert-butylcalix[4]arene (L) selectively and quantitatively self-assembles into a series of discrete [2 + 2] blue-emitting metallacycles of general formula M2L2Xn with diverse metal salts (M = Zn2+, Pd2+, Ag+, and Cd2+; X = Cl−, NO3−, ClO4−, BF4− , CF3SO3−, PF6−, SbF6−; n = 2, 4). Macrocycle assembly has been corroborated by 2D-DOSY NMR and ESI-MS analyses, which further indicate that the M2L2Xn entities are quite stable and persist as robust and discrete macrocyclic species in solution. While free L units display modest blue emission (λmax = 307–405 nm), self-assembly of M2L2Xn results in amplified fluorescence (up to 13-fold). This remarkable enhancement may be primarily ascribed to the increase in conformational rigidity imposed on the L units by supramolecular assembly formation upon metal coordination to the pyridyl groups; in addition, subtle intensity-emission modulation may be provided by the different metal components. Titrations aimed at exploring the possibilities for ratiometric detection of metal cations or sensing of nitroaromatic species, revealed that the M2L2Xn platform may be a suitable “turn-on/off” system. Our results provide valuable insights into luminescence enhancement within the context of coordination-driven assemblies, which may be engineered to increase their fluorescence by imposing rigidity on the chromophores. [ABSTRACT FROM AUTHOR]

The reactions of mono-, bis- and tetrapicolyl-p-tert-butylcalix[4]arene derivatives functionalised in the phenolic positions (L1-L4) with copper(II) acetate resulted in the formation of discrete complexes or extended coordination polymers. The centrosymmetric dimer [Cu2(μ-O2CCH3)4(L1)2] 1, obtained with monodentate L1, has square pyramidal coordination around the copper centres and a cone conformer of monopicolyl-calix[4]arene acting as an axial ligand, with a molecule of acetonitrile hosted within its cavity. The potentially bidentate L2 acts as a monodentate ligand, affording the complex [Cu2(μ-O2CCH3)4(L2)2] 2, which based on spectroscopic and combustion analysis data has a similar coordination sphere around Cu(II). Compound L3 bridges two dicopper units in the coordination polymer [Cu2(μ-O2CCH3)4(μ-L3)]n 3, with the calixarene hosting a molecule of tetrahydrofuran. Finally, compound L4 reacts with 4 equivalents of copper(II) acetate, presumably generating a two-dimensional coordination polymer formulated as [{Cu2(μ-O2CCH3)4}2(L4)] 4. [ABSTRACT FROM AUTHOR]

The disubstituted calix[4]arene derivative 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-bis(2-pyridylmethoxy)calix[4]arene 2, which crystallises in the monoclinic space group P21/n, was functionalised in the phenolic O-H groups with (tert-butoxycarbonyl)methoxy groups. The yield of the isolated cone and partial-cone conformers of tetrasubstituted 5,11,17,23-tetra-tert-butyl-25,27-bis[(tert-butoxycarbonyl)methoxy]-26,28-bis(2-pyridylmethoxy)calix[4]arene 3a and 3b, depends on the identity of the alkali metal hydride employed to deprotonate 2. Partial-cone conformer 3b crystallises in the monoclinic space group P21/n, with an inverted (tert-butoxycarbonyl)methoxy-containing phenol moiety. The product distribution of 3a and 3b was interpreted based on the relative stabilities of the alkali metal complexes with the doubly deprotonated derivative of 2, and the monoanionic derivative [(tert-butoxycarbonyl)methoxy-2]- , by molecular mechanics analysis. [ABSTRACT FROM AUTHOR]

Investigates the mechanistic aspects of samarium-catalyzed redistribution of arene C-H and arylsilane Si-C bonds. Observation of the decomposition reaction of the compounds; Measurement on the law rate of the process; Activation of the Si-H.

Abstract: The synthesis of polydentate amine-S-arythiocarbamates was tested by directed ortho-lithiation of 2,4-disubstituted thiophenols, or the corresponding O- and S-arylthiocarbamates by deprotonation or lithium–bromine exchange, followed by addition of the electrophiles N(CH2CH2X)3 (X=Br, I). In the case of the thiophenol, deprotonation resulted in a trithioether-amine upon addition of the electrophile. With the O- and S-thiocarbamates, the reactions resulted in the migration of the thiocarbamoyl group to the ortho-position (Fries rearrangement), or nucleophilic attack of the carbonyl group by butyllithium, respectively. An alternative route employed 2,4-disubstituted phenols to obtain the corresponding salicylaldehydes, and subsequently the O-arylthiocarbamates for Newman–Kwart thermal rearrangement (NKR). Finally, the formyl group on the S-arylthiocarbamates allowed reductive amination to assemble polytopic compounds with amine and S-thiocarbamate groups. [Copyright &y& Elsevier]

Highlights: [•] Calix[4]arenes with one to four benzimidazole substituents were synthesized. [•] Heterotopic calix[4]arenes with mixed benzimidazole and styrene groups were prepared. [•] Copper(II) complexes with benzimidazole-calix[4]arene ligands were obtained. [•] Calix[4]arene-derivatives and their Cu(II) complexes were structurally and spectroscopically characterized. [ABSTRACT FROM AUTHOR]