Liliana Dobrzańska

Synthesis of functionalized dioxa-aza[7]helicenes using palladium catalyzed arylations.

Despite the recent reports on transition-metal catalyzed cycloisomerization strategies toward helicenes, the amount of palladium catalyzed routes remains rather scarce. Within this letter the successful preparation and characterization of novel dioxa-aza[7]helicenes using palladium mediated coupling reactions is presented.

Actuated Conformational Switching in a Single Crystal of a Homodithiacalix[4]arene

There are many reports discussing the conformational flexibility of calix[4]arenes in solution. On the other hand, similar studies concerning the solid state have received considerably less attention, even for the more extended and simultaneously more plastic calixarenes. Furthermore, no studies have been performed on single crystals, most likely because they are generally still perceived as unalterable and rigid, despite an increasing number of reports proving that the opposite is true. We report herein a phenomenon taking place in a single crystal of homodithiacalix[4]arene, the first member of a novel family of “homodiheteracalix[4]arenes”, with diatomic hetera bridges introduced in the macrocyclic ring, in this case disulfide. In contrast with the extensive literature on single-crystal-to-single-crystal transformations (SCSCT) taking place in metal–organic networks, the number of reports regarding SCSCT for organic solids is very limited to date and only encompasses a couple of examples. This is attributed to the fact that cooperative molecular motion is much more easily achieved for frameworks than in molecular crystals. To the best of our knowledge, reversible, solvent-induced conformational switching in a single crystal of an organic solid has not been reported to date. Moreover, the process is correlated with the formation/disappearance of channels in the structure. Jones et al. observed a change in conformation of an organic cage induced by solvent; however the single crystal did not survive this transformation, and a detailed study was performed on powdered bulk material instead. Keeping in mind that the structural changes observed in our case do not lead to loss of the crystal integrity, the transformation seems to be quite remarkable. The compound I (Scheme 1) was obtained by applying the concept of dynamic covalent chemistry (DCC), an attractive approach whereby a reversible reaction is performed under

Homoselenacalix[4]arenes: synthetic exploration and metallosupramolecular chemistry

Homoselenacalix[4]arenes were synthesized by a [2 + 2] reductive coupling protocol favouring the cyclotetramers. The inner and outer-rim decoration was varied and a bicyclic derivative was prepared by a similar one-pot procedure. Conformational analysis in solution and the solid state showed noticeable differences between the homoselenacalix[4]arenes and the analogous homothiacalix[4]arenes and provided insight into the metal binding potential of the Se-bridged macrocycles. The homoselenacalix[4]arenes were found to bind Ag(I). Complexation was visualized in the solid state and different packing networks were formed depending on the counter ions applied.

A Fragment-Based Approach toward Substituted Trioxa[7]helicenes

A series of novel substituted trioxa[7]helicenes have been successfully prepared by a one-pot palladium catalyzed C-H arylation reaction starting from readily prepared dibenzofuran fragments. The dinitro-substituted helicene was analyzed by X-ray crystallography revealing the occurrence of two distinct enantiomers in the asymmetric unit, which forms interesting supramolecular motifs in the crystal, based on weak H-bonding interactions.

Homodiselenacalix[4]arenes: Molecules with Unique Channelled Crystal Structures.

A synthetic route towards homodiselenacalix[4]arene macrocycles is presented, based on the dynamic covalent chemistry of diselenides. The calixarene inner rim is decorated with either alkoxy or tert-butyl ester groups. Single-crystal X-ray analysis of two THF solvates with methoxy and ethoxy substituents reveals the high similarity of their molecular structures and alterations on the supramolecular level. In both crystal structures, solvent channels are present and differ in both shape and capacity. Furthermore, the methoxy-substituted macrocycle undergoes a single-crystal-to-single-crystal transformation during which the molecular structure changes its conformation from 1,3-alternate (loaded with THF/water) to 1,2-alternate (apohost form). Molecular modelling techniques were applied to explore the conformational and energetic behaviour of the macrocycles.

Solvent diffusion through a non-porous crystal ‘caught in the act’ and related single-crystal-to-single-crystal transformations in a cationic dinuclear Ag(I) complex

The effect of a range of solvents on non-porous single crystals of a cyclic, dinuclear silver(I) complex with 1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (bitmb) with the formula [Ag2(bitmb)2](BF4)2 (1) was investigated by single crystal X-ray diffraction studies. It allowed us to get a few snapshots of the process of solvent diffusion through the crystal, connected with a series of reversible transformations. We have isolated disolvated 2a and monosolvated 2b forms with acetonitrile, monosolvated 3b and 4b forms with acetone and ethanol, respectively, and monosolvated 4c form with ethanol which is an intermediate between 1 and 4b. Longer exposure of the crystals to solvent vapours leads to the formation of a polymeric 1D Ag(I) complex with the general formula [Agbitmb(BF4)]n (5).

Synthetic protocols towards homodithiacalix[n]arenes

Synthetic procedures towards homodithiacalix[n]arenes are developed, starting from simple and readily available bifunctional aryl building blocks, by a dynamic covalent chemistry approach. Reaction of 1,3-bis(mercaptomethyl)-5-tert-butyl-2-methoxybenzene under basic conditions leads to a mixture of trimeric, tetrameric and pentameric dimethylenedithia-bridged cyclooligomers, whereas reaction of 5-tert-butyl-2-methoxy-1,3-bis(thiocyanatomethyl) benzene under reducing conditions (and subsequent oxidation) affords the homodithiacalix[4]arene macrocycle in a very selective fashion through efficient disulphide exchange chemistry.

Bis(di-2-pyridyl-amine-κN,N')bis-(thio-cyanato-κN)nickel(II).

The mononuclear neutral title complex, [Ni(NCS)2(C10H9N3)2], shows a cis-octahedral geometry around the NiII ion, formed by two chelating di-2-pyridylamine (Hdpa) ligands and two thiocyanate anions. Both amine H atoms are involved in N—H⋯S hydrogen bonding, resulting in the formation of layers of interlinked molecules parallel to the ab plane, which are further held together by weak π–π interactions between adjacent complexes, involving one ring of each dipyridylamine unit [centroid–centroid distance = 3.777u2005(4)u2005Å], forming a three-dimensional assembly.

2-(4-Meth-oxy-benz-yl)-4,6-diphenyl-2,5-diaza-bicyclo-[2.2.2]oct-5-en-3-one.

In the crystal structure of the title compound, C26H24N2O2, weak intermolecular C—H⋯π interactions involving the benzene of the p-methoxy benzyl group and one of the phenyl rings result in the formation of chains consisting of alternating enantiomers. Weak C—H ⋯O interactions with the methoxy O atom lead to the formation of layers, which are interlinked by further C—H⋯O interactions into a three-dimensional assembly.