Jason Ashmore

Preparation of solvent-free clathrand structures by the exclusion of an unwelcome guest

Crystallisation of clathrate host molecules, using an appropriate dual-nature solvent, can encourage both the growth of crystals and its exclusion as a guest. To achieve this end, the solvent should contain a part-structure that interacts favourably with the host molecules, thereby encouraging host association and crystal nucleation. It should also contain a part-structure that interacts unfavourably with the hosts, so that the solvent ultimately is excluded as the material crystallises. We report that trifluoromethylbenzene is an excellent solvent for obtaining crystalline solvent-free clathrands belonging to the diquinoline inclusion family. The X-ray crystal structures of one of these and its corresponding toluene inclusion compound are described and compared.

Assembly of brick-like aromatic edge–face (EF)6 host dimers into lattice inclusion compounds

7,15-Dibromo-8,16-diphenyl-6,7,14,15-tetrahydro-6,14-methanocycloocta[1,2-b : 5,6-b′]diquinoline 4 has been synthesised and found to form lattice inclusion compounds with a wide range of guests. The host molecules associate into centrosymmetric brick-like dimers by means of multiple aromatic edge–face (EF) interactions. These (EF)6 units then pack as layers with the guests occupying inter-brick spaces. Differences in tilt and/or translation of the dimers, along with changes in host–guest association, permit accommodation of guest molecules with differing sizes and shapes. The X-ray structures of the 1 : 1 compounds of 4 with chloroform and p-xylene are contrasted.

The effect of chlorine substitution on the inclusion properties of a diquinoline host molecule

The chloro-substituted diquinoline compounds 7 and 8 have been synthesised as part of our continuing search for new host molecules. As intended, the latter forms lattice inclusion compounds with a range of molecules, and here the X-ray structures of (8)4·(benzene)5 and (8)·(toluene) are described. Host 8 exhibits entirely different inclusion behaviour compared to its parent non-chlorinated analogue 2. Edge–edge double C–H⋯N synthons, normally ubiquitous in inclusion structures formed by members of this diquinoline host family, vanish when 8 is used. Instead there is increased dependence on halogen–halogen and aryl–aryl interactions. Despite the similarity of the guests, the structures of the two inclusion compounds are very different. Crystal engineering analysis reveals, however, that the supramolecular synthons present in the two cases are very similar.

Formation of 3-azabicyclo[3.3.1]non-3-enes: imino amides vs. imino alkenes

Abstract An effective method for synthesising alkaloid-like compounds containing the 3-azabicyclo[3.3.1]non-3-ene core structure was successfully carried out in a stereoselective manner via the bridged-Ritter reactions. Important optically active 6-alkyl(aryl)amido-4-alkyl(aryl)-2,2,6-trimethyl-3-azabicyclo[3.3.1]non-3-enes (imino amides) and 4-alkyl(aryl)-2,2,6-trimethyl-3-azabicyclo[3.3.1]nona-3,6-dienes (imino alkenes) were obtained in one step from (−)-β-pinene and the respective nitriles in the presence of concentrated H2SO4. The relative compositions of these products were controlled by varying the reaction conditions. Kinetic studies were conducted to enable a mechanistic understanding of the reaction pathways.Graphical Abstract

The structural convergence of two aromatic inclusion host families

The Weber multi-ring aryl hydrocarbons 1–4, dihalo diheteroaryl 6,8, and tetrahalo aryl 10,12 compounds are examples of host molecules from well-known families of lattice inclusion systems. Despite these three systems having a number of features in common, no attempt has been made previously to establish their inter-relationship. In this work, the diheteroaryl ring system of 5 has been substituted with two and four pendant phenyl groups to give the non-halogenated compounds 15 and 17, respectively. In common with typical unsubstituted diheteroaryl compounds (such as 5 and 7), compound 15 shows no host properties. On the other hand, 17 can include several different guests and therefore its behaviour represents a cross-over into the Weber system. Crystal engineering aspects of the X-ray structures of 15, (17)·(chloroform) and (17)·(toluene) are analysed in this light.

Inclusion of polyhalomethanes by a tetrahalogenated diquinoline host

The dichloro diphenyl diquinoline 7 and its dibrominated derivative 4 do not crystallise as structures assembled from the dimeric aryl (EF)6 brick-like unit used by their non-chlorinated analogues. Instead, several other types of intermolecular assembly are employed. Compound 4 forms lattice inclusion compounds when recrystallised from polyhalomethanes but yields the apohost structure from other solvents. The X-ray structures, supramolecular synthons, molecular packing, and crystal energies, of this series of compounds are described and compared.

Synthesis and inclusion properties of new nitrated C2− symmetric diquinoline hosts

The non-host 6,7,14,15-tetrahydro-6,14-methanocycloocta[1,2-b : 5,6-b′]diquinoline3 was nitrated to yield its C2− symmetric dinitro analogues 6 and 7. Both derivatives acted as lattice inclusion hosts in accord with our molecular design. The four X-ray crystal structures reported proved to be very different from each other and are analysed and compared. Although the nitro group does participate in weak intermolecular associations, its major function is shown to be a spoiler group that disrupts simple packing and thereby encourages guest inclusion.

5bα,6,7,13bα,14,15-Hexahydro­acridino[4,3-c]acridine

The racemic title compound, C24H20N2, gives spontaneous resolution with the formation of conglomerate crystals in the space group P212121 when crystallized from ethyl acetate. The twisted molecules pack in parallel regions (ab plane) which then form a herringbone pattern along c.

2,3,10,11-Tetra­meth­oxy-6,7,14,15-tetra­hydro-6,14-methano­cyclo­octa­[1,2-b;5,6-b′]diquinoline

The racemic title compound, C27H26N2O4, crystallizes with its central carbon bridge on a twofold axis. It forms parallel chains of molecules utilizing aryl offset face–face interactions with an interplanar distance of about 3.5 Å. These chains associate further by means of pairs of O—CH2—H⋯π (with H–ring distances ranging from 2.69 to 2.95 Å) and O—CH2—H⋯N motifs. The methoxy groups in this structure are coplanar with the aromatic rings to which they are attached. This is recognized as being common behaviour amongst aromatic methoxy compounds.