Dietmar Kuck

Gas-phase basicities of the isomeric dihydroxybenzoic acids and gas-phase acidities of their radical cations

The thermochemical acid/base properties of the six dihydroxybenzoic acids (x,y-DHB) as prototypical matrices used in matrix-assisted laser desorption/ionization (MALDI) have been investigated. The ground-state gas-phase basicities (GB) of the six DHB isomers and the gas-phase acidities (ΔGacid) of the corresponding radical cations ([x,y-DHB].+) have been determined by Fourier-transform ion cyclotron resonance mass spectrometry employing the thermokinetic method. The gas-phase basicities vary from 814 kJ mol−1 for the least basic isomer, 3,5-DHB, to 831 kJ mol−1 for the most basic isomer, 2,4-DHB. The obtained gas-phase acidities of the corresponding radical cations vary from 815 kJ mol−1 for the most acidic species, 3,4-DHB, to 858 kJ mol−1 for the least acidic one, 2,5-DHB. The results indicate that ground-state proton transfer from the matrix radical cations to the analyte may play a role in the ionization process of MALDI, whereas proton transfer from protonated matrix molecules can be excluded.

C3v-symmetrical tribenzotriquinacenes as hosts for C60 and C70 in solution and in the solid state.

Various tribenzotriquinacenes (TBTQs), most of which incorporate six functional groups at the periphery of their C3v-symmetrical, rigid and convex-concave molecular framework, have been studied with respect to their ability to form supramolecular complexes with the C60 and C70 fullerenes, either in the solid state or in solution. The hexabromo derivative Br6-TBTQ was cocrystallized with C60 as [Br6-TBTQ<C60 x toluene] but, as studied by UV/vis and (1)H NMR spectroscopy, aggregation in benzene, toluene, or carbon disulfide solutions was not observed. Likewise, in contrast to the related C5v-symmetrical decakis(alkylthio)corannulenes, neither the parent hydrocarbon, nor a related hexamethoxy, or two hexakis(alkylthio) derivatives exhibited color, or complexation-induced chemical shift (CIS) changes with C60 or C70. The novel tris(2,3-thianthreno)triquinacene (o-S2C6H4)3-TBTQ, a TBTQ derivative extended by three 1,2-benzodithiino wings, and synthesized from Br6-TBTQ, was found to form 1:1 complexes with C60 and C70 in both benzene and toluene solutions. Association constants were determined for the respective complexes, viz. (o-S2C6H4)3-TBTQ<C60 (K(assoc) = 977 +/- 56) and (o-S2C6H4)3-TBTQ<C70 (463 +/- 49, both in benzene). The X-ray single crystal and molecular structures of the pure host and of the aggregates [(o-S2C6H4)3-TBTQ<2 C60 x 2.5 chlorobenzene] were also determined.

Multiply bridgehead- and periphery-substituted tribenzotriquinacenes - highly versatile rigid molecular building blocks with C-3v or C-3 symmetry

The chemical versatility of tribenzotriquinacenes as building blocks bearing rigid carbon frameworks with convex/concave molecular surfaces is presented. As revealed by X-ray single crystal structure analysis of the centro-methyl derivative, the tribenzotriquinacene skeleton adopts a perfect C-3v symmetrical conformation in the solid state. Within the crystal, the molecules are strictly aligned in stacks along the C-3v molecular axis of symmetry, at a distance of 6.0 Angstrom and with zero mutual rum along the axis. Bromination of the three benzhydrylic bridgeheads of the parent tribenzotriquinacene, of its centro-methyl homologue, in particular, and of its centro-ethyl homologue has opened a convenient access to a large variety of three-fold substituted or functionalized derivatives with C-3v Or C; molecular symmetry. Thus, several 1,4,7,10-tetrasubstituted tribenzotriquinacenes have become accessible bearing three hydrocarbon or heteroatomic groups in strictly eclipsed orientation with respect to the central substituent. A number of mono- and difunctionalized methyltribenzotriquinacenes have also been prepared. The potential of directed functionalization of the six peripheral positions of the aromatic rings, and of both the three benzhydrylic bridgeheads and the six peripheral positions of the tribenzotriquinacene framework is demonstrated with 1,4,7,10-tetramethyltribenzotriquinacene. The particular molecular topography of the tribenzotriquinacenes combined with their versatile functionalization renders these compounds promising building blocks for application in molecular and material design

C3-symmetrical tribenzotriquinacene derivatives: optical resolution through cryptophane synthesis and supramolecular self-assembly into nanotubes.

Based on a regioselective tris-formylation of a tribenzotriquinacene (TBTQ) hydrocarbon, the racemic C(3)-symmetrical TBTQ-trialdehyde and the corresponding TBTQ-trimethanol were synthesized along with their C(1)-isomers. Conversion of the C(3)-trialdehyde to three diastereomeric TBTQ-based cryptophanes occurring in high yield enabled the preparation of the optically pure C(3)-symmetrical TBTQ-trialdehydes and the determination of their absolute configuration. The racemic C(3)-symmetrical TBTQ-trimethanol was found to form several stable nanotubular aggregates in the solid state.

Tribenzotriquinacenes Bearing Six-Fold Benzofuran Extensions: Electron-Rich C3v-Symmetrical Hosts for C60

New tribenzotriquinacene (TBTQ) hosts bearing six-fold peripheral benzofuran functionalization have been synthesized. The three polycondensed arene wings were shown to operate optically independently and to generate deeply bowl-shaped C(3v)-symmetrical frameworks that act as relatively weak hosts toward C(60), as revealed by (1)H NMR spectroscopy.

Tribenzotriquinacenes with sixfold peripheral functionalization - Potential building blocks for novel organic networks

Hatlike tribenzotriquinacenes 1 that bear six identical functional groups at the peripheral positions of the benzene nuclei were synthesized as starting materials for the construction of convex-concave organic networks and other three-dimensional molecular frameworks. X=NO2 , NH2 , Br, I, SnBu, Ph, CCPh.

Unidirectional Molecular Stacking of Tribenzotriquinacenes in the Solid State: A Combined X‐ray and Theoretical Study

A combined X-ray diffraction and theoretical study of the solid-state molecular and crystal structures of tribenzotriquinacene (TBTQ, 2) and its centro-methyl derivative (3) is presented. The molecular structure of the parent hydrocarbon displays C3v symmetry and the three indane wings adopt mutually orthogonal orientations, similar to the case in its previously reported methyl derivative (3). Also similarly to the latter structure, the bowl-shaped molecules of compound 2 form infinite molecular stacks with perfectly axial, face-to-back (convex-concave) packing and with parallel and unidirectional orientation of the stacks. The experimentally determined intra-stack molecular distance is 4.75 Å for compound 2 and 5.95 Å for compound 3. Whereas the molecules of compound 2 show a slight alternating rotation (±6°) about the common axis of each stack, those of compound 3 show perfect translational symmetry within the stacks. We used dispersion-corrected density functional theory to compute the crystal structures of tribenzotriquinacenes 2 and 3. The London dispersion correction was crucial for obtaining an accurate description of the crystallization of both analyzed systems and the calculated results agreed excellently with the experimental measurements. We also obtained reasonable sublimation energies for both compounds. In addition, the geometries and dimerization energies of oligomeric stacks of compound 2 were computed and showed smooth convergence to the properties of the infinite polymeric stack.

A study of gaseous benzenium and toluenium ions generated from 1,4- dihydro- and 1-methyl-1,4-dihydro-benzoic acids

Gaseous benzenium C6H7+(1) and toluenium C7H9+(2) ions have been generated by mass spectrometric loss of ˙CO2H from the corresponding 1,4-dihydrobenzoic acids (3) and (4), and their fragmentations after ca. 10 µs have been investigated by means of mass-analysed ion kinetic energy (MIKE) spectrometry of some 2H and 13C labelled analogues. Metastable C6H7+ ions eliminate H2 after proton randomization, whereas metastable C7H9+ ions expel both H2 and CH4 after incomplete proton equilibration. In particular, 40% of C7H9+ ions randomize all their carbon and hydrogen atoms prior to loss of CH4, and 60% of C7H9+ ions lose the original methyl group along with a hydrogen atom from the (proton-equilibrated) benzenium ring, accompanied by a slow and incomplete exchange between the hydrogen atoms of the ring and the methyl group. It is suggested that loss of both CH4 and H2 occur via the (ipso-)toluenium ion (2). The role of a non-classical C7H9+ isomer, phenylmethonium ion (6), is discussed since striking similarities are found compared with [C6H6·CH3+]* adducts from ion–molecule reactions described in the literature.

Solid-State Enantiopure Organic Nanocubes Formed by Self Organization of a C3-Symmetrical Tribenzotriquinacene

Cubic aggregation: The racemic C(3)-symmetrical tribenzotriquinacene 1 was synthesized and found to crystallize in cubic aggregates consisting of eight homochiral molecules. The major driving force for this unique supramolecular aggregation may be attributed to the 24 equivalent sub-van der Waals interactions between the bromine atoms located at the convex surface of the triquinacene cores, rather than to polar interactions between the nitrobenzene units within and between the nanocubes.

Three orthogonal chromophores operating independently within the same molecule.

Three perylene bisimide chromophores were arranged orthogonally to each other within the same molecule by appropriate 3-fold coupling to 10-methyltribenzotriquinacene, a rigid C(3v)-symmetrical framework containing three indane units oriented at right angles in space. The electronic operation of the three chromophores was shown to be independent within the C(3)-symmetrical product, and potential applications of this novel molecular setup in molecular electronics are discussed.