Hydrogen-bond-induced selectivity of a head-to-head photo-dimerisation of dialkynylanthracene - access to tetradentate Lewis acids

Using 2-hydroxypropyl-protecting groups, 1,8-dialkynylanthracene photo-dimers were prepared in head-to-head-configuration by UV irradiation on a multi-gram scale. In non-polar solvents, the combination of non-covalent hydrogen bonds and π-π-interactions induces the formation of the syn-isomer in up to 85% yield. Instead, more polar solvents or irradiation of unprotected 1,8-diethynylanthracene led to formation of the corresponding anti-isomer in large excess. Cleavage of the protecting groups under basic conditions affords a rigid hydrocarbon skeleton with four directional functions. This was used as a building block for a tetradentate boron Lewis acid. Its applicability as a host for Lewis-base substrates was demonstrated by the formation of adducts with various nitrogen bases. Adduct formation with hydrazine leads to impressive networks between the tetraboron host and the substrate molecules.

1,8,10-Substituted Anthracenes – Hexafunctional Frameworks via Head-to-Tail Photodimerisation

Several 1,8,10-functionalised anthracene derivatives and a couple of 1,8,9-functionalised anthracene analogous, bearing alkynyl substituents at positions 1 and 8 were synthesised and their photochemistry investigated in UV irradiation experiments. Almost all compounds could be converted into their 9,10:10′,9′-head-to-tail photodimers completely excluding the formation of the corresponding head-to-head isomers. Working under non-inert conditions led to formation of endoperoxides in some cases. Furthermore, a non-classical [4π+2π] photodimer was obtained from 1,8,10-tris[(trimethylsilyl)ethynyl]anthracene with one of the alkynyl substituents involved in the photoreaction. The 1H and 13C NMR spectra of all classical and non-classical photodimers were compared with those of the endoperoxides identifying characteristic shifts for the atoms at positions 9 and 10. Moreover, solid-state structures were determined for one or more of each representative.

A Rational Approach to Tetra-Functional Photo-Switches

α,ω-Bis(1,8-dichloroanthracen-10-yl)alkanes with (CH₂) _n -linker units (n=1-4) were synthesized starting from 1,8-dichloroanthracen-10(9H)-one. This was transformed into anthracenes with allyl, bromomethyl and propargyl substituents in position 10; these were converted in various C-C-bond formation reactions (plus hydrogenation), leading to two anthracene units flexibly linked by α,ω-alkandiyl groups. 1,2-Ethandiyl- and 1,3-propandiyl-linked derivatives were functionalized with ethynyl groups in positions 1, 8, 1' and 8', and these terminally functionalized by Me₃Sn groups using Me₂NSnMe₃. All linked bisanthracenes were subjected to UV light induced cyclomerization and a series of 9,10 : 9',10'-photo-cyclomers were obtained. Their thermal cycloreversion and (repeated) switchability was demonstrated. 1,3-Bis{1,8-bis[(trimethylstannyl)ethynyl]anthracen-10-yl}propane served as model compound for photo-switchable acceptor molecules and its open and closed forms were characterized by NMR and DOSY experiments.

Bidentate Boron Lewis Acids: Selectivity in Host-Guest Complex Formation

Bidentate boron Lewis acids based on 1,8-diethynylanthracene were synthesised in two steps by initial stannylation of the terminal alkynes and subsequent tin-boron exchange with different chloroboranes. The reactions were very selective, and the target compounds were obtained in high purity and good to excellent yields. Complexation experiments of 1,8-bis[(diphenylboranyl)ethynyl]anthracene with nitrogen bases (pyridine, pyrimidine, TMEDA) afforded three stable adducts, which were structurally characterised by X-ray diffraction. Competition experiments demonstrated the selective exchange of guests, and quantum-chemical calculations provided information on their energetics. NMR experiments at low temperature gave insight into the dynamic behaviour of the TMEDA adduct.

Aurophilicity in action: stepwise formation of dinuclear Au(i) macrocycles with rigid 1,8-dialkynylanthracenes

1,8-Bis(gold(i)-ethynyl)anthracene units find stabilisation by maximising aurophilic contacts under formation of macrocyclic anions linked to cationic gold(i) fragments.

Syntheses, Solid State Structures and Photochemistry of α,ω-Bis-[(1,8-dichloroanthracen-10-yl)dimethylsilyl]alkanes

Starting from 10-bromo-1,8-dichloroanthracene, a series of 1,8-dichlorinated anthracene derivatives, flexibly bridged in position 10 by –Me2Si– and –Me2Si–(CH2) n –SiMe2– linker units, were synthesised. The linked anthracenes were generated by converting (1,8-dichloroanthracen-10-yl)lithium with chlorosilanes in salt-elimination reactions. The bichromophors were tested in UV light induced photo reactions. None of the new compounds yielded any intra- or intermolecular photoproduct. All α,ω-(dimethylsilyl)alkane-linked bisanthracenes decomposed to give 1,8-dichloro-9-hydroxyanthracen-10(9H)-one in the presence of oxygen. A completely different behaviour was shown by the bisanthracenyldimethylsilane, undergoing a 9,10:3′,4′-photocyclomerisation reaction. The new compounds were characterised by NMR spectroscopy, mass spectrometry and in most cases by X-ray diffraction studies.

Improved Access to 1,8-Dichloro-10-(ethynyl)anthracene: A Useful Building Block for (Semi-)rigid Organic Frameworks

An easy access to 1,8-dichloro-10-(ethynyl)anthracene is reported, which is widely applicable for building up rigid linkers between two 1,8-dichloroanthracene units. For this, 1,8-dichloroanthren-10(9H)-one was reacted with ethynylmagnesium bromide in the presence of CeCl3; the yield was 65%. This building block was used as a substrate in (cross-)coupling reactions and some examples of linked 1,8-dichloroanthracen-10-yls (e.g., 1,8-bis[(1,8-dichloroanthracen-10-yl)-ethynyl]naphthalene or 1,2-bis[(1,8-dichloroanthracen-10-yl)ethynyl]-benzene) were synthesized in good to moderate yields. Linked 1,8-dichloroanthracen-10-yl derivatives were also synthesized by cross-coupling reactions using 10-bromo-1,8-dichloroanthracene and doubly ethynyl-substituted substrates. Linkers between the 1,8-dichloroanthracene units were: butadiynediyl, dimethylsilyldiethynyl, octa-1,7-diyne-1,8-diyl, propane-1,3-diylbis(dimethylsilyl)diethynyl, benzene-1,2-diethynyl, naphthalene-1,8-diyldiethynyl, and anthracene-1,8-diyldiethynyl. The new anthracene compounds were characterized by NMR spectroscopy, high-resolution mass spectrometry, and, in part, by X-ray diffraction experiments.