Poly-Lewis-acids based on bowl-shaped tribenzotriquinacene

Host-guest chemistry of tridentate Lewis acids based on tribenzotriquinacene

Flexible poly-Lewis acids (PLA) based on the tribenzotriquinacene (TBTQ) scaffold have been synthesised. Hydrosilylation of 4b,8b,12b-triallyltribenzotriquinacene and subsequent exchange of the chlorine substituents with weaker coordinating triflate groups afforded a novel triple silyl-functionalised PLA. By regioselective hydroboration of triallyl-TBTQ with various organoboranes, PLAs with different Lewis acidities were obtained. The synthesised PLAs were combined with neutral bases in host-guest experiments. DOSY NMR spectroscopy was performed to elucidate the complexation process in solution. These experiments revealed a highly dynamic interaction between the boron-functionalised PLA and triazine. However, the addition of one equivalent of tris(dimethylphosphino(methyl))phenylsilane led to the formation of a 1 : 1 adduct, which was confirmed by diffusion experiments.

Tridentate Lewis Acids Based on Tribenzotriquinacene Chalices

Chalice-shaped tridentate poly-Lewis acids (PLA) based on the tribenzotriquinacene (TBTQ) scaffold have been synthesised. Stannylation of the alkyne units, attached via phenyl-spacers to the benzhydrylic positions to the TBTQ scaffold, with Me2NSnMe3 afforded the trimethyltin substituted TBTQ derivative. Replacement of these tin functions with other elements resulted in rigid boron- and aluminium-functionalised PLAs. More flexible PLAs were obtained by hydrometallation reactions of the terminal alkyne groups of 4b,8b,12b-tris((ethynyl)phenyl)tribenzotriquinacene. The resulting poly-Lewis acids were tested for their acceptor abilities in host-guest experiments with suitable bases. Preliminary tests with pyridine led to the synthesis of a large tridentate base with three pyridyl groups attached to a TBTQ backbone. Complexation of this Lewis base with the PLAs resulted in the formation of aggregates, which were studied in solution in more detail by 1H DOSY NMR experiments regarding their size. Further experiments were performed with the tridentate bases 1,4,7-trimethyl-1,4,7-triazacyclononane and tris((dimethylphosphino)methyl)phenylsilane.

Hexadentate poly-Lewis acids based on the bowl-shaped tribenzotriquinacene

Hexadentate poly-Lewis acids (PLA) based on the bowl-shaped tribenzotriquinacene (TBTQ) have been synthesised. The introduction of three n-propyl groups into the benzhydrylic positions of the TBTQ backbone has significantly increased the solubility of the subsequently derived compounds. Semi-flexible PLAs containing boron and aluminium were obtained by hydrometallation of the corresponding 2,3,6,7,10,11-hexaalkynyl-TBTQ. Other rigid hexadentate PLAs were synthesised by stannylation of the corresponding alkyne units with Me3SnNMe2 followed by tin-element exchange reactions. The Lewis acidity of these PLAs was investigated in host-guest experiments with pyridine. Further experiments with bidentate bases showed correlations between their flexibility, their Lewis basicity and the complexation behaviour towards the synthesised PLAs. Addition of bis((dimethylphosphino)methyl)dimethylsilane (BisPhos) to solutions of the rigid alkynyl PLAs led to the formation of 3 : 1 adducts. Single crystal X-ray diffraction was used to further elucidate the host-guest connectivtiy. In addition, a sixfold pnictogen-bonding donor was synthesised by tin-antimony exchange.

Synthesis of bi- and tetradentate poly-Lewis acids by hydroalumination of poly-alkynyl-anthracene derivatives

Photo-dimers of 1,5-diethynylanthracene and 1,5-bis[(trimethylsilyl)ethynyl]anthracene, obtained by UV radiation of the monomers, were treated with the bulky aluminium hydride [(SiMe₃)₂HC]₂AlH in hydroalumination reactions. Hydroalumination of the tetraethynyl-substituted anthracene photo-dimers (syn and anti) led to fourfold aluminium-functionalized Janus-like products with two aluminium functions on each side oriented towards the same direction. The reactions of the monomeric anthracene derivatives with [(SiMe₃)₂HC]₂AlH afforded semi-flexible bidentate Lewis acids, which are interesting building blocks for molecular chains bearing multiple Lewis-acidic functions. The aluminium-functionalized anti-photo-dimer was treated with various donor molecules to gain insight into its host-guest chemistry. All poly-Lewis acids and their adducts were characterized by X-ray diffraction experiments, multinuclear NMR spectroscopy and by elemental analyses.

Chalice-Type Tridentate Silicon Lewis Acids of C3 Symmetry in a Single Step Starting from Hexadehydrotribenzo[12]annulene

Tridentate Lewis acids with aligned functions were synthesized based on the rigid framework hexadehydrotribenzo[12]annulene. The backbone and its fluorinated analogue were synthesised in one-pot syntheses, with alkyne deprotection and Sonogashira cross coupling reaction being carried out in one step. Hydrosilylation of the annulene with chlorohydrosilanes proceeded highly selectively and afforded rigid poly-Lewis acids with three SiCl3 or SiCl2 Me substituents perfectly oriented to one side of the molecule in a single step. The progress of hydrosilylation was investigated by time-correlated NMR spectroscopic studies. The crystal structures show that the framework is symmetrically functionalised and the silyl substituents are aligned in one direction. To increase the acidity of the Lewis acids the chlorosilyl substituents were fluorinated with SbF3 . Further investigation of hydrometallation reactions (M=B, Al, Ga, Sn) did not lead to corresponding structures.

Synthesis of a Macrocycle Bearing a Carbon Framework of [16]Cyclophenacene as a Carbon Nanobelt

A synthetic pathway to a functionalized tetrahydro[5]phenacene was developed, which served as a precursor, leading to a dehydrobenzo[32]annulene macrocycle containing four carbon-carbon triple bonds. The high efficiency of the macrocyclization step can be attributed to the structural rigidity of its immediate precursor. Hydrogenation of the four carbon-carbon triple bonds produced a macrocycle bearing a carbon framework of [16]cyclophenacene as the shortest macrocyclic belt-like structure of an (8,8)armchair carbon nanotube.

Trifunctional organometallic frameworks and cages based on all-cis-1,3,5-triethynyl-1,3,5-trisilacyclohexanes

All-cis-1,3,5-triethynyl-1,3,5-triorganyl-1,3,5-trisilacyclohexanes (organyl R = Me, Ph) offer flexible scaffolds with three concordantly oriented ethynyl groups. Lithiation with n-BuLi affords the dimeric {[CH2Si(R)(C2Li)]3(THF)3}2 with a drum-like structure in high yields. They can be transformed into other trinuclear organometallic derivatives like the trimercury cage species [CH2Si(R)C2HgC2(R)SiCH2]3.

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.

Bi- and tridentate silicon-based acceptor molecules

Triethynylphenylsilane (1), trivinylphenylsilane (2), diethynyldiphenylsilane (3) and diphenyldivinylsilane (4) were reacted with chlorodimethylsilane yielding the corresponding hydrosilylation products. To increase their Lewis acidity, the Si–Cl functions were directly transferred into Si–C6F5 units by salt elimination reactions leading to the (semi-) flexible molecules 5–8 bearing two or three Lewis-acidic sidearms. With the aim of providing host-guest complexes, the air-stable and readily soluble compounds 5–8 were converted with N- and O-Lewis bases of different size and geometry. In all cases, NMR spectroscopic investigations reveal no formation of Lewis acid-base complexes. X-ray diffraction experiments of host compounds 5–7 show intermolecular aryl…perfluoroaryl interactions of dispersion nature in the solid state. By hydrosilylation of 1 with trichlorosilane the more Lewis-acidic all-trans-tris[(trichlorosilyl)vinyl]phenylsilane (9) was obtained. Its Lewis acidity was further increased by fluorination to yield all-trans-tris[(trifluorosilyl)vinyl]phenylsilane (10); the conversion with nitrogen containing Lewis bases ends up in the formation of insoluble precipitates.