Twofold Hydrogallation of C⋮C Triple Bonds by H−GaCl2Synthesis of Chelating Lewis Acids and Their Application in Adduct Formation

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.

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.

Gallium Hydrides with a Radical-Anionic Ligand

The reaction of Cl₂GaH with a sodium salt of the dpp-Bian radical-anion (dpp-Bian^•-)Na (dpp-Bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) affords paramagnetic gallane (dpp-Bian^•-)Ga(Cl)H (1). Oxidation of (dpp-Bian^2-)Ga-Ga(dpp-Bian^2-) (2) with N₂O results in the dimeric oxide (dpp-Bian^•-)Ga(μ²-O)₂Ga(dpp-Bian^•-) (3). A treatment of the oxide 3 with phenylsilane affords paramagnetic gallium hydrides (dpp-Bian^•-)GaH₂ (4) and (dpp-Bian^•-)Ga{OSi(Ph)H₂}H (5) depending on the reagent's stoichiometry. The reaction of digallane 2 with benzaldehyde produces pinacolate (dpp-Bian^•-)Ga(O₂C₂H₂Ph₂) (6). In the presence of PhSiH₃, the reaction between digallane 2 and benzaldehyde (2: PhSiH₃: PhC(H)O = 1:4:4) affords compound 4. The newly prepared complexes 1, 3-6 consist of a spin-labeled diimine ligand-dpp-Bian radical-anion. The presence of the ligand-localized unpaired electron allows the use of the ESR spectroscopy for characterization of the gallium hydrides reported. The molecular structures of compounds 1, 3-6 have been determined by the single-crystal X-ray analysis.

Tridentate Lewis-acids based on triphenylsilane

Triphenylsilanes are versatile propeller-shaped building blocks and have been used for the syntheses of several novel poly-Lewis-acids. The first solid-state structure of a bisma-silatriptycene as well as investigations in host–guest chemistry of a triple alane with a threefold amine are reported.

Tridentate Lewis acids with phenyl substituted 1,3,5-trisilacyclohexane backbones

A new 1,3,5-trisilacyclohexane scaffold with axially orientated ethynyl groups provides opportunities to create new tridentate Lewis acids. Some examples of these Lewis acids have been synthesized.

Vinylgallium and alkyllithium compounds: transmetalation and generation of oligolithium cages

Vinylgallium compounds [C(6)H(6-n){(H)C=C(SiR(2) R')-GaR''(2)}(n ] (3, R=Ph, Me; R'=Ph, Me; R''=tBu, Et; n=1, 2) are easily accessible by hydrogallation of the corresponding alkynylbenzene derivatives with H-GaCl(2) and subsequent reaction with alkyllithium derivatives. Treatment of 3 with an excess amount of tert-butyl- or ethyllithium yielded by transmetalation and ortho-deprotonation of the aromatic rings the unprecedented solvent-free oligolithium cluster compounds [{(C(6)H(4)Li)HC=C(SiPh(3))Li}(2)(tBuLi)(2)] (4), [{(C(6)H(4)Li)HC=C(SiPh(2)Me)Li}(4)] (5) and [{(C(6)H(3)Li){HC=C(SiMe(3))Li}(2)}(3)] (6) in moderate yields. Their solid-state structures revealed the presence of unique molecular lithium clusters with 6, 8, or 9 lithium atoms that may be derived from two edge-sharing Li(4) tetrahedra (4), three Li(4) tetrahedra in a chain joined by two common edges (5) or a tricapped trigonal prism of lithium atoms (6).