Metallodendrimers Unveiled: Investigating the Formation and Features of Double-Decker Silsesquioxane-Based Silylferrocene Dendrimers

Dendrimers exhibiting reversible redox properties have attracted extensive attention for their potential as electron transfer mediators, catalysts, and molecular sensors. In this study, we introduce intriguing G1 and G2 dendrimers featuring double-decker silsesquioxane cores and silylferrocene moieties. Through a carefully orchestrated sequence of condensation, reduction, and hydrosilylation reactions, these compounds were synthesized and comprehensively characterized spectroscopically and spectrometrically. Our investigation also encompassed the examination of their properties, including thermal stability, solubility in common organic solvents, and electrochemical behavior. We determined that these dendrimers possess the capability to form monolayers on platinum electrodes, which we conclusively demonstrated through the probing of cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy imaging. Notably, this study marks the first-ever example of modifying double-decker silsesquioxane cores with ferrocene groups while simultaneously representing one of the scarce instances of dendrimers exhibiting an open double-decker silsesquioxane core.

From Bidentate Gallium Lewis Acids to Supramolecular Complexes

Bidentate gallium Lewis acids were prepared by the reaction of diethynyldiphenylsilane with neat trimethyl- or triethylgallium. Bis[(dimethylgallyl)ethynyl]diphenylsilane (1) and diethylgallyl derivative 2 were characterized as Et₂ O or pyridine adducts by NMR spectroscopy; 2⋅2Py was isolated. Lewis acids 1 and 2 form host-guest adducts with bidentate nitrogen bases, but defined cyclic 1:1 adducts are only formed between 1 and bases with matching N⋅⋅⋅N distances: 4,4'-dimethyl-3,3'-bipyridinylacetylene (3), bis[(pyridin-3-yl)ethynyl]diphenylsilane (4), and bis[(2-methylpyridin-5-yl)ethynyl]diphenylsilane (5). The structures of adducts 1⋅3, 1⋅4, and 1⋅5 were established by X-ray diffraction experiments. 2⋅2Py reacts with DABCO to afford polymeric (DABCO-2-)_n .

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.

Fluoride complexation by bidentate silicon Lewis acids

The fluoride ion complexation behavior of the bidentate open-chain Lewis acids Ph₂Si(CHCHSiF_nMe_3−n)₂and Ph₂Si(CH₂–CH₂SiF_nMe_3−n)₂(n= 1, 2, 3) was explored in detail by multinuclear low-temperature NMR spectroscopy in solution and by X-ray diffraction experiments.