Frustrated Lewis pairs (FLPs) have a great potential for activation of small molecules. Most known FLP systems are based on boron or aluminum atoms as acid functions, few on zinc, and only two on boron-isoelectronic silicenium cation systems. The first FLP system based on a neutral silane, (C2F5)3SiCH2P(tBu)2 (1), was prepared from (C2F5)3SiCl with C2F5 groups of very high electronegativity and LiCH2P(tBu)2. 1 is capable of cleaving hydrogen, and adds CO2 and SO2. Hydrogen splitting was confirmed by H/D scrambling reactions. The structures of 1, its CO2 and SO2 adducts, and a decomposition product with CO2 were elucidated by X-ray diffraction.

Chlorogermane (C2F5)3GeCl with very electronegative pentafluoroethyl groups was converted with LiCH2P(tBu)2 to obtain the intramolecular frustrated Lewis pair (FLP) (C2F5)3GeCH2P(tBu)2, a neutral, germanium‐based FLP. Its reactivity was compared to its silicon homologue (C2F5)3SiCH2P(tBu)2. Both FLPs cleave NO but give cyclic (Si) and open‐chain oxides (Ge). In reactions with HCl both FLPs gave the same adduct type in the solid state, while the proton seems more mobile in solution in the germanium case. Reactions with PhCNO and Me3SiCHN2 result in ring‐type adducts. The structures of (C2F5)3GeCH2P(tBu)2 and of five adducts with substrates were elucidated by X‐ray diffraction. The study clearly showed the germanium compound to have a more moderate Lewis acidity compared to the silicon analogue.

Abstract1,8‐Dichloroanthracenes bearing EMe3 substituents at the 10‐position (E = Si, Ge, Sn) have been synthesised by salt elimination reactions. The key compound, 10‐bromo‐1,8‐dichloroanthracene (2), was quantitatively obtained by conversion of 1,8‐dichloroanthracene with elemental bromine in dichloromethane. The EMe3‐substituted anthracene compounds 1,8‐dichloro‐10‐(trimethylsilyl)‐ (3), 1,8‐dichloro‐10‐(trimethylgermyl)‐ (4) and 1,8‐dichloro‐10‐(trimethylstannyl)anthracene (5) were completely characterised by multinuclear NMR spectroscopy and mass spectrometry. Their molecular structures in the crystalline state were analysed by X‐ray diffraction experiments and compared with the crystal structure of 10‐tert‐butyl‐1,8‐dichloroanthracene (1). It was found that the level of deformation of the anthracene backbone continuously increases along the series of anthracene substituents SnMe3 < GeMe3 < SiMe3 < CMe3. Owing to the good agreement of experimental structural parameters with the results of quantum chemical calculations, the molecular deformations can be regarded as inherent molecular properties.

Two new silicon/phosphorus-based frustrated Lewis pairs (FLP), F 3 SiCH 2 PtBu 2 (1) and Cl 3 SiCH 2 PtBu 2 (2) were prepared from lithiated di-tert-butylmethylphosphane, LiCH 2 PtBu 2 , and the corresponding silicon tetrahalides. They were characterised by NMR spectroscopy and by single-crystal X-ray diffraction. A gas phase electron diffraction study of 1 identified two conformers of similar energy in the vapor. The reactivity of both, 1 and 2, towards a series of small molecules was investi-

[2] wurden die vielfältigen Mçglich-keiten, die das Konzept erçffnet, erst seit kurzem erkannt und erschlossen. Stephan und Mitarbeiter entdeckten das Vermçgen von FLPs,W asserstoff reversibel zu spalten, zu speichern und wieder freizusetzen [3] oder ihn auf reduzierbare Substrate zu übertragen.