Regardless of the amount of selenium used, the dihydride 1 (Ar=2,6‐iPr2C6H3) reacts to afford 2. In solution, intermolecular elimination of H2Se takes place with formation of 3, which displays a bridging Al‐Se‐Al moiety. Compounds 2 and 3 are the first structurally characterized organometallic compounds which contain metal–SeH units.

Upon treatment of tribenzotriquinacene (4a) (R = H) and its centro-alkyl-substituted derivatives 4b-d (R = CH3, C2H5, CH2Ph) with the strongly basic mixture of n-BuLi and KOTen, 2-fold deprotonation combined with (formal) elimination of RH from positions C( l)-C(lO) occurs to generate tribenzacepentalene dianion 5-K2 with varying ease. Dianion 5-K2 can be trapped with various electrophiles to give 4,7-disubstituted tribenzodihydroacepentalenes 6c-f in good yields. Compounds 6a-f contain an extremely out-of-plane bent C( l)=C( 10) double bond, as shown by X-ray structure analyses of 6b-d, and therefore possess an increased reactivity. 4,7-Dihydrotribenzacepentalene (6a) obtained upon protonation of 5 at -78 "C dimerizes at higher temperatures (20 "C) toward the head-to-head [2 + 21 dimer 22. At elevated temperatures (1 220 "C), 22 is cleaved to regenerate 6a which can be trapped with anthracene and tetracyclone to give the highly condensed Diels-Alder adducts 23 and 24. Likewise, 6a generated from 5 at low temperatures can be trapped with 1,3-diphenylisobenzofuran, yielding 25. X-ray structure analyses of dimer 22 and adduct 23 revealed strongly elongated 1,1,2,2-tetraarylethane C-C bonds, which are attributed to through-bond n-o* couplings in these rigid frameworks. The 4,7-bis(trimethylstannyl)-tribenzodihydroacepentalene (60 undergoes clean transmetalation with methyllithium to give pure dilithium tribenzacepentalenediide (5-Li2.) Crystal structure analysis reveals that the dianionic fragments 5-Li2 in these solventseparated ion pairs are considerably curved.

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Abstract Depending on the solvent and the bulkiness of the substituents, Iithiated aminofluorosilanes are dimers, monomers, or LiF-adducts of iminosilanes. In the crystal structure of the dimeric lithium derivative of di-tert-butyl(rm-butylamino)fluorosilane, each lithium atom is coordinated by one fluorine and two nitrogen atoms. LiF-elimination leads - if sterically possible - to dimerisation. The limits of dimerisation are reached with the dimer diisopropyl(tri-tert-butylphenyI- imino)silane, for which the crystal structure analysis shows severe steric distortions. Fluorine- chlorine-cxchange occurs in reactions of lithiated (tri-tert-butylphenylimino)fluorosilanes with Me3SiCl. Iminosilanes are obtained by thermal LiCl-elimination from the resulting salts.

N,NЈ-Di-tert-butyl-1,4-diaza-1,3-butadiene reacts with elemental lithium under reduction to give a dilithium salt, which forms with fluorosilanes the diazasilacyclopentenes 1Ϫ4