Regiospecific C–H Bond Activation: Reactivity Study of N-Heterocyclic Silylene toward Ambidentate Phosphorus Ylide

Facile Conversion of Bis-Silylene to Cyclic Silylene Isomers: Unexpected C-N and C-H Bond Cleavage

Reaction of thiolate 1 with carbene-stabilized diiodo-bis-silylene (2) (in a 2:1 ratio) in THF unexpectedly gives both the first five-membered, sulfur-containing, zwitterionic silylene ring (3) via insertion of the "Si^I₂" unit of 2 into the olefinic C-H bond of the imidazole ring of 1 and four-membered cyclic silylene (4) via insertion of a silicon(I) atom of 2 into the C_phenyl-N bond of the carbene ligand. The parallel reaction in toluene only gives 3 as the major product. The nature of the bonding in isomeric 3 and 4 was probed by experimental and theoretical methods.

Mixed valence η6-arene cobalt(I) and cobalt(II) compound

The first carbonyl free mixed valence cobalt(I)/cobalt(II) compound [2{L2Co(I)(η(6)-C7H8)}](2+) [Co(II)2Cl6](2-) (1) [L = PhC(N(t)Bu)2SiCl] was obtained by the reaction of four equivalents of anhydrous CoCl2 with five equivalents of N-heterocyclic chlorosilylene L. In contrast, the reaction of L with CoBr2 yielded [L2CoBr2] (2). Compound 1 was formed by the cleavage of Co-Cl bonds, the reduction of Co(II) to Co(I) and by the coordination of a toluene molecule. The chlorosilylene (L) functions as a reducing agent as well as a neutral σ-donor ligand. The toluene molecule coordinates to the Co(I) atom in an η(6)-fashion.

Reaction of N-heterocyclic silylenes with thioketone: formation of silicon-sulfur three (Si-C-S)- and five (Si-C-C-C-S)-membered ring systems

Three- and five-membered rings that bear the (Si-C-S) and (Si-C-C-C-S) unit have been synthesized by the reactions of LSiCl (1; L=PhC(NtBu)2 ) and L'Si (2; L'=CH{(CCH2 )(CMe)(2,6-iPr2 C6 H3 N)2 }) with the thioketone 4,4'-bis(dimethylamino)thiobenzophenone. Treatment of 4,4'-bis(dimethylamino)thiobenzophenone with LSiCl at room temperature furnished the [1+2]-cycloaddition product silathiacyclopropane 3. However, reaction of 4,4'-bis(dimethylamino)thiobenzophenone with L'Si at low temperature afforded a [1+4]-cycloaddition to yield the five-membered ring product 4. Compounds 3 and 4 were characterized by NMR spectroscopy, EIMS, and elemental analysis. The molecular structures of 3 and 4 were unambiguously established by single-crystal X-ray structural analysis. The room-temperature reaction of 4,4'-bis(dimethylamino)thiobenzophenone with L'Si resulted in products 4 and 5, in which 4 is the dearomatized product and 5 is formed under the 1,3-migration of a hydrogen atom from the aromatic phenyl ring to the carbon atom of the CS unit. Furthermore, the optimized structures of probable products were investigated by using DFT calculations.