Bis(trimethylsilyl)acetylene

Four-Electron Oxidative Addition of an N=N Double Bond at a Chromium Metallocyclopropene

This report describes the synthesis of a pseudo-tetrahedral chromium alkyne complex supported by a bidentate phosphinimide ligand and its reactivity with an azobenzene derivative. Characterization of the former by structural and computational methods reveals an unprecedented extent of alkyne activation by a formal chromium(II) center, suggesting that this complex is best described as a chromium(IV)-metallocyclopropene. Exposure of this compound to 4,4'-difluoroazobenzene results in the formation of a chromium(VI) diimido complex, which constitutes a rare 4-electron oxidative addition of an N=N double bond. The isolation of a chromium(IV)-hydrazido intermediate enabled mechanistic investigations of this challenging bond cleavage process. This work substantiates the notion that terminal phosphinimide ligands can engender first-row transition metal ions with exceptional reactivity.

π-Conjugated species with an unsupported Si-Si π-bond obtained from direct π-extension

1,3-Diethynylbicyclo[1.1.0]tetrasilanes that contain an unsupported bridgehead Si-Si π-bond and ethynyl π-moieties were synthesized by the reaction of a 1,3-dihalobicyclo[1.1.0]tetrasilane with the corresponding lithium acetylide. The substantial bathochromic shift of the longest-wavelength absorption band observed for the phenylethynyl-substituted bicyclo[1.1.0]tetrasilane in the solid state compared to that of the octynyl-substituted derivative suggested the presence of effective π-conjugation between the unsupported Si-Si π and ethynyl π units.

Synthesis of a titanium ethylene complex via C–H-activation and alternative access to Cp2Ti(η2-Me3SiC2SiMe3)

The synthesis of a room temperature stable titanacyclopropane in a one-step-two-transformation protocol is presented. Additionally, a novel one-pot procedure toward Cp₂Ti(η²-Me₃SiC₂SiMe₃) was subsequently developed.

Titanocene Silylpropyne Complexes: Promising Intermediates en route to a Four-Membered 1-Metallacyclobuta-2,3-diene?

Coordination of the alkyl-substituted alkynes Me₃ SiC₂ CH₂ R (1: R=SiMe₃ ; 2: R=N(SiMe₃ )₂ ) to titanocene centres [Cp'₂ Ti] (Cp'=Cp, Cp*) yields stable alkyne complexes of the type Cp'₂ Ti(η² -Me₃ SiC₂ CH₂ R) (3: Cp'=Cp, R=SiMe₃ ; 5: Cp'=Cp, R=N(SiMe₃ )₂ ; 6: Cp'=Cp*, R=SiMe₃ ) that are not prone to alkyne/allene isomerisation. When reacting alkyne 2 with Cp^*₂ TiCl₂ and Mg formation of the complex Cp*₂ Ti(III)(η³ -Me₃ SiC₂ CH₂ ) (7) which displays a propargylic unit coordinated to the Ti^III centre takes place. All complexes were fully characterised, the molecular structures for 5, 6, and 7 are discussed.

(Butane-1,3-diyne-1,4-diyl)bis-(tri-isopropyl-silane)

The mol-ecule of the title compound, C(22)H(42)Si(2), lies on a center of inversion, and the triisopropyl-silyl groups are staggered.

1,2-Dialkynyldisilenes: silicon analogues of (E)-enediyne

Reductions of bulky alkynyl-substituted dihalosilanes, BbtSiX(2)(C[triple bond]CR) (Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl, R = SiMe(3) or Ph groups, X = halogen), with 2.0 equiv. of lithium naphthalenide gave the first stable 1,2-dialkynyl-substituted disilenes, which constituted extended pi-conjugated systems between Si=Si bond and ethynylene units.