A Striking Mode of Activation of Carbon Disulfide with a Cooperative Bis(silylene)

Abstract The reactivity of the 1,4‐substituted bis(silylenyl)terphenylene 1, 1,4‐[ortho‐(LSi)C6H4]2C6H4, (L=RC(NtBu)2, R=Ph, Mes) towards CS2 is reported. It results in a dearomatization of the phenylene ring, affording the 1,3‐substituted cyclohexadiene derivative 2. According to DFT calculations, a transient silene containing a Si=C bond capable of π(C=C) addition at the aromatic phenylene ring is a key intermediate. In contrast, addition of CS2 to the biphenyl‐substituted mono‐silylene ortho‐(LSi)C6H4‐C6H5 3 leaves the aromatic π‐system intact and forms, in a [1+2] cycloaddition reaction, the corresponding thiasilirane 4 with a three‐membered SiSC ring. Further experimental studies led to the isolation of the novel mesoionic five‐membered Si2S2C heterocycle 6, which reacts with CS2 under C−C bond formation. All isolated new compounds were fully characterized and their molecular structures determined by single‐crystal X‐ray diffraction analyses.


Molecule Index of new Compounds:
Single crystal X-ray structure analyses: Crystals were mounted on a glas capillary in perfluorinated oil and measured in a cold N2 flow. The data for all compounds were collected on an Agilent Technologies SuperNova device (single source) at 150 K (Cu-Kα radiation, λ = 1.54184 Å). All structures were solved by direct methods and refined on F 2 with the SHELX-97 software. [6] All atoms except for hydrogen atoms were calculated and considered isotopically according to a riding model.

Compound S1
To a suspension of mesityl lithium (8.00 g, 63.5 mmol, 1.0 equiv.) in Et2O (200 ml) N, 10.0 g, 64.8 mmol, 1.0 equiv.) was added at -78 °C. After warming up to room temperature, the reaction was stirred for 3 h. The suspension was added to a solution of trichlorosilane (9.80 ml, 13.2 g, 97.1 mmol, 1.5 equiv) in Et2O (50 ml) at -78 °C. The mixture was warmed up to room temperature and stirred overnight. The solution was filtered and concentrated and then kept at at -30 °C overnight affording S1 as colorless crystals suitable for X-ray diffraction analysis. After removal of Et2O by filtration, compound S1 was obtained in 51 % (12.0 g, 32.1 mmol) isolated yields. Compound S1 is not air stable and generally good soluble in organic solvents except for n hexane.

Synthesis of compound S2
A mixture of S1 (12 g, 32.1 mmol, 1.0 equiv.) and LiHMDS•Et2O (7.80 g, 32.1 mmol, 1.0 equiv.) was dissolved in cold Et2O (200 ml) and cooled to -78 °C. After warming up to room temperature, the mixture was stirred for 1 h turning from yellow to orange.
After the solution was filtered and concentrated under reduced pressure, the solution was kept at -30 °C overnight affording S2 as colorless crystals. Et2O was removed by filtration and the title compound S2 was obtained in 75 % (8.5 g, 32.4 mmol) isolated yields. Single crystals suitable for X-ray diffraction analysis of S2 were obtained from a concentrated solution in Et2O at -30 °C. Compound S2 is not air stable and generally good soluble in organic solvents except for n hexane.

Compound 3
To a suspension of 2-bromobiphenyl (212 µl, 1.23 mmol, 1.0 equiv.) and Et2O (5 ml) at -78 °C n Buli (615 µl, 2.0 M solution in THF, 1.23 mmol, 1.0 equiv.) was added via syringe. After stirring for 30 min at room temperature, all volatiles were removed under reduced pressure. The residue was re-dissolved in Et2O (5 ml) and added to a solution of N, N′-di-tert-butyl(mesitylamidinato) chlorosilylene S2 in Et2O (10 ml) at -78 °C. After stirring for 1 hour at room temperature, the solution was filtered and Et2O was slowly removed under reduced pressure without heating. The title compound 3 was obtained quantitatively (598 mg, 1.23 mmol) and was isolated as a crystalline orange solid.
Single crystals suitable for X-ray diffraction analysis of 3 were obtained from a concentrated solution of 3 in Et2O at -30 °C. Compound 3 is not stable in solution and slowly reacts to a silane via an intramolecular C-H activation reaction. Do not heat during work-up. 3 is stable in the solid state under an inert atmosphere for months.

Compound 9 (trithia-silabicyclo[3.2.0]-dithione)
To a solution of dithiasilolane 6 (40.0 mg, 0.045 mmol, 1.0 equiv.) in toluene (2 ml) an excess of CS2 was added dropwise at room temperature. After stirring for 30 min at room temperature the pink solution was filtered and concentrated under reduced 13 pressure. Single crystals suitable for X-ray diffraction analysis of 9 were obtained from a concentrated solution of 9 in toluene at -30 °C after one week. The isolated crystals of compound 9 were found to be completely insoluble in common organic solvents (benzene, toluene). Compound 9 could only be isolated in very small quantities.

Compound 10
In a Y. Young NMR tube 4 (10.0 mg, 0,019 mmol, 1.0 equiv.) was dissolved in C6D6 (0.5 ml) and heated to 50 °C for 4 h. The color of the solution changed with increasing conversion from red to dark brown. After removal of the solvent under reduced pressure, the residue was re-dissolved in Et2O (1.0 ml). The solution was filtered and transferred to a 5 ml Schlenk tube. The solvent was reduced to a volume of 0.2 ml upon which a dark red solution was obtained. Single crystals suitable for X-ray diffraction analysis of 10 were obtained after one week at -30 °C as colorless blocks.
The conversion of thiasilirane 4 to silathione 10 is quantitative as observed by 1
15 Figure S2. 13 C{ 1 H} NMR spectrum of compound S1 in C6D6 under 1 bar N2 at 298 K.                      All quantum chemical calculations were carried out using Gaussian 09. [7] The geometries of all compounds were optimized at B3LYP [8] -D3 [9] /def2-SVP [10] basis set for all other atoms. Analytical frequencies were computed to verify the stationary points. Thermochemistry at 298.15 K.