Silylenes dichloro

Again dismissing semi-empirical and STO-3G models, calculations and experiment are in close accord with regard to bond angles in silylene (near to 90°) and its difluoro and dichloro analogues (near to 100°). 

Kummer and Koster62 were the first to mention a silylene complex in organometallic synthesis. Treatment of hexachlorodisilane with 2,2 -bipyridyl resulted in a stable 1 2 adduct, which was interpreted as a dichloro-silylene coordinated to two bipyridyl molecules. However, because of the restricted possibilities at that time, no further experimental or spectroscopic... 

The reaction of Si-dichloro substituted silacyclobutenes and -butanes with metal fragments yield stable silylene complexes no ring cleavage is observed - Silacyclobutenes N. Auner, C. Wagner, E. Herdtweck, M. Heckel, W. Hiller, Bull. Soc. Chim. Fr., in press. - Silacyclobutanes N. Auner, M. Grasmann, B. Herrschaft, P. Kiprof, J. Organomet. Chem., in press ... 

The h NMR spectrum provides some evidence for aromatic stabilization in 5. The important number is the chemical shift for the ring C-H protons, which falls at 6.75 ppm. This is significantly deshielded compared with the same protons in the precursor 4, 5.73 ppm, or the corresponding dihydride (LSiH2), 6.00 ppm. Theoretical calculations also support the idea that 5 is an aromatic molecule, with aromatic resonance energy of 12 s kcal mol . Particularly convincing, however, is a comparison of the properties of 5 with those of its saturated analog [22]. Silylene 13 was made by a reaction sequence similar to that for 5 in Eq. 4 and Eq. 5, except that for the final step it was necessary to use the dibromo rather than the dichloro compound (Eq. 13). For 13 an X-ray crystal structure could be determined it is shown in Fig. 5. 

The formation of silylenes and silaethenes by dehalogenation of dichloro- and chloromethyl-chlorosilanes was previously described using the reaction of Na/K vapor in the gas-phase at 300 °C [1]. In the presence of butadiene the reaction with RR SiCl2 leads to silacyclopentenes. 

Summary The stable silylene 1 reacts with halocarbons like dichloro-, trichloro-, and tetrachloromethane at room temperature under formation of the disilane 3. The mechanism of this reaction is still unknown. Results of recent ab initio calculations do not agree with the experimental observations. In this investigation we have studied the photochemical behavior of the stable silylene 1 in a diluted ai]gon-tetrachloromethane matrix at 10 K as well as the thermal properties of 1 in pure solid CCU in the temperature range of 10 - 200 K. The formation of a trichloromethyl radical in both types of experiments indicates that electron transfer may play an important role in these processes. 

The reaction of the stable silylene 1 with halocarbons (Scheme 1) was first observed by West and coworkers [2], With tert-butyl chloride the expected insertion product 2 is formed. In the case of halocarbons like dichloro-, trichloro-, or tetrachloromethane, surprising results were obtained. Two silylene molecules and one halocarbon molecule combine very rapidly at room temperature yielding disilane 3. With bromobenzene both reaction products 4 and 5 are generated in a slow... 

The dichloro compound was first generated upon photolysis of dichlorosilane by Milligan and Jacox . In addition, all dihalosilylenes except of the diiodo compound are accessible from the reaction of the respective silicon tetrahalide with silicon at high temperatures . A more recent approach to a halogen substituted silylene is the cocondensation of hydrogen fluoride with silicon atoms, yielding fluorosilylene . 

Theoretical study of cycloadditions of formaldehyde with cyclopropyhdene, dimethyl-silylene carbene, and dichloro-germylene carbene has been conducted at MP2/6-311-t-G and MP2/6-31G levels of theory two competitive dominant pathways have been identified in each case. Likewise four competitive dominant pathways have been found for reaction of dichlorogermylene silylene and acetaldehyde. ... 

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