Dichlorosilylene

The chemistry of dichlorosilylene can be studied by either gas-phase or cocondensation reactions (17, 62, 103, 104). In most cases, dichlorosilylene generated by pyrolysis of perchloropolysilanes was used in the gas-phase reactions whereas thermal reduction was used for cocondensation experiments. 

As in the case of SiH2 chemistry, dichlorosilylene has been found to undergo mainly two types of reactions, namely, insertions and additions according to the types of reaction products formed. 

Dichlorosilylene also inserts into halogens, hydrogen chloride, and the hydrogen molecule  

It is particularly interesting to note that at elevated temperatures some of the products from SiCl2 insertion into C—H and Si—H bonds would undergo hydrogen elimination on cyclization (10, 24, 119), for example, Eqs. (19) and (20). 

In cases where the cyclization process mentioned above produced strained rings, further SiCl2 insertion into the rings was observed. This is best illustrated by comparing the two reactions shown [Eq. (21) vs. Eq. (22)] (9,18, 21, 22)  

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An example of particular interest is the two-fold introduction of M(CO)n moieties at silicon to give HMPA adducts of organometallic analogues of silaallene. It has been shown that this reaction proceeds through the dichlorosilylene complex as intermediate. Both the iron 22 and ruthenium 23 compound and also the bimetallic complex 24 are accessible. 

Stable silylene complexes with halogen substituents are a useful starting material for further displacement reactions. Starting from 7 and 11, the Si complexes 22-24 are accessible in high yield. However, the intermediate dichlorosilylene complex... 

The combination of carbonylate dianions with silicon tetrachloride leads in high yields to the p-Si compounds 22-24. As already mentioned, the reaction can be performed either stepwise with isolation of the dichlorosilylene complex or in a one-pot procedure. The resulting products show a surprisingly high thermal... 

The bands of the SiCls radical (Milligan and Jacox, 1968b), have not been observed at all. Due to the high selectivity of its thermal decomposition within a wide temperature interval, Si2Cl6 has become one of the most suitable precursors of dichlorosilylene in preparative chemistry (Chernyshev and Komalenkova, 1990). 

Dichlorodisulfane, UV spectrum of, 16 311 a,w-Dichloro-oligosilane, 42 221 Dichlorofprotoporphyrin IX)tin(IV), 36 14-15 Dichlorosilylene, 29 6-15 action reactions, 29 12-15 with alkynes, 29 12-13 with conjugated dienes, 29 13... 

With dichlorosilylene, similar products result along with smaller amounts of the 2-silaindane. These are thought to result from insertion, or addition, of the silylene to the bicyclo valence isomer (11) of cyclooctatetraene (Scheme 24) (75ZOB2221), although a similar route to that in Scheme 23 is also possible. 

Inorganic Silylenes. Chemistry of Silylene, Dichlorosilylene, and Difluorosilylene... 

Dichlorosilylene and dichlorogermylene are formed in the gas phase at 500-550 °C and can be trapped with 1,3-butadienes with the formation of substituted l,l-dichloro-2,5-dihydrometalloles 154 <2001RJC1438>. 

INORGANIC SILYLENES. CHEMISTRY OF SILYLENE, DICHLOROSILYLENE, AND DIFLUOROSILYLENE... 

Since data for the mechanistic details, such as the spin states and initial attacking site of the insertion of dichlorosilylene is lacking, inferences about the nature of the insertion reactions are at best a straightforward assumption based on the molecular structure of the final products. However, the insertion reactions of SiCl2 into C—X bonds, which proceed through elimination-recombination steps, do resemble the chemistry of singlet carbenes (59). It seems reasonably safe... 

Some Insertion Reactions of Dichlorosilylene into C—X Bonds Reactant Product... 

Under cocondensation conditions, propene was reported to react with dichlorosilylene to form tetrachloro-l,4-disilacyclohexane derivatives (96, 103). 

The reaction mechanism for dimerization of the silirene intermediate has been a controversial subject for many years 3, 4, 7, 45, 49, 58, 86). It is now generally accepted that in the case of dialkylsilylene, (T-dimerization is probably the true mechanism. Dichlorosilylene is expected to behave similarly. 

The reaction of dichlorosilylene with acetylene carried out by a cocondensation experiment also yielded l,4-disilacyclohexa-2,5-diene, but the result was regarded as unreliable 103,104). 

Studies on the gas-phase reactions of dichlorosilylene with conjugated dienes provided more systematic information about the addition reactions of dichlorosilylene (1,10,15,16, 20, 30, 91) ... 

Above 500°C dichlorosilacyclopent-3-ene can be converted to disila-cycles in the absence of trapping agent. The dichlorosilylene, formed... 

In view of the well-established silirane diradical mechanism in reactions of silylene [Eq. (10)] and dimethylsilylene 40, 62), and the involvement of difluorosilirane in the gas-phase reaction of difluoro-silylene [Eq. (61), Section IV], it is somewhat surprising to find that dichlorosilylene alone should take a concerted 1,4-addition route toward butadiene. Further studies are needed to settle this argument. 

The gas-phase reaction of dichlorosilylene with cyclopentadiene yielded silacyclohexadienes as the major products, one of which underwent further SiCl2 insertion to form a bicyclic product 31). 

Summary Starting with poiy(dichlorosilyiene-co-methylene) the synthesis of new poly(di-alky silylene-co-methylenes), poly(dialkenylsilylene-co-methylenes), and poly(dialkinylsilyl-ene-co-methylenes) was achieved by Grignaid or organolithium reactions. Furthermore poly(dichlorosilylene-co-methylene) was photochlorinated under UV irradiation to poly-(dichlorosilylene-co-dichloromethylene). 

The substitution of the phenyl groups by HCl imder the catalytic influence of the Lewis acid AICI3 led to poly(dichlorosilylene-co-methylene) [3]. 

Poly(dichlorosilylene-co-dichloromethylene) could be converted by reactions of organo-lithium compounds into peralkylated poly(carbosilanes) according to ... 

Dichlorosilylene may be prepared by pyrolysis of perchloropolysilanes and again nndergoes both insertion and addition reactions. The insertion into a wide variety of bonds, including C-H bonds, has been studied (Scheme 7). At the elevated temperatures used in these reactions, elimination of H2 and cyclization may also occur and, if the ring formed is strained, a further Cl2Si insertion may occur. 

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