Correspondence silacyclopropene

In the reaction of 1 with alkynes possessing electron-withdrawing substituents, the corresponding silacyclopropene derivatives 66 and 67 are formed, as described in Scheme 23.29 An unexpected pathway was observed in the reaction with the electron-poor hexafluorobutyne(2) the X-ray characterized heterocycle 68 was most likely obtained by nucleophilic attack of 1 at the triple bond. A subsequent shift of a fluorine atom from carbon to silicon creates an allene-type molecule which was stabilized by a [2 + 2] cycloaddition process involving a double bond from the pentamethylcyclopentadienyl unit, as described in Scheme 24.33... 

Applying a unique method for the synthesis of 1,1 -dilithiosilanes 78 from the corresponding silacyclopropenes 77,12 a convenient synthetic route to A2Si = SiB2-... 

The first synthesis of unsubstituted silacyclopropene 8 was achieved recently, along with a novel route to obtain this class of substances. High vacuum pyrolysis of l,l,l-trimethyl-2-vinyldisilane 80 produces the corresponding silacyclopropene by elimination of trimethylsilane (Scheme 23). A ring-opening reaction of the silacyclopropene produces the other product <1995AGE1439>. 

Co-thermolysis of pivaloyl-adamantoly(trimethylsilyl)-silanes with disubstituted acetylenes was carried out in a sealed glass tube, at 160 °C for 12 h, producing the corresponding silacyclopropenes 85 in high yields (R = /-Bu, Adamantyl R = phenyl R = Me, Ph) (Equation 20) <20000M4921>. The products were characterized by Si-NMR spectroscopy. 

Reductive dehalogenation of highly coordinated dichlorosilanes with magnesium yield cyclotrisilane 96, which is in equilibrium with silylene and can be used as a versatile synthetic equivalent for this silylene. It was quantitatively converted to the corresponding silacyclopropene 97 by treatment with an excess of trimethylsilylacetylene (Scheme 30) <1998CEJ852>. 

Irradiation of tris(trimethylsilyl)phenylsilane in the presence of hex-l-yne and other alkynes affords the corresponding silacyclopropenes. Those silacyclopropenes formed from monosubstituted acetylenes undergo further photoisomerization to disilanylacetylenes via a 1,2-hydrogen shift. Two competing pathways have been observed on irradiation of the disilabicyclo[2.2.2]octa-2,5-diene... 

Tetramethylsilacyclopropene, the first silacyclopropene derivative, was prepared in 1976145. With the help of the matrix-isolation techniques, attempts were made to synthesize the parent silacyclopropene (114). Experiments with this goal culminated in the isolation of 1, 1 -dimethylsilacyclopropene (110) in solid argon146. Sander and coworkers showed that 110 is accessible by photolysis of the corresponding bis(diazomethyl)silane (109) (equation 29). After subsequent irradiation with shorter wavelengths, isomerization into the photostable ethynyldimethylsilane (111) takes place. 

Monitoring the reaction by 111-NMR spectroscopy clearly indicates the formation of the 1,2-disilacyclobutenes by a two-step addition-insertion process. Primarily, the silylene generated by thermal decomposition of the cyclotrisilane adds to the C—C triple bond yielding the silacyclopropene. Further insertion of a second silylene into the Si—C bond of the silacyclopropene finally affords the corresponding 1,2-disilacyclobutene. 

A bis(silacyclopropene) 47 was converted to the corresponding disilabenzvalene 48 by heating or by treating 47 with AgBF4 (equation 40). The following pathway involving a... 

Silylium ions stabilized by Si-X-Si three-center bonds (X = halogen or hydrogen) have been synthesized by the reaction of the corresponding l-tris(trimethylsilyl)methyl-2,3-bis(trimethylsilyl)-l-silacyclopropene derivative with triethylsilylbenzenium tetrakis(pentaflourophenyl)borate <2004CL530>. 

An analysis of the dimerization of silacyclopropene was carried out by Orbital Correspondence Analysis in Maximum Symmetry (OCAMS). This analysis showed that the dimerization of silacyclopropene follows an allowed pathway <82JOM(240)129>. 

Insertion of diarylsilylene (58) into three different silacyclopropenes gave the corresponding 1,2-disilacyclobutenes in quantitative yield (Scheme 21) <94CC1989>. Diarylsilylene (58) was generated in situ by thermolysis of a cyclotrisilane under mild conditions. 

Figure 7.14. Correspondence diagram for dimerization of Silacyclopropene (D2/1). (The asymmetry introduced by the substitutents is ignored)...

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