Silacyclopropanes structure

The coordination compound 76 was stable enough for isolation and recording of its NMR spectra, from which a rigid silacyclopropane structure could be deduced. The mechanism of complex formation has also been investigated in detail by matrix techniques. 

The classical open /l-silylethyl cation 9 and /f-silylvinyl cation 11 are no minima at higher level of theory3,4. They collapse to the bridged protonated silacyclopropane 21 and silacyclopropene 22, respectively. On the basis of their calculated structures (Figure 3) both cyclic molecules are best described as -complexes between a silylium ion and ethene or acetylene, respectively. 

Ando and coworkers found that the silylene Dip2Si 382 (Dip = 2,6-di-/-propylphenyl), formed on photolysis of the trisilane 382 in the presence of Cgo, gave an adduct assigned the structure of the silacyclopropane 384 which evidently arose from addition of the silylene across the C=C between two six-membered rings of the fullerene198. A segment of the structure of 384 is shown in equation 47. 

Spectroscopically pure silacyclopropane 3a was formed quantitatively, when 1 was heated at 40 °C for 12 h with an excess of 1-pentene in CgDj. Especially the characteristic Si NMR shift values [6] (3a 8 = -76.6 ppm) proved the proposed cyclic structure. Isolation of analytically pure 3a from the reaction mixture was impossible due to its inherent thermal instability. Heating a concentrated solution of 3a in for 5.5 h at 40 °C resulted in a 1 1 3 mixture of 3a, 1, and 1-pentene. An analogous partial retro reaction to 1 and an olefin was also shown by silacyclopropane 3b, which was similarly synthesized by reaction of 1 with excess 1-hexene. 

Although x-ray diffraction remains the most reliable method for ascertaining the structures of three-membered rings with one silicon or tin, l3C NMR and 29Si NMR can be quite useful (Table 2). In silacyclopropanes, the chemical shifts for the ring carbons range from 10-23 ppm for silacyclopropenes, the range is 147-195 ppm. 

Silatrimethylenemethane iron complexes were synthesized by reaction of Z- and E-alkylidene silacyclopropanes (80) and (81) with Fe2(CO)9 (Equation (36)). Structure assignments were based on spectroscopic data as well as an x-ray crystal structure of the Z iron complex. 

Treatment of (80) and (81) with Ru3(CO)12 gave the >/4-silatrimethylenemethane-ruthenium complexes in 9% and 22% yield, respectively. The major product of the Z-alkylidenesilacyclopropane reaction was trinuclear ruthenium carbonyl cluster (82), whose structure was established by x-ray diffraction (Equation (37)). This appears to be the first example of a main group metal-bound carbonyl inserting into a silacyclopropane <9lJA279i, 94OM4606). 

Generation of dimethylsilylene from hexamethylsilacyclopropane in the presence of cis- and trans-4-octene, cyclooctene, propenyltrimethylsilane, and trimethylethylethene gave the corresponding silacyclopropanes. The yields of these reactions were determined by gas-liquid chromatography (GLC) and structures indicated by their methanolysis products (Scheme 28) <76JOM(ll7)C5l>. 

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