Hetero-π-systems from 2+2 cycloreversions. Part 1. Gusel'nikov–Flowers route to silenes and origination of the chemistry of doubly bonded silicon

Hetero‐π‐systems from 2 + 2 cycloreversion, part 2.1Ab initio thermochemical study of heterocyclobutanes 2 + 2 cycloreversion to form heteroethenes H2C=X (X=NH, O, SiH2, PH, S)

“…The activation energies of oxetane's cycloreversion (62.6 and 63.1 kcal/mol via C C and C O bond cleavage, respectively [76]), are also close to the predicted ring-opening enthalpies, 60.7/60.2 and 64.7/60.2 kcal/mol. Taking into consideration the correction on the stabilization effects of silicon atom (see footnote to Table 12), our calculations predicted for siletane the initial cleavage of C C bond, a conclusion widely accepted in the literature [2,3,[77][78][79][80][81][82][83]. The enthalpy of the most economical ring opening via an initial cleavage of C C bond kcal/mol, is only a little preferred to the C N homolysis, 58.3/56.8 kcal/mol.…”

“…The only exception was 1,3-disiletane, which being diradical, CH 2 SiH 2 CH 2 SiH 2 , decomposed endothermically. Since decomposition of the diradical containing two silicon atoms required extra energy, raising the enthalpy of the overall reaction to 78.9 kcal/mol, 1,3-disiletane was predicted to be highly resisting INTRODUCTION Recently, 2 + 2 cycloreversion has been reviewed as a route to the doubly bonded hetero-π -systems [1]. The direction and even possibility of the four-membered rings to cyclorevert is strongly affected by the nature, number, and position of heteroatoms; in some cases making the mechanism of the process rather tentative.…”

Theoretical Study on the Ring-Opening of 1,3-Disilacyclobutane and H2 Elimination

“…Silicon is known to be reluctant to make p π −p π bonds. 1 The relative stability of SMS is attributed to the fact that it contains only Ring-Opening by 1,2-H shift. The decomposition of 1,3-DSCB initiated by a 1,2-H shift from Si to C accompanied by simultaneous ring-opening was first proposed by Auner et al 14 As illustrated in Scheme 2, an H shift from one of the two Si atoms to the adjacent C atom leads to the formation of an open-chain silylene, 1,3-disilabut-1-ylidene (II-a, Figure 4a).…”

“…3,14 This is in contrast to the wellknown results from the thermal decomposition of 1,1-dimethylsilacyclobutane, which was shown to be a clean unimolecular cycloreversion reaction to produce ethene and transient 1,1-dimethylsilene. 1,17,18 Barton et al found that both cycloreversion and ring-opening initiated by 1,2-H shift occurred in the pyrolysis of 1-silacyclobutane (1-SCB), the monosilacyclobutane analogue of 1,3-DSCB; however, the product from the latter is only 16% of the one from cycloreversion. 19 The decomposition in the photolysis of 1,3-DSCB, however, occurs mainly via cycloreversion, forming silenes.…”

Silaphenolates and Silaphenylthiolates: Two Unexplored Unsaturated Silicon Compound Classes Influenced by Aromaticity

“…In the context of unsaturated silicon compounds it is noteworthy that compounds with isolated Si=C double bonds, the so-called silenes [ 7 , 8 , 9 , 10 , 11 , 12 ], have a reduced tendency for dimerization when the Si=C bond is influenced by reverse Si=C bond polarity, i.e. , an Si δ− =C δ+ bond polarity rather than the natural Si δ+ =C δ− bond polarity [ 13 , 14 ].…”