Synthesis of strained ring compounds: Precursors to disilyne via molecular beam method
Description
Carbon-carbon double and triple bonds are very common in organic chemistry whereas the multiple bonds between silicon atoms are rare. Much of our knowledge about simple disilynes like dimethyldisilyne and diphenyldisilyne are based on theoretical calculations. The obstacles that prevent the synthesis and observation of simple disilynes are (i) the existence of a more stable isomer (for example in the case dimethyldisilyne, the dimethyldisilavinylidene isomer) (ii) the small energy barriers for isomerization, (iii) their intrinsically high reactivity. Therefore the generation of these simple disilynes is a great challenge and of great value for silicon chemistry. Reactive laser ablation coupled with molecular beam techniques is a powerful tool to study this type of highly reactive species. Potential precursors to the generation of disilynes are highly strained bis(silirane)s (Me4C2SiR)2 A series of strained three membered substituted bis(silirane)s (Me 4C2SiR)2 (where R = tert-butyl, Me, Ph) were synthesized. The tert-butyl substituted bis(silirane) has conformational rigidity in solution in contrast with its methyl and phenyl analogs which was observed by the appearance of four distinct methyl groups of the silirane ring in its 1H and 13C{ 1H} NMR spectra. This is consistent with a high rotational barrier of 30 kcal/mol along the Si-Si bond as determined by density functional theory calculations Preliminary laser ablation experiments on the tert-butylsubstituted bis(silirane) suggested that tBuSi≡Si tBu as well as a four membered cyclic disilene Me4C 2(SitBu)2 could be gas-phase intermediates An interesting silirane Me4C2Si(SiMe2Ph) 2 was synthesized, to investigate its decomposition pathway since it may form either the bis(dimethylphenylsilyl)silylene (Me2PhSi) 2Si: and tetramethylethylene or the cyclic silylene (Me2C) 2Si: and Me2PhSiSiMe2Ph. This silirane photochemically as well as thermally extrude the (Me2PhSi)2Si: quantitatively. The extruded silylene was intercepted with triethylsilane, trimethylmethoxysilane and bis(trimethylsilyl)acetylene The reaction of CH3(SiPcnBu8)Cl with KC8 or alkali metals to generate Wurtz coupling product CH 3(SiPcnBu8)2CH3, a cofacial phthalocyanine dimer with a direct Si-Si bond was studied. The failure of this reaction was studied by examining the electrochemistry and spectroelectrochemistry of CH3(SiPcnBu8)Cl. The failure of this compound to undergo reductive coupling is attributed to the stability of the anions produced by reduction