Synthetic and mechanistic studies of silylenium ions in solution

Abstraction of hydride from silyl hydrides by triphenylmethyl salts in methylene chloride apparently results in the formation of transient silylenium ions. Dimethylsilyl triphenylmethyl ether, dimethylsilyl t-butyl ether, benzyl dimethylsilyl ether, dimethylsilyl p-methoxybenzyl ether and dimethylsilyl diphenylmethyl ether, compounds with good carbocation leaving groups, afford cyclosiloxane oligomers in high yields under mild conditions suggesting the involvement of transient silylenium ions via abstraction of hydrides by triphenylmethyl salts. In the case of dimethylsilyl triphenylmethyl ether, triphenylmethyl cation can be regenerated in the reaction, so that triphenylmethyl salts can then be used as catalysts. From dimethylsilanone trapping experiments, it appears that these silylenium ions either decompose to free silanone or undergo an intermolecular silanone-transfer reaction. These results are the first to demonstrate the synthetic use of silylenium ions in solution;Olefins which contain both an ether group and a dimethylsilyl group on the same side of the double bond can cyclize into unsaturated five- and six-membered ring cyclic silyl ethers upon treatment with triphenylmethyl salts. Saturated compounds with an ether group and dimethylsilyl group can cyclize into saturated five- and six-membered ring cyclic silyl ethers. Mechanisms involving oxonium ion intermediates are proposed to account for the products;Attempts to generalize the same fragmentation process of silylenium ions to form silenes and disilenes failed. An attempt to use triphenylsilyl as the leaving group also failed to yield the desired cyclosiloxane oligomers using the same silylenium ion fragmentation scheme