Dehydrodechlorination of Methylene Chloride, Chloroform, and Chlorodiphenylmethane in the Presence of Ga/N Lewis Pairs

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• 作者：Jung-Ho Son ; Sem Raj Tamang ; Jade I. Fostvedt ; James D. Hoefelmeyer
• 刊名：Organometallics
• 出版年：2017
• 出版时间：January 23, 2017
• 年：2017
• 卷：36
• 期：2
• 页码：474-479
• 全文大小：392K
• ISSN：1520-6041

文摘

Transmetalation occurs upon addition of GaCl₃ to (quinolin-8-yl)trimethylstannane. The compound dissolves immediately in pyridine, and recrystallization gives dichloropyridinyl(quinolin-8-yl)gallium(III). In chloroform, the compound bis-μ-(quinolin-8-yl)-μ-chloro-dichlorodigallium(III) tetrachlorogallate could be isolated in small quantities; however, the major product was trichloro(quinolinium-8-yl)gallate(III) zwitterion. The zwitterion also formed upon addition of methylene chloride or chlorodiphenylmethane. We hypothesize that the highly electrophilic digallyl cation abstracts chloride to form a carbocation and that proton transfer from the carbocation to the quinoline nitrogen affords transient carbenes. In particular, diphenyl carbene forms from dehydrodechlorination of chlorodiphenylmethane in toluene/cyclohexene to give a well-defined mixture of products due to cyclopropanation and C–H insertion reactions. Dichloropyridinyl(quinolin-8-yl)gallium(III) undergoes reaction with chloroform only at elevated temperature to yield quinolinium tetrachlorogallate salt as the product. This salt also forms in the reaction of chloroform with GaCl₃ and quinoline at elevated temperature. The zwitterion could be converted to quinolinium tetrachlorogallate upon heating, which supports the idea that it was formed initially as an intermediate. Thus, the Ga/N Lewis pairs appear capable of dehydrodechlorination of chloroalkanes.