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

作者：Son Jung Ho; Tamang Sem Raj; Fostvedt Jade I; Hoefelmeyer James D^*

来源：Organometallics, 2017, 36(2): 474-479.

DOI：10.1021/acs.organomet.6b00867

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-mu-(quinolin-8-y1)-mu-chloro-dichlorodigallium(III) tetrachloro-gallate 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.

• 出版日期2017-1-23