The combination of 8-quinolyltrimethylstannane with GaCl3 led to a transmetalation reaction and formation of dichloro-8-quinolylgallium(III). The compound was obtained as a viscous resin that was insoluble in non-polar solvents, hexane or toluene. It was highly soluble in pyridine, and recrystallization gave the adduct with pyridine bound to gallium. In freshly distilled chloroform, a reaction took place and colorless crystals of the zwitterion, trichloroquinolinium-8-ylgallate(III) were formed. This product suggested the possibility of C-Cl activation in the presence of the intramolecular frustrated Lewis pair. Lewis acids have been widely used for halide abstraction to initiate reactions (for example, the Friedel-Crafts reaction), and recent work has shown that C-F activation could be achieved with frustrated Lewis pairs containing strong electrophiles with high affinity for fluoride. Therefore, it is reasonable to hypothesize that the title molecule abstracted chloride from chloroform to give a CHCl2+ carbocation intermediate, followed by proton transfer to the basic quinoline nitrogen to form the zwitterionic product. Deprotonation of CHCl2+ is a known mechanism for the formation of dichlorocarbene (:CCl2). A 13C NMR analysis of the chloroform supernatant indicated the presence of tetrachloroethylene (Cl2C=CCl2) that could form upon dimerization of dichlorocarbene. The results suggest exciting possibilities for C-Cl activation with dichloro-8-quinolylgallium(III).

Intramolecular frustrated Lewis pair dichloro-8-quinolylgallium(III) activates chloroform

251st National Meeting (2016)

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