Intramolecular Lewis acid–base pairs based on 4-ethynyl-2,6-lutidine

Abstract

The reaction of 4-ethynyl-2,6-lutidine, (2,6-Me₂)(4-HCC)C₅H₂N (2), with B(C₆F₅)₃ afforded the zwitterion [(2,6-Me₂)(4-(C₆F₅)₃BCC)C₅H₂NH] (3) via a deprotonation pathway. By treatment of 2 with the group 13 trialkyls AlMe₃, AlEt₃, GaMe₃, GaEt₃ and InMe₃, metallation of the ethynyl group afforded compounds 4–8 under extrusion of the corresponding alkane. The resulting products were characterised by elemental analyses and NMR spectroscopy. Compounds 4 and 8 were crystallized from THF and were yielded as monomers with coordinated THF molecules. The gallium compound 7 could be crystallised from benzene and was afforded as coordination polymer. The structures of these three compounds (4·THF, 7 and 8·2THF) were determined by single-crystal X-ray diffraction experiments. The aluminium compounds 4 and 5 show redistribution reaction of their substituents.