Trimerization of Phenylacetonitrile. InMe₃ as a Base for C−H Acidic Nitriles

The reaction of phenylacetonitrile with InMe₃ in boiling toluene in a molar ratio of 3:1 leads to a trimerization of the nitrile with evolution of methane. The presence of CsF accelerates the reaction. The colorless product was recrystallized from toluene/TMEDA to give 2-amino-1-[Me₂In(TMEDA)]-4-amino-3,5-diphenyl-6-benzylpyridine (6). A similar reaction of Ph₂CHCN with InMe₃ in boiling toluene gives not the product of a trimerization but a metalla-substituted ketenimine which crystallizes after addition of THF as the dimer [Ph₂CCNInMe₂(THF)]₂ (7). The reaction was monitored by ¹H NMR spectroscopy, exhibiting a equilibrium with a 0.5(7) to nitrile ratio of 82:18 mol %. CsF accelerates this reaction as well. Quite similarly, the reaction between GaMe₃ and Ph₂CHCN proceeds to give [Ph₂CCNGaMe₂]₂ (8), but the position of the equilibrium 0.5(8):Ph₂CHCN is more unfavorable (34:66 mol %). A complete transfer to 7 or 8 was observed when [Ph₂CCNLi(OEt₂)₂]₂ (9) was added to Me₂InCl or Me₂GaCl. 6, 7, 9, and Ph₂CHCN were characterized by NMR and vibrational spectroscopy as well as by X-ray structure analyses. According to these, 6 shows a delocalization of π-electrons over the six-membered ring and the amino/amido functions. The In atom possesses coordination number (CN) 5 with an In−N single bond of 2.180(3) Å and two weak donor−acceptor bonds of 2.439(3) Å (pyridine) and 2.533(3) Å (TMEDA). The ketenimine sequence in 7 shows CC distances of 1.35 Å and CN distances of 1.20 Å (mean values). The unit cell of the dimer 9 consists of two crystallographically unique molecules with almost planar four-membered Li₂N₂ rings.