Trimerization of Phenylacetonitrile. InMe<sub>3</sub> as a Base for C−H Acidic Nitriles

2003-09-29T00:00:00Z (GMT) by Effat Iravani Bernhard Neumüller
The reaction of phenylacetonitrile with InMe<sub>3</sub> 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-[Me<sub>2</sub>In(TMEDA)]-4-amino-3,5-diphenyl-6-benzylpyridine (<b>6</b>). A similar reaction of Ph<sub>2</sub>CHCN with InMe<sub>3</sub> in boiling toluene gives not the product of a trimerization but a metalla-substituted ketenimine which crystallizes after addition of THF as the dimer [Ph<sub>2</sub>CCNInMe<sub>2</sub>(THF)]<sub>2</sub> (<b>7</b>). The reaction was monitored by <sup>1</sup>H NMR spectroscopy, exhibiting a equilibrium with a 0.5(<b>7</b>) to nitrile ratio of 82:18 mol %. CsF accelerates this reaction as well. Quite similarly, the reaction between GaMe<sub>3</sub> and Ph<sub>2</sub>CHCN proceeds to give [Ph<sub>2</sub>CCNGaMe<sub>2</sub>]<sub>2</sub> (<b>8</b>), but the position of the equilibrium 0.5(<b>8</b>):Ph<sub>2</sub>CHCN is more unfavorable (34:66 mol %). A complete transfer to <b>7</b> or <b>8</b> was observed when [Ph<sub>2</sub>CCNLi(OEt<sub>2</sub>)<sub>2</sub>]<sub>2</sub> (<b>9</b>) was added to Me<sub>2</sub>InCl or Me<sub>2</sub>GaCl. <b>6</b>, <b>7</b>, <b>9</b>, and Ph<sub>2</sub>CHCN were characterized by NMR and vibrational spectroscopy as well as by X-ray structure analyses. According to these, <b>6</b> 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 <b>7</b> shows CC distances of 1.35 Å and CN distances of 1.20 Å (mean values). The unit cell of the dimer <b>9</b> consists of two crystallographically unique molecules with almost planar four-membered Li<sub>2</sub>N<sub>2</sub> rings.