Reactivity of Rare Earth Metal Alkyl Complexes with Nitriles or Isonitrile: Versatile Ways toward Multiply...

The reactivity of the rare earth metal alkyl complexes LRE(CH₂SiMe₃)(THF)₂ (1) [RE = Y (1), Yb (1), Lu (1); L = 2,5-[(2-pyrrolyl)CPh₂]₂(N-methylpyrrole)] with various nitriles and isonitriles has been fully developed. Treatment of the yttrium monoalkyl complex (1) with 2 equiv of aromatic nitriles afforded the symmetric trisubstituted β-diketiminato yttrium complexes (2, 2, and 2) through successive cyano group insertion into the RE-C bond and 1,3-H shift or the unsymmetric trisubstituted β-diketiminato yttrium complex (3) unexpectedly via a 1,3-SiMe₃ shift when 4-(trifluoromethyl)benzonitrile was used in this reaction under the same conditions. By treating 1 with 2 equiv of tolyl acetonitrile, an activation of the sp³ C-H bond occurred to form the corresponding β-aryl keteniminato complexes 4 and 4. Remarkably, a heteroleptic cleavage of the CO-CN bond took place in the reaction of 1 with benzoyl nitrile, affording the unsymmetric trinuclear yttrium complex 5 bridged by three cyanide groups. Dinuclear ytterbium and lutetium complexes 6 and 6 containing a functionalized isoindole fragment were synthesized from the reactions of 1 with phthalonitrile by tandem insertion and cyclization. Further studies indicated that the temperature and stoichiometric ratio have a great influence on the reactivity patterns between the reactions of 1 with benzylisonitrile: two tetrasubstituted β-diketiminato complexes 8 and 9 were obtained at -30 °C, and tetrasubstituted imidazolyl yttrium and lutetium complexes 7 were isolated at elevated temperature, respectively. In addition, the tetrasubstituted β-diketiminato complexes 8 and 9 could be irreversibly converted to the cyclization products 7 by elevating the reaction temperature not only on the NMR scale but also on the preparative scale. Notably, when the phenyl isonitrile instead of benzyl isonitrile was reacted with 1, a 2,3-functionalized indolyl ytterbium complex 10 was isolated.