Mechanistic Study of Stepwise Methylisocyanide Coupling and C–H Activation Mediated by a Low-Valent Main Group Molecule

An
experimental and DFT investigation of the mechanism of the coupling
of methylisocyanide and C–H activation mediated by the germylene
(germanediyl) Ge­(ArMe6)2 (ArMe6 = C6H3-2,6­(C6H2-2,4,6-Me3)2) showed that it proceeded
by initial MeNC adduct formation followed by an isomerization involving
the migratory insertion of the MeNC carbon into the Ge–C ligand
bond. Addition of excess MeNC led to sequential insertions of two
further MeNC molecules into the Ge–C bond. The insertion of
the third MeNC leads to methylisocyanide methyl group C–H activation
to afford an azagermacyclopentadienyl species. The X-ray crystal structures
of the 1:1 (ArMe6)2GeCNMe adduct,
the first and final insertion products (ArMe6)­GeC­(NMe)­ArMe6 and (ArMe6)­GeC­(NHMe)­C­(NMe)­C­(ArMe6)­NMe were obtained. The DFT calculations on the reaction pathways
represent the first detailed mechanistic study of isocyanide oligomerization
by a p-block element species.