Reactions of Isocyanides with Metal Carbyne Complexes: Isolation and Characterization of Metallacyclopropenimine Intermediates

η2-Iminoketenyl species have often been postulated
as the intermediates in nucleophile-induced carbyne–isocyanide
C–C coupling processes. However, such species are elusive.
Here we report direct formation of η2-imino­ketenyl
complexes from reactions of metalla­pentalyne with isocyanides.
Our studies show that steric effects of N-substituents of the isocyanides
play an important role in the stability of the three-membered metalla­cycles
of the η2-imino­ketenyl complexes. Sterically
bulky isocyanides, such as tert-butyl or 1-adamantyl
isocyanides, inhibit bending at the isocyanide nitrogen atoms, a requirement
for formation of η2-imino­ketenyl structures.
Reactions of metalla­pentalyne with excess isocyanide allow the
metal-bridged metalla­indene derivativesto be isolated as a result
of the isocyanide insertion into the M–Cα σ
bond of metalla­pentalyne.