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.

    URL link for article: http://pubs.acs.org/doi/abs/10.1021/jacs.6b13275