A Highly-Reduced Cobalt Terminal Carbyne: Divergent Metal- and α‑Carbon-Centered Reactivity

Reported here is
the isolation of a dianionic cobalt terminal carbyne
derived from chemical reduction of an encumbering isocyanide ligand.
Crystallographic, spectroscopic and computational data reveal that
this carbyne possesses a low-valent cobalt center with an extensively
filled d-orbital manifold. This electronic character renders the cobalt
center the primary site of nucleophilicity upon reaction with protic
substrates and silyl electrophiles. However, reactions with internal
alkynes result in [2+2] cycloaddition with the carbyne carbon to form
a new C–C bond.