The stability of this unusual unsaturated molecule is undoubtedly due to its negative charge, which confers stability with respect to dimerization or oligomerization by nature of electrostatic repulsion. This draws parallels with other fundamental unsaturated main-group molecules such as [PCO] -, where the reactive P-C multiple bond is stabilized with respect to dimerization by the same electrostatic repulsion, instead of requiring kinetic stabilization from bulky substituents such as those seen in neutral phosphaalkynes. Compound 1 is stable under inert conditions and can be obtained on a multigram scale in excellent yield. This prompted us to probe various aspects of its reactivity. Our first target was the parent cyanoketene. Diffusion of HCl gas into a benzene solution of 1 at 10 °C resulted in formation of a cloudy yellow suspension, and after work-up the product was obtained as 2 (Scheme 2). This species was confirmed by single crystal X-ray diffraction to be a dimer (Figure ) comprising a four-membered core presumed to form from a head-to-tail [2+2] cycloaddition reaction of the parent cyanoketene and another equivalent of 1. In the corresponding reaction of 1 with a more sterically demanding electrophile Ph3SiCl, the product (3) also contained a monoanionic four-membered core (Figure ). Interestingly, a similar dimeric product was obtained in the reaction of 1 with CO2 at 10 °C. The resulting pale yellow cloudy suspension afforded the product 4 in a 76% isolated yield (Figure ). This species contains two [K(18-crown-6)] + cations and a dianionic component, where the negative charges are delocalized in OCCCO moiety across the fourmembered core (as in 2 and 3), and the carboxylate fragment.