The Organometallic Chemistry of Ph3P=C=C=O. A Route to Metal-Substituted Ketenes

Ketenylidenetriphenylphosphorane, Ph3P=C=C=O (1), presents, at a first glance, the characteristics of both ylides and ketenes, but its behavior is that typical of ylides, undergoing electrophilic attacks on the ylidic carbon that transform 1 into a ‘true’ ketene having PPh3 as one substituent. Here we review the synthesis, the chemical/ physical properties as well as the reactivity of these compounds, with a particular emphasis on the interaction with transition metal complexes. With this compound it has always been observed that the ylidic carbon of 1 binds to coordinatively unsaturated metals, which act as electrophiles, forming η1-ketenyl derivatives that can also be viewed as stabilized metal-substituted ketenes. Perspectives for the synthesis of other metal-substituted ketenes and developments on their study are also presented.