Of Ketenes and Carbenes

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Science  02 Jun 2000:
Vol. 288, Issue 5471, pp. 1549
DOI: 10.1126/science.288.5471.1549c

A number of important synthetic reactions take advantage of the formation of a ketene (which contains a C=C=O group) from a carbene (containing M=C) and a carbonyl (M-CO) that are coordinated to the same metal center. Adding a new ligand augments the electronic sphere of the metal and allows the carbene and carbonyl to combine with each other.

Grotjahn et al. now have observed this reaction running in reverse in a complex containing a single iridium atom. The key was finding a ligand that would create an open coordination site next to the ketene, in this case, the chelating diphosphine (tert-butyl)2PCH2P(tert-butyl)2. Removal of the chloride ligand through the formation of AgCl yielded the carbene-Ir-carbonyl complex. This reaction could be driven backwards to the ketene by addition of chloride. The synthesis of other analogs of this system should reveal insights into the steric and electronic factors that control this interconversion.—PDS

J. Am. Chem. Soc., in press

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