Selectivity Control of the Ligand Exchange at Carbon in α‐Metallated Ylides as a Route to Ketenyl Anions**

Abstract

Abstractα‐Metallated ylides have recently been reported to undergo phosphine by CO exchange at the ylidic carbon atom to form isolable ketenyl anions. Systematic studies on the tosyl‐substituted yldiides, R3P=C(M)Ts (M=Li, Na, K), now reveal that carbonylation may lead to a competing metal salt (MTs) elimination. This side‐reaction can be controlled by the choice of phosphine, metal cation, solvent and co‐ligands, thus enabling the selective isolation of the ketenyl anion [Ts−CCO]M (2‐M). Complexation of 2‐Na by crown ether or cryptand allowed structure elucidation of the first free ketenyl anion [Ts−CCO]−, which showed an almost linear Ts−C−C linkage indicative for a pronounced ynolate character. However, DFT studies support a high charge at the ketenyl carbon atom, which is reflected in the selective carbon‐centered reactivity. Overall, the present study provides important information on the selectivity control of ketenyl anion formation which will be crucial for future applications.