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

α-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 tosyl-substituted metallated ylides (R3P=C(M)Ts) now reveal that carbonylation leads to either phosphine or metal salt (MTs) elimination. The selectivity of this reaction can be controlled by the nature of the phosphine and metal cation, the solvent and additional co-ligands, enabling full control of the selectivity and isolation of the ketenyl anion [Ts-CCO]M (2-M, M = Na, K) in high yields. Complexation of 2-Na by crown ether or cryptand allowed the structure elucidation of the first “naked” ketenyl anion [Ts-C=C=O]-, which showed only a slightly bent Ts-C-C linkage indicating pronounced ynolate character. However, DFT studies confirmed the high charge concentration at the ketenyl carbon, which is reflected in the selective carbon-centered reactivity of 2-M. In contrast to previously reported ketenyl anions, ketenes obtained from the tosyl-substituted anion 2-M reacted directly with the ketenyl anion to give convenient access to a range of cyclobutadiones. Overall, the present studies provide important information on the selectivity control of ketenyl anion formation which will be crucial for broader applications in the future.