Stable Ketenyl Anions via Ligand Exchange at an Anionic Carbon as Powerful Synthons.

Under an atmosphere of carbon monoxide (CO), a (phosphino)diazomethyl anion salt [[P]-CN2 ][K(18-C-6)(THF)] (1) ([P]=[(CH2 )(NDipp)]2 P; 18-C-6=18-crown-6; Dipp=2,6-diisopropylphenyl) undergoes a facile N2 /CO exchange reaction giving the (phosphino)ketenyl anion salt [[P]-CCO][K(18-C-6)] (2). Oxidation of 2 with elemental Se affords the (selenophosphoryl)ketenyl anion salt [P](Se)-CCO][K(18-C-6)] (3). These ketenyl anions feature a strongly bent geometry at the P-bound carbon and this carbon atom is highly nucleophilic. The electronic structure of the ketenyl anion [[P]-CCO]- of 2 is examined by theoretical studies. Reactivity investigations demonstrate 2 as a versatile synthon for derivatives of ketene, enolate, acrylate and acrylimidate moieties.