Isolable <i>C</i> ‐Phosphonio‐Boratavinyl Anion

ABSTRACT A persistent C ‐phosphonio boratavinyl anion 1 has been successfully synthesized. This boron‐containing vinyl‐lithium 1 , featuring a vinyl carbon with a negative charge (−1.59), considerably higher than that of carbon analogue 7 (−0.76), exhibits strongly nucleophilic and basic properties, as demonstrated by the results of rapid reactions with H 2 (10 bar, 15 min or 1 bar, 2 h at RT) and C 6 F 6 (1 equiv., 15 min at −80°C). The reactions of boratavinyl anion 1 with electrophiles offer a convenient route for the introduction of a borata‐alkene‐based bulky and σ,π‐double‐donating substituent, enabling to efficiently stabilize reactive intermediates such as halogenogermylenes. Furthermore, the reaction with CO 2 takes place at the borata‐alkene moiety, rather than at the P‐ylide function, resulting in the double insertion of CO 2 into the B─C bond to afford a unique cyclic P‐ylide 13 .