B(C 6 F 5 ) 3 ‐Enabled Synthesis of a Cyclic cis ‐Arsaphosphene

The synthesis and characterization of an (arsino)phosphaketene, As(PCO){[N(Dipp)](CH 2 )} 2 (Dipp=2,6‐diisopropylphenyl) is reported along with its subsequent reactivity with B(C 6 F 5 ) 3 . When reacted in a stoichiometric ratio, B(C 6 F 5 ) 3 drove the insertion of the P=C bond of the phosphaketene into one of the As−N bonds of the arsino functionality, affording an acid‐stabilized, seven‐membered, cyclic arsaphosphene. In contrast, when catalytic amounts of B(C 6 F 5 ) 3 were employed, dimeric species, which formed through a formal [2+2] cycloaddition of the cyclic arsaphosphene, were generated. The cyclic arsaphosphene product represents the first example of such a compound in which the two substituents are arranged in a cis ‐configuration.