(Phosphino)phosphaketenes (>P-P=C=O) behave as (phosphino)phosphinidene-carbonyl adducts (>P-P <-:C=O). CO scrambling was observed using C-13 labeled CO, and exchange reactions with phosphines afford the corresponding (phosphino)phosphinidene phosphine adducts (>P-P <-:PR3). The latter react with isonitriles and singlet carbenes giving (phosphino)phosphinidene isonitrile ( >P-P <-:CNR)and -carbene adducts (>P-P <-:C<). Based on experimental results and DFT calculations, it is shown that these "ligand" exchange reactions occur via an associative mechanism as classically observed with transition metal complexes.