text: is the pph2 anion in kpph2 a hard, soft or borderline base? please give your basis. i need to know this badly. i want to introduce the pph2 group to my system, a zr oxide cluster with dangling alkyl bromide groups. i don't know whether the pph2 anion from kpph2 attacks the zr cluster or replaces the bromides. i'm trying to use the hsab concept as a guide. i think it's safe to say that pph2 is soft, considering it has a phosphorus central atom with 2 benzene rings. the defining characteristic is that the molecule has a diffuse electron cloud, caused by the delocalized pi system in the benzene rings as well as the size of the phosphorus electron cloud.  as to your reaction, i'm not sure. is this a ligand substitution?