The unique features of anionic phosphinimides (PN)also known as imidophosphoranes -warrant further consideration in the stabilization of reactive inorganic fragments. The two canonical resonance structures of PNs (Fig 1A) highlight their ability to act as 1, 3, or 5 electron donors, attendant with the diversity of observed [PN-M] metal binding modes (Fig ). In the case of a terminally bound PN where the ∠(P-N-M) angle approaches 180 o , the PN moiety can serve as a 5 electron donor engaging in π-bonding with the metal center in two orthogonal planes, akin to imido ligands. The effectiveness of PNs as electron releasing substituents or donors has been exploited in the synthesis of phosphazene superbases and stable complexes of strongly oxidizing ions such as Ce(IV) and Tb(IV), respectively. As ligands, PNs also enable the generation of reactive, low-coordinate metal fragments via the incorporation of sterically-encumbering substituents on the phosphorus atom. This feature has been successfully used to generate a class of Ti-promoted olefin polymerization catalysts and Ni-or Co-promoted hydrogenation catalysts. High-valent states of late transition metal complexes are implicated as reactive intermediates in numerous synthetic and biological processes; isolation and characterization of such species is of great interest. In this context, the coordination of PNs to late transition metals as multielectron donors may be expected to stabilize high valent states of these metal ions. Excluding a small number of Ru and Os-PN complexes, very few mononuclear late transition metal-PN complexes have been reported (Fig 1B), often requiring the presence of sterically-demanding co-ligands to prevent oligomerization. This situation can be partially explained by significant dπ-pπ repulsive effects which are expected to impede the ability of PN ligands to serve as 3-or 5-electron donors. This general tendency of late transition metal-PN complexes to form oligomers -even with the usage of sterically-encumbering PN ligands such as t-Bu3PN --challenges synthetic efforts in this area. Figure . A) Canonical resonance structures of a phosphinimide (PN) functional group. B) Selection of metal-PN complexes, showing the diversity of metal binding modes and the propensity to make oligomeric structures with late first row transition metals.