We hypothesized that the logical exploration of late transition metal-PN chemistry could be facilitated via the development of rigid, multidentate PN platforms. Specifically, ligands designed to enforce quasilinear P-N-M linkages could maximize π-donation to a bound metal ion and enable the synthesis of stable, high valent complexes with unusual electronic properties or reactivity profiles. Herein, we report a mild, high yielding, and general synthetic procedure for the synthesis of phosphinimines (R3PNH) from the corresponding phosphines. This protocol was instrumental in the synthesis of a chelating, tris-PN framework featuring a rigid triarylbenzene backbone that stabilizes both mono-and multinuclear transition metal complexes. A trinuclear Co II 3 compound was found to react cleanly with O2 or C2Cl6 to afford an exceptionally-stable, high spin (S = 2) Co III complex. Experimental and computational studies corroborate strong metal-ligand multiple bonding to the terminally-bound PN ligands which serve to stabilize this unusual spin state for Co III . Our results highlight the importance of ligand design in harnessing the π-basicity of PNs for the synthesis of complexes with unusual geometric and electronic structures, and provide the synthetic groundwork for the general investigation of PNs with late transition metals.