The steric tuning of a tridentate acridane-derived NNN pincer ligand allows for the isolation of a strictly Tshaped phosphine that exhibits ambiphilic reactivity. Welldefined phosphorus-centered reactivity towards nucleophiles and electrophiles is reported, contrasting with prior reports on this class of compounds. Reactions towards oxidants are also described. The latter result in the two-electron oxidation of the phosphorus atom from + III to + V and are accom-panied by a strong geometric distortion of the NNN pincer ligand. By contrast, cooperative activation of EÀ H (HCl, HBcat, HOMe) bonds proceeds with retention of the phosphorus redox state. When using H 2 O as a substrate, the reaction results in the full disassembly of H 2 O to its constituent atoms, highlighting the potential of this platform for small molecule activation reactions.