The two-step synthesis of a new unsymmetrical ligand 2-{Ph2PC6H4C(H)=N} C6H4 {N(H) COCH2N( H) CO(2)Bz}, 2 center dot HH, via acid- catalyzed Schiff base condensation of 2-(H2N) C6H4 {N(H) COCH2N(H) CO(2)Bz}, 1, with 2-Ph2PC6H4( CHO) in refluxing EtOH is reported. The multidentate ligand 2 center dot HH, isolated in ca. 60% yield, exhibits an array of ligation modes, as exemplified by coordination studies with Ni-II, Pd-II, Pt-II, and Au-I mononuclear metal precursors. Hence, reaction of 2 center dot HH with AuCl(tht) ( 1: 1 molar ratio, tht = tetrahydrothiophene) affords AuCl(2 center dot HH), 3, in which the ligand behaves as a classic, neutral two-electron phosphorus donor. In contrast, reaction with MCl2(cod) (M = Pt, Pd; cod = cycloocta-1,5-diene) affords the corresponding dichloro complexes MCl2(2 center dot HH) (4a M = Pt; 4b M = Pd) in which kappa(2)-P/N-chelation through both P and imino N-donor atoms is observed. Likewise, treatment of Pd(CH3) Cl(cod) with 2 center dot HH gave Pd(CH3) Cl(2 center dot HH), 4c, in which the imino nitrogen is trans to the methyl ligand. Cycloocta-1,5-diene elimination from, and single methyl protonation of, Pt(CH3)(2)(cod) with 1 equiv of 2 center dot HH in toluene at ambient temperature affords the neutral complex Pt(CH3)(2 center dot H-), 5a, in which 2 center dot H- functions effectively in a kappa(3)-PNN' coordination mode. The dichloro compounds 4a or 4b undergo smooth N(H) deprotonation with (BuOK)-Bu-t to give 6a\6a' and 6b\ 6b' in which 2(2-) acts as a dianionic kappa(4)-PNN' N '' ligand. The corresponding square-planar, diamagnetic, nickel(II) complex 6c\6c' was prepared in excellent yield from NiCl2 center dot 6H(2)O, 2 center dot HH, and (BuOK)-Bu-t. Variable-temperature NMR experiments confirm 6a\ 6a' and 6b\ 6b' exist, in solution, as a pair of conformational ( anti and syn) isomers due to restricted rotation about the N - CO(2)Bz group. This feature is also borne out by single-crystal X-ray studies of anti-6a center dot CHCl3, syn-6a' center dot H2O, anti-6b center dot CHCl3, and anti-6c center dot CH2Cl2. To the best of our knowledge, we believe these constitute the first examples of crystallographically characterized conformers of a tetradentate ligand incorporating a P-donor center. All new compounds reported have been fully characterized by a combination of spectroscopic (NMR, FT-IR, ES-MS) and analytical methods. Furthermore, single-crystal X-ray studies have also been undertaken on compounds 2 center dot HH, 3, 4a, and 5a center dot Et2O.