Coordination Studies of a New Unsymmetrical κ4-PNN‘N‘ ‘-Tetradentate Ligand: Stepwise Formation and Structural Characterization

The two-step synthesis of a new unsymmetrical ligand 2-{Ph2PC6H4C(H)N}C6H4{N(H)COCH2N(H)CO2Bz}, 2·HH, via acid-catalyzed Schiff base condensation of 2-(H2N)C6H4{N(H)COCH2N(H)CO2Bz}, 1, with 2-Ph2PC6H4(CHO) in refluxing EtOH is reported. The multidentate ligand 2·HH, isolated in ca. 60% yield, exhibits an array of ligation modes, as exemplified by coordination studies with NiII, PdII, PtII, and AuI mononuclear metal precursors. Hence, reaction of 2·HH with AuCl(tht) (1:1 molar ratio, tht = tetrahydrothiophene) affords AuCl(2·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·HH) (4a M = Pt; 4b M = Pd) in which κ2-P/N-chelation through both P and imino N-donor atoms is observed. Likewise, treatment of Pd(CH3)Cl(cod) with 2·HH gave Pd(CH3)Cl(2·HH), 4c, in which the imino nitrogen is trans to the methyl ligand. Cycloocta-1,5-diene elimination fr...