Syntheses and Characterization of Palladium Complexes with a Hemilabile “PCO” Pincer Ligand

The synthesis of a new pincer ligand (^tBuPCO = 2-(CH₂P^tBu₂)-6-(CH₂OCH₃)C₆H₃) is reported. This ligand has been observed to coordinate in three different modes to palladium. The ^tBuPCO ligand coordinates in a monodentate fashion through the phosphine moiety in the dimeric [(^tBuPCO)Pd(Cl)(μ-Cl)]₂. Bidentate coordination is observed through the phosphine and the aryl ring in the binuclear [(^tBuPCO)Pd(μ-OH)]₂. The traditional tridentate coordination mode of a pincer is observed in the monomeric complex (^tBuPCO)PdCl, wherein the ether oxygen provides the third point of attachment. Each of these novel palladium(II) complexes was characterized by NMR spectroscopy, elemental analyses, and single-crystal X-ray crystallography. A variety of other palladium(II) complexes of ^tBuPCO have also been prepared and characterized, including the hydroxide complex (^tBuPCO)PdOH. The reactivity of the hydroxide complex with CO₂, CO, and H₂ is reported.