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

The synthesis of a new pincer ligand (tBuPCO = 2-(CH2PtBu2)-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.