Methyl- and Acetylpalladium(II) Complexes Containing a P,N,O Tridentate Hydrazone Ligand

Abstract

The hydrazone ligand 2-(diphenylphosphanyl)benzaldehyde benzoylhydrazone (HPNO) forms the methyl PdII complex [Pd(HPN)(Me)Cl] (1) in high yield when treated with [(COD)Pd(Me)Cl] in dichloromethane or diethyl ether at room temperature. In complex 1, the ligand remains neutral and is P,N bidentate. The deprotonation of the ligand by Et3N affords [Pd(PNO)(Me)] (2), in which the anionic ligand is P,N,O tridentate. When 1 is treated with AgCF3SO3, the cationic complex [Pd(HPNO)(Me)]+[CF3SO3]− (3) is formed; here the neutral ligand coordinates in a tridentate P,N,O fashion. All three methyl complexes were subjected to 30 atm of CO pressure, resulting in the isolation of the corresponding acetyl complexes [Pd(HPN)(MeCO)Cl] (4), [Pd(PNO)(MeCO)] (5) and [Pd(HPNO)(MeCO)]+[CF3SO3]− (6). Complex 4 is completely stable in solution in the absence of CO, whereas 5 and 6 quickly decarbonylate to regenerate the starting methyl complexes 2 and 3. Complexes 5 and 6 can also be obtained in high yields by treatment of 4 with Et3N and AgCF3SO3, respectively. The X-ray crystal structures of the complexes 2, 5 and 6 were determined.