Potentially tridentate hydrazonic ligands in the synthesis of methyl and acetyl palladium(II) complexes

Potentially tridentate hydrazonic ligands of the type HNNO have been used i n the synthesis of some methyl palladium(II) complexes. Depending on the ap plied experimental conditions two different kinds of complexes are obtained . Thus, the reactions between HL1-HL5 and (COD)PdMeCl in diethyl ether led to the formation of bidentate methyl complexes of the type Pd(HNN)MeCl (1-5 ), where the Ligands maintain a neutral character. However, in the presence of a base such as Et3N or NaOMe, the ligands are deprotonated with the con sequent formation of tridentate methyl complexes of the type Pd(NNO)Me (7-1 0). In solution, complexes 1-5 tend to lose the hydrazonic proton with elim ination of methane and formation of a tridentate chloride complex Pd(NNO)Cl (6); this tendency can be correlated with the acidity of the free Ligands, which has been determined. On bubbling carbon monoxide through solutions o f 1-5, the corresponding acetyl complexes Pd(HNN)[C(O)Me]Cl (11-15) are for med, in which both the cis and trans isomers are present. Their molar ratio is rationalised from the results of a molecular modelling study on the bas is of electronic considerations. A remarkably different reactivity has been found in the carbonylation of the tridentate complexes 7-10: they decompos e rapidly and quantitatively to palladium black and an organic product corr esponding to the ligand with an acetyl group bonded to the hydrazonic nitro gen. The X-ray structures of a methyl complex (3) and its corresponding ace tyl (13) derivative have been determined.