Mono- and dinuclear palladium(II) cyclometallates with 4-R-N'-(mesitylidene)benzohydrazides and mono- and diphosphines

•Cyclopalladates of 4-R-N'-(mesitylidene)benzohydrazides (H2Ln) were synthesized.•Ancillary ligands used were Cl−, PPh3 and diphosphines for these palladacycles.•CHN analysis, X-ray crystallography and spectroscopy were used for characterization.•The complexes were validated as [Pd(HLn)Cl], [Pd(Ln)(PPh3)] and [Pd2(μ-diphos)(Ln)2].•(HLn)−/(Ln)2− act as methylene-C, azomethine-N and amide-/amidate-O donor ligands.

Reactions of PdCl2, LiCl, 4-R-N'-(mesitylidene)benzohydrazides (H2Ln; n = 1 and 2 for R = H and OMe, respectively) and NaOAc∙3H2O in 1:2:1:1 mol ratio in methanol produce [Pd(HLn)Cl] (1 (n = 1) and 2 (n = 2)) in ∼77% yields. Reactions of [Pd(HLn)Cl] (1 and 2) with PPh3 in 1:2 mol ratio in acetone provide [Pd(Ln)(PPh3)] (3 (n = 1) and 4 (n = 2)) in ∼76% yields. Whereas, treatment of 2 mol equivalents of [Pd(HLn)Cl] (1 and 2) with 1 mol equivalent of 1,4-bis(diphenylphosphino)butane (dppb) in acetone affords the dinuclear [Pd2(μ-dppb)(Ln)2] (5 (n = 1) and 6 (n = 2)) in ∼74% yields. Analogous reaction between [Pd(HL2)Cl] (2) and 1,1'-bis(diphenylphosphino)ferrocene (dppf) provides [Pd2(μ-dppf)(L2)2] (7) in 67% yield. Elemental (CHN) analysis, X-ray crystallographic and spectroscopic (IR, UV-Vis and NMR) measurements have been used to characterize all the complexes. In these complexes, the metal centers are in square-planar CNOCl or CNOP coordination geometry formed by the 6,5-membered fused chelate rings forming methylene-C, azomethine-N and amide- or amidate-O donor (HLn)− or (Ln)2− and the ancillary ligand chloride or phosphine. The spectroscopic properties of the complexes are consistent with the corresponding molecular structures established by X-ray crystallography.

Graphical abstractSyntheses, X-ray structures and spectroscopic characteristics of mono- and dinuclear palladacycles [Pd(HLn)Cl], [Pd(Ln)(PPh3)] and [Pd2(μ-dppb/dppf)(Ln)2] (H2Ln = 4-R-N'-(mesitylidene)benzohydrazides, dppb = 1,4-bis(diphenylphosphino)butane and dppf = 1,1'-bis(diphenylphosphino)ferrocene) are described. In these complexes, the ligands ((HLn)− and (Ln)2−) behave as methylene-C, azomethine-N and amide-/amidate-O donors.Figure optionsDownload full-size imageDownload as PowerPoint slide