Synthesis and structural characterization of 1′-(diphenylphosphino)ferrocene-1-carboxamide, its corresponding hydrazide, some heterocycles derived from the hydrazide and palladium(II) complexes with these functional phosphinoferrocene ligands

Two polar phosphinoferrocene ligands, 1′-(diphenylphosphino)ferrocene-1-carboxamide (1) and 1′-(diphenylphosphino)ferrocene-1-carbohydrazide (2), were synthesized in good yields from 1′-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) via the reactive benzotriazole derivative, 1-[1′-(diphenylphosphino)ferrocene-1-carbonyl]-1H-1,2,3-benzotriazole (3). Alternatively, the hydrazide was prepared by the conventional reaction of methyl 1′-(diphenylphosphino)ferrocene-1-carboxylate with hydrazine hydrate, and was further converted via standard condensation reactions to three phosphinoferrocene heterocycles, viz 2-[1′-(diphenylphosphino)ferrocen-1-yl]-1,3,4-oxadiazole (4), 1-[1′-(diphenylphosphino)ferrocen-1-carbonyl]-3,5-dimethyl-1,2-pyrazole (5), and 1-[1′-(diphenylphosphino)ferrocene-1-carboxamido]-3,5-dimethylpyrrole (6). Compounds 1 and 2 react with [PdCl2(cod)] (cod = η2:η2-cycloocta-1,5-diene) to afford the respective bis-phosphine complexes trans-[PdCl2(L-κP)2] (7, L = 1; 8, L = 2). The dimeric precursor [(LNC)PdCl]2 (LNC = 2-[(dimethylamino-κN)methyl]phenyl-κC1) is cleaved with 1 to give the neutral phosphine complex [(LNC)PdCl(1-κP)] (9), which is readily transformed into a ionic bis-chelate complex [(LNC)PdCl(1-κ2O,P)][SbF6] (10) upon removal of the chloride ligand with Ag[SbF6]. Pyrazole 5 behaves similarly affording the related complexes [(LNC)PdCl(5-κP)] (12) and [(LNC)PdCl(5-κ2O,P)][SbF6] (13), in which the ferrocene ligand coordinates as a simple phosphine and an O,P-chelate respectively, while oxadiazole 4 affords the phosphine complex [(LNC)PdCl(4-κP)] (11) and a P,N-chelate [(LNC)PdCl(4-κ2N3,P)][SbF6] (14) under similar conditions. All compounds were characterized by elemental analysis and spectroscopic methods (multinuclear NMR, IR and MS). The solid-state structures of 1⋅½AcOEt, 2, 7⋅3CH3CN, 8⋅2CHCl3, 9⋅½CH2Cl2⋅0.375C6H14, 10, and 14 were determined by single-crystal X-ray crystallography.