Synthesis and structural characterization of Pd(II) and Pt(II) complexes with P-bonded 1′-(diphenylphosphino)ferrocenecarboxylic acid

Abstract

The title hybrid phosphine ligand (Hdpf) coordinates to Pt(II) and Pd(II) as a monodentate phosphine. In the absence of deprotonating agents, its carboxyl group remains uncoordinated to metal, but takes part in various types of hydrogen bonding. Using K 2MCl 4 as the metal ion source, trans-square planar complexes of the M(Hdpf- P) 2X 2 type (MPd, XCl, Br; MPt, XCl) were obtained. While Pd(Hdpf- P) 2Cl 2 is formed also from Pd(cycloocta-1,5-diene)Cl 2, the analogous Pt(II)–cod complex provides cis-square planar Pt(Hdpf- P) 2Cl 2. The trans-chlorides behave inconsistently on recrystallization from carboxylic acids. While acetic acid gives single crystals of the solvates M(Hdpf- P) 2Cl 2·2 AcOH, propionic or formic acid does not form solvates with Pt(Hdpf- P) 2Cl 2 at comparable conditions. Single crystal X-ray structure determination of the last four complexes revealed remarkable differences in the conformation of the ferrocenyl moiety and in inter- and intramolecular hydrogen bonding. The two isostructural solvates have molecular arrangement with solvent molecules hydrogen-bonded to the carboxyl groups of the ligand, thus saturating their hydrogen-bond capability. As can be expected, the structure of the unsolvated trans-Pt(Hdpf- P) 2Cl 2 is that of a one-dimensional polymer linked by intermolecular hydrogen bonds. Finally, the cis-complex is dimeric in the crystal, being joined by pairs of the peripheral carboxyls; there is a further bonding π– π interaction between the phenyl groups of the cis-phosphines.