Synthesis and structural characterization of rac-2-[(diphenylphosphino)methyl]ferrocenecarboxylic acid, its selected derivatives and some rhodium complexes

rac-2-[(Diphenylphosphino)methyl]ferrocenecarboxylic acid (1) was prepared in a good yield from rac-2-(N,N-dimethylaminomethyl)bromoferrocene (2) via rac-2-(hydroxymethyl)bromoferrocene (4) and rac-2-[(diphenylphosphino)methyl]bromoferrocene (5), and further converted to the respective phosphine oxide (6), phosphine sulfide (7) and methyl ester (8). The phosphines 1 and 8 were studied as ligands in rhodium complexes. The reaction of di-μ-chloro-bis[chloro-(η5-pentamethylcyclopentadienyl)rhodium(III)] with the stoichiometric amounts of 1 and 8 yielded the corresponding mononuclear complexes with P-monodentate ligands: [RhC2(η5-C5Me5)(L-κP)], 9 and 10, respectively. Attempted deprotonation of 9 with LiBu or KOt-Bu gave intractable mixtures, in which the parent complex 9 as the major component was accompanied by two new compounds, likely the diastereoizomeric phosphinocarboxylate complexes. A defined O,P-chelating phosphinocarboxylate complex, [SP-4-2]-carbonyl-[rac-2-{(diphenylphosphino)methyl}ferrocenecarboxylato-κ2O,P]-tricyclohexylphosphinerhodium(I) (12), was obtained from the displacement of acetylacetonate(1−) (acac) ligand in [Rh(acac)(CO)(PCy3)] (Cy = cyclohexyl) with acid 1. The structures of 1, 6 · CHCl3, and 7 · 1/2 CH2Cl2, 10, and hydrated complexes 9 and 12 were determined by single-crystal X-ray diffraction.