Synthesis and structural characterisation of palladium and group-12 metal complexes with a hybrid phosphanylphosphonate ferrocene ligand

Diethyl [1'-(diphenylphosphanyl)ferrocenyl]phosphonate (1) was synthesised by stepwise metallation/functionalisation of 1,1'-dibromoferrocene and studied as a ligand for palladium(n) and group-12 metals. Treatment of [PdCl2(cod)] (cod = eta(2): eta(2)-cycloocta-1,5-diene) with 1 in 1:1 or 1:2 molar ratios gave, respectively, the dinuclear, chloride-bridged complex [{Pd(mu-Cl)Cl(1-kP(2))}(2)] (2) and the mononuclear complex trans-[PdCl2(1-kP(2))(2)] (3), where 1 coordinates exclusively through the phosphane function. The reactions between 1 and group-12 metal bromides MBr2 in a 1:1 molar ratio gave the adducts [MBr2(1)] [M = Zn (4), Cd (5), and Hg (6)], whose crystal structures change considerably with the metal ion. Thus, whereas 4 is a molecular complex with 1 coordinating as an O-1, P-2-chelate, its cadmium(II) analogue is a polymer built up from symmetric {CdBr(mu-Br)}(2) units interconnected by pairs of O-1,P-2-bridging phosphanylphosphonate ligands, Finally, the mercury(II) complex 6 is a halide-bridged dimer, [{Hg(mu-Br)Br(1-kP(2))}(2)]. However, this compound is structurally fluxional in solution (NMR spectra) and, in the crystal, it attains a structure similar to 5 owing to weak interactions between mercury and phosphonate-O-1 atoms from adjacent molecules. An isomer to 6, [{HgBr2(1-k(2)O(1),P-2)}(2)] (7), was isolated from attempted alkylation of 6 and structurally characterised as a dimer, where ligands 1 bridge two {HgBr2} units. All compounds were studied by spectroscopic methods (IR, NMR, mass) and the solid-state structures of 1, 2(2)(.)\(H2O)-H-1, 3(.)4 CHCl3, 4, 5, 6(.)5 C6H6, and 7 have been determined by single-crystal X-ray diffraction. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).