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( II ) and group‐12 metals. Treatment of [PdCl 2 (cod)] (cod = η 2 :η 2 ‐cycloocta‐1,5‐diene) with 1 in 1:1 or 1:2 molar ratios gave, respectively, the dinuclear, chloride‐bridged complex [{Pd(μ‐Cl)Cl( 1 ‐κ P 2 )} 2 ] ( 2 ) and the mononuclear complex trans ‐[PdCl 2 ( 1 ‐κ P 2 ) 2 ] ( 3 ), where 1 coordinates exclusively through the phosphane function. The reactions between 1 and group‐12 metal bromides MBr 2 in a 1:1 molar ratio gave the adducts [MBr 2 ( 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(μ‐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(μ‐Br)Br( 1 ‐κ P 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 , [{HgBr 2 ( 1 ‐κ 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 {HgBr 2 } units. All compounds were studied by spectroscopic methods (IR, NMR, mass) and the solid‐state structures of 1 , 2· ${1 \over 2}$  H 2 O, 3· 4 CHCl 3 , 4 , 5 , 6· 5 C 6 H 6 , and 7 have been determined by single‐crystal X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)