Synthesis and characterization of neutral and anionic carbonyl derivatives of palladium(ii)

Abstract

The action of CO on the solvento-complexes cis-[PdR₂(thf)₂] [R = C₆F₅ (1), C₆Cl₅ (2)] at low temperature gives cis-[PdR₂(CO)₂] [R = C₆F₅ (3), C₆Cl₅ (4)] in good yield by simple replacement of the highly labile thf molecules. These are rare cases of Pd^II dicarbonyl compounds, whose characterization relies on spectroscopic and analytic data. The crystal structure of the square-planar platinum homologue cis-[Pt(C₆Cl₅)₂(CO)₂] is also presented. CO can split the double bridging-system in the dinuclear species [{PdR₂}₂(μ-X)₂]²⁻ giving the homologous series of anionic monocarbonyl Pd^II derivatives with formula [cis-PdR₂X(CO)]⁻ (5–10: R = C₆F₅, C₆Cl₅; X = Cl, Br, I), which were isolated (except for the R = C₆F₅ and X = I) and suitably characterized. Characterization includes the crystal and molecular structure of [PPh₃Me][cis-Pd(C₆F₅)₂Br(CO)] (6′). The anionic species [NBu₄][cis-Pd(C₆F₅)₂Cl(CO)] (5) reacts with neutral cis-[Pd(C₆F₅)₂(CO)₂] (3) under CO extrusion, affording the dinuclear derivative [NBu₄][{Pd(C₆F₅)₂(CO)}₂(μ-Cl)] (11), which contains a single unsupported halide bridge (X-ray diffraction). Complex 11 can be considered as modelling a possible intermediate step in intermolecular CO substitution reactions that are easily undergone by Pd^II halo carbonyl species.