The coordination behaviour of ferrocene-based pyridylphosphineligands towards ZnII, CdII and HgII

Abstract

The reaction of Group 12 metal dihalides MX₂ with the P,N-ligands [Fe(C₅H₄-PPh₂)(C₅H₄-2-py)] (1) (2-py = pyrid-2-yl), [Fe(C₅H₄-PPh₂)(C₅H₄-CH₂-2-py)] (2) and [Fe(C₅H₄-PPh₂)(C₅H₄-3-py)] (3) (3-py = pyrid-3-yl) was investigated. For a 1 : 1 molar ratio of MX₂ and the respective ligand, three structure types were found in the solid state, viz. chelate, cyclic dimer and chain-like coordination polymer. The M^II coordination environment is distorted pseudo-tetrahedral in each case. The P–M–N angle is much larger in the chelates (≥119°) than in the ligand-bridged structures (≤109°). 1 prefers the formation of chelates [MX₂(1-κ²N,P)]. 3 forms coordination polymers [MX₂(μ-3)]_n. With the more flexible 2 all three structure types can occur. Dynamic coordination equilibria were observed in solution for the molecular complexes obtained with 1 and 2. NMR data indicate that the N- and P-donor sites interact most strongly with Zn^II and Hg^II, respectively. While the formation of bis(phosphine)mercury complexes (soft–soft) was easily achieved, no bis(pyridine)zinc complex (borderline–borderline) could be obtained, which is surprising in view of the HSAB principle.