Synthesis and coordination chemistry of a new N4-Polydentate class of pyridyl-functionalized scorpionate ligands: Complexes of Fe II, ZnII, NiII, VIV, PdII and use for heterobimetallic systems

Article abstract of DOI:10.1021/ic100966u

The new potentially N₄-multidentate pyridyl-functionalized scorpionates 4-((tris-2,2,2-(pyrazol-1-yl)ethoxy)methyl)pyridine (TpmPy, (1)) and 4-((tris-2,2,2-(3-phenylpyrazol-1-yl)ethoxy)methyl)pyridine (TpmPy ^Ph, (2)) have been synthesized and their coordination behavior toward Fe^II, Ni^II, Zn^II, Cu^II, Pd ^II, and V^III centers has been studied. Reaction of (1) with Fe(BF₄)₂ 6H₂O yields [Fe(TpmPy) ₂](BF₄)₂ (3), that, in the solid state, shows the sandwich structure with trihapto ligand coordination via the pyrazolyl arms, and is completely low spin (LS) until 400 K. Reactions of 2 equiv of (1) or (2) with Zn^II or Ni^II chlorides give the corresponding metal complexes with general formula [MCl₂(TpmPy)₂] (M = Zn, Ni; TpmPy* = TpmPy, TpmPy^Ph) (4-7) where the ligand is able to coordinate through either the pyrazolyl rings (in case of [Ni(TpmPy) ₂]Cl₂ (5)) or the pyridyl-side (for [ZnCl ₂(TpmPy)₂] (4), [ZnCl₂(TpmPy^Ph) ₂] (6) and [NiCl₂(TpmPy^Ph)₂] (7)). The reaction of (1) with VCl₃ gives [VOCl₂(TpmPy)] (8) that shows the N₃-pyrazolyl coordination-mode. Moreover, (1) and (2) react with cis-[PdCl₂(CH₃CN)₂] to give the disubstituted complexes [PdCl₂(TpmPy)₂] (9) and [PdCl ₂(TpmPy^Ph)₂] (10), respectively, bearing the scorpionate coordinated via the pyridyl group. Compounds (9) and (10) react with Fe(BF₄)₂ to give the heterobimetallic Pd/Fe systems [PdCl₂(μ-TpmPy)₂Fe](BF₄)₂ (11) and [PdCl₂(μ-TpmPy^Ph)₂Fe₂(H ₂O)₆](BF₄)₄ (13), respectively. Compound (11) can also be formed from reaction of (3) with cis-[PdCl ₂(CH₃CN)₂], while reaction of (3) with Cu(NO₃)₂ 2.5H₂O generates [Fe(μ-TpmPy) ₂Cu(NO₃)₂](BF₄)₂ (12), confirming the multidentate ability of the new chelating ligands. The X-ray diffraction analyses of compounds (1), (3), (4), (5), and (9) are also reported.