Pyrazolyl Methyls Prescribe the Electronic Properties of Iron(II) Tetra(pyrazolyl)lutidine Chloride Complexes
A series of iron(ii) chloride complexes of pentadentate ligands related to α,α,α′,α′-tetra(pyrazolyl)-2,6-lutidine, pz 4lut, has been prepared to evaluate whether pyrazolyl substitution has any systematic impact on the electronic properties of the complexes. For this purpose, the new tetrakis(3,4,5-trimethylpyrazolyl)lutidine ligand, pz** 4lut, was prepared via a CoCl 2-catalyzed rearrangement reaction. The equimolar combination of ligand and FeCl 2 in methanol gives the appropriate 1:1 complexes [FeCl(pz R 4lut)]Cl that are each isolated in the solid state as a hygroscopic solvate. In solution, the iron(ii) complexes have been fully characterized by several spectroscopic methods and cyclic voltammetry. In the solid state, the complexes have been characterized by X-ray diffraction, and, in some cases, by Mössbauer spectroscopy. The Mössbauer studies show that the complexes remain high spin to 4 K and exclude spin-state changes as the cause of the surprising solid-state thermochromic properties of the complexes. Non-intuitive results of spectroscopic and structural studies showed that methyl substitution at the 3- and 5- positions of the pyrazolyl rings reduces the ligand field strength through steric effects whereas methyl substitution at the 4-position of the pyrazolyl rings increases the ligand field strength through inductive effects. © 2011 The Royal Society of Chemistry.
T. J. Morin and S. Wanniarachchi and C. Gwengo and V. Makura and H. M. Tatlock and S. V. Lindeman and B. Bennett and G. J. Long and F. Grandjean and J. R. Gardinier, "Pyrazolyl Methyls Prescribe the Electronic Properties of Iron(II) Tetra(pyrazolyl)lutidine Chloride Complexes," Dalton Transactions, Royal Society of Chemistry, Jan 2011.
The definitive version is available at http://dx.doi.org/10.1039/c1dt10712g
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