Iron/2,6-Di(pyrazol-1-yl)pyridine Complexes with a Discotic Pattern of Alkyl or Alkynyl Substituents

Abstract

2,6-Di(4-iodopyrazol-1-yl)pyridine is converted to 2,6-di(4-{alkyn-1-yl}pyrazol-1-yl)pyridine (L1R; R’=CnH2n−3, n=12, 14, 16) derivatives by Sonogashira reactions. Hydrogenation of these intermediates yields the corresponding 2,6-di(4-alkylpyrazol-1-yl)pyridine (L2R; R=CnH2n+1) derivatives. Homoleptic Fe[BF4]2 complexes of all these ligands were prepared, bearing four long chain substituents in a discotic-type array. Crystallographic data from two L1R ligands imply the alkynyl substituents do not undergo intermolecular interdigitation in the solid state, which could explain the lower crystallinity and ill-defined spin-crossover in their iron complexes. Solid [Fe(L2R)2][BF4]2 (n=12 and 14) exhibit an irreversible, abrupt low→high-spin event near 350 K, which is not associated with solvent loss and may involve disordering of their alkyl chain conformations. No mesophase behavior was observed from any of these compounds.