1,1 '-Bis(pyrazol-3-yl)ferrocene: A Clip Ligand That Forms Supramolecular Aggregates and Prismatic Hexanuclear Coinage Metal Complexes

Abstract

Two ferrocene derivatives with appended pyrazole sub stituents, namely, 1,1'-bis (5-methyl-1H-pyrazol-3-yl)ferrocene (H2LH) and 1,1'-bis(5-trifluoromethyl-1H-pyrazol-3-yl)ferrocene (H2LF), were synthesized. In solid state they form distinct H-bonded dimers with orthogonal (H2LH, C-2 symmetry) or antiparallel (H2LF, C-2/t symmetry) arrangement of the two ferrocene/pyrazole hybrid molecules. Supramolecular dimerization was also detected in solution at low temperatures, though diffusion-ordered spectroscopy and variable-temperature NMR spectroscopy revealed several dynamic processes. Redox potentials of the ferrocene derivatives are affected by the nature of the pyrazole substituent (Me, CF3). In their deprotonated form [L-R](2-), both ferrocene/pyrazole hybrids serve as ligands and form oligonudear Cu-I, Ag-I, and Au-I complexes that were identified by matrix-assisted laser desorption ionization mass spectrometry. X-ray crystallography revealed the structures of Cu6L3H and Ag6L3F, which both contain two parallel and eclipsed [M(mu-pz)](3) metallamacrocydes (M = Cu, Ag) linked by three ferrocene units. M-I center dot center dot center dot M-I distances between the two triangular M3N6 decks are shorter in Ag6L3F (3.28-3.30 vs 3.44-3.51 angstrom in the case of Cu6L3H), indicating substantial intramolecular closed-shell Ag(d(10))-Ag(d(10)) interactions. However, Cu6L3H features close intermolecular Cu center dot center dot center dot Cu contacts as short as 3.37 angstrom. Mossbauer data for both the ligands and complexes were collected, and electrochemical properties were measured; preliminary luminescence data are reported.