1,1′-Bis(pyrazol-4-yl)ferrocenes: Potential Clip Ligands and Their Supramolecular Structures

Abstract

Two ferrocene derivatives with pyrazoles appended at their C-4 position to both cyclopentadienyl (Cp) rings have been synthesized, namely, 1,1′-bis(1H-pyrazol-4-yl)ferrocene (H2HL) and 1,1′-bis(3,5-dimethyl-1H-pyrazol-4-yl)ferrocene (H2MeL). In the solid state, these are shown crystallographically to form supramolecular aggregates through intermolecular NH···N hydrogen bonds in either a dimeric (H2HL) or trimeric (H2MeL) arrangement. Variable-temperature NMR spectroscopy and diffusion-ordered spectroscopy (DOSY) evidenced the presence of [H2MeL]3trimers in [D8]toluene solution, whereas both H2HL and H2MeL exist as monomers in deuterated N,N-dimethylformamide ([D7]DMF) even at low temperatures. The kinetic parameters for the NH tautomerism have been determined. In their dianionic forms, both of these hybrid ferrocene/pyrazole molecules serve as ligands towards CuI, AgI, and AuIions. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) revealed the formation of [M2RL]3hexametallic complexes, the structures of which are suggested to have D3hsymmetry with two metallomacrocyclic [M(µ-pz)]3(pz = pyrazolate) decks connected by three ferrocene clips. Mössbauer spectra and preliminary luminescence data were collected for the proligands and the resulting complexes. Owing to the insolubility of the coinage-metal complexes, the electrochemical properties could be measured only for the two H2RL proligands.