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]3 trimers 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 AuI ions. Matrix‐assisted laser desorption/ionization mass spectrometry (MALDI MS) revealed the formation of [M2RL]3 hexametallic complexes, the structures of which are suggested to have D3h symmetry 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.