Mercury-Free Preparation, Characterization, and Molecular Structure of Tricyanovinylferrocene Using an Unusual Reaction between Ferrocene and Tetracyanoethylene

A direct reaction between ferrocene (FcH) and tetracyanoethylene (TCNE) in various solvents and within a wide range of temperatures has been investigated in order to optimize the preparation of tricyanovinylferrocene. Under optimized reaction conditions, tricyanovinylferrocene was prepared in ∼26% yield along with cyanoferrocene as a major reaction product in the reaction between 1 equiv of FcH and 2 equiv of TCNE for 10 min in sulfolane at 110 °C. It was proposed that the reaction proceeds via a single-electron-transfer step, which results in the formation of a spectroscopically detected [FcH]•+[TCNE]•- intermediate followed by homolytic cleavage of the C−CN bond. The possible phase transition in tricyanovinylferrocene has been tested by X-ray crystallography at 173 and 293 K. The prominent visible band observed in the UV−vis spectrum of tricyanovinylferrocene has been unambiguously assigned to a metal-to-ligand charge-transfer transition on the basis of experimental and theoretical (TDDFT) data, while its solvatochromic behavior was tested using the Kamlet−Taft model. It has been found that the solvatochromism observed in tricyanovinylferrocene predominantly depends on the value of dipolarity/polarizability parameter π* in the Kamlet−Taft equation. The significant anisotropy of the quadrupole doublet in the Mössbauer spectra of tricyanovinylferrocene and cyanoferrocene was explained on the basis of DFT calculations.