Synthesis, characterization and crystal structure of 2-dicyanomethylene-1,3-bis(ferrocenylmethyl)-1,3-diazolidine

Abstract

By reaction of N,N′-ethylenebis(ferrocenylmethylamine)1 with tetracyanoethylene in dichloromethane the yellow compound 2-dicyanomethylene-1,3-bis(ferrocenylmethyl)-1,3-diazolidine 2 can be isolated. The single-crystal structure of 2 has been determined. It crystallizes in the non-centrosymmetric trigonal space group P3₂21, a= 12.255(2), c= 13.831(7)Å, Z= 3. Refinement of the atomic parameters by least-squares techniques gave a final R factor of 0.038 (R′= 0.034) for 1782 observed reflections having I > 2.5δ(I). Anomalous values of the bond distances and the vinyl carbon chemical shift in the ¹³C NMR spectrum of 2 are explained on the basis of a polarization due to a combination of the electron-donating behaviour of the nitrogen atoms with the electron-acceptor character of the cyano groups in the dicyanovinyl diamine fragment. The non-linear optical properties were investigated. A second harmonic generation signal for 2 was detected by powder techniques with a low efficiency. Electrochemical experiments in dimethyl sulfoxide revealed a two-electron diffusion-controlled oxidation process according to two consecutive one-electron steps involving the two ferrocenyl fragments the potentials of which are separated by 43 mV. A comproportionation constant K_c of 5.3 was found by differential pulse voltammetry, indicating that the mixed-valence species [Fe^IIIFe^II]⁺ is basically not stabilized.