Synthesis, structure, and electrochemical properties of 4,5-diaryl-1,2,3-triphosphaferrocenes and the first example of multi(phosphaferrocene)

Abstract

The reaction between aryl substituted sodium 1,2,3-triphospholides or disodium bis(1,2,3-triphospholide) and [Fe(η⁶-(C₆H₅CH₃)Cp]⁺[PF₆]⁻ in boiling diglyme results in pure 1,2,3-triphosphaferrocenes 1–3 or bis(1,2,3-triphosphaferrocene) 4, respectively, in good yields. The structure of all obtained 1,2,3-triphosphaferrocenes 1–4 has been extensively studied experimentally (NMR, UV-Vis spectroscopy, and X-ray analysis for 1 and 4) and quantum chemically. The electrochemical properties of 1,2,3-triphosphaferrocenes 1–4 in the solid state were studied for the first time and a reversible one-electron oxidation (E_1/2 = 0.52–0.92 V vs. Fc⁺/Fc) was demonstrated for 1, 3, and 4. In the case of 1,4-bis(5-phenyl-4-(1,2,3-triphospaferrocenyl))benzene 4, consecutive oxidation in the solid state is observed in contrast to other 1,2,3-triphosphaferrocenes 1–3. According to the ESR data, the g-factor of the oxidized bis(1,2,3-triphosphaferrocene), 4 (g = 2.12) is different from the g-factors of oxidized 1,2,3-triphosphaferrocenes 1–3 (g = 2.01). This is the first example of multi(ferrocenyl) systems based on the phosphaferrocene motif, which in turn opens up a new fundamental platform for the preparation of compounds with stimuli-responsive properties.