Impact of O → S Exchange in Ferrocenyl Amides on the Structure and Redox Chemistry

The conformations and redox chemistry of ferrocenyl amides have been investigated in considerable depth in the last few years, while ferrocenyl thioamides have attracted less interest so far, although distinctly different conformations and reactivity patterns are expected. Monoferrocenyl amides Fc-NHC­(O)­CH₃ (<b>1</b>) and 1,1′-CH₃O­(O)­C-Fn-NHC­(O)­CH₃ (<b>2</b>) and diferrocenyl amides Fc-NHC­(O)-Fc (<b>5</b>) and Fc-NHC­(O)-Fn-NHC­(O)­CH₃ (<b>6</b>) are easily transformed into the corresponding thioamides (<b>3</b>, <b>4</b>, <b>7</b>, <b>8</b>) by treatment with Lawesson’s reagent (2,4-bis­(<i>p</i>-methoxyphenyl)-1,3-dithiaphosphetane-2,4-disulfide) (Fc = Fe­(C₅H₄)­(C₅H₅), Fn = Fe­(C₅H₄)₂). The thioamide conformations (<i>cis</i>/<i>trans</i>) in <b>3</b>, <b>4</b>, <b>7</b>, and <b>8</b> and the hydrogen bond determined secondary structure of dithioamide <b>8</b> have been elucidated by IR and NMR spectroscopy as well as by DFT calculations (B3LYP, LANL2DZ, PCM CH₂Cl₂) and contrasted with the corresponding amides <b>1</b>, <b>2</b>, <b>5</b>, and <b>6</b>. The electronic communication via the thioamide bridge in <b>7</b>^<b>+</b> and <b>8</b>^<b>+</b> in comparison to the interaction in the parent mixed-valence amides <b>5</b>^<b>+</b> and <b>6</b>^<b>+</b> has been probed by cyclic voltammetry, square wave voltammetry, UV/vis spectroelectrochemistry, EPR spectroscopy, and paramagnetic NMR spectroscopy. Additional chemical reactivity of the thioamide unit has been detected by electrochemical analysis