Extremely Electron‐Poor Bis(diarylmethylium)‐Substituted Ferrocenes and the First Peroxoferrocenophane

Abstract

We have prepared and studied extremely electron‐poor, deeply colored dicationic 1,1'‐bis(diarylmethylium)‐substituted ferrocenes [(η5‐C5H4‐CAr2)2Fe]2+ with various aryl substituents as their [B{C6H3(CF3)2‐3,5}4]– salts. Due to the strong acceptor substitution, the redox potential for the ferrocene‐based oxidation of the anisyl‐ or 2‐methylanisyl‐substituted congeners 1b2+ and 1c2+ is close to or even surpasses that of the second oxidation of parent ferrocene, i.e. the Cp2Fe+/2+ couple. The strongly Lewis‐acidic character of these complexes is manifest through strong interactions with donor solvents, which lead to a significant reduction of the intensities of the charge‐transfer bands in their electronic spectra and to solvatochromism. The reduced forms of the complexes tend to dimerize or oligomerize as revealed by EPR spectroscopy. Direduced 1b selectively reacts with molecular oxygen to form a peroxo‐bis(diarylmethyl)[4]ferrocenophane, which was also characterized by X‐ray crystallography.

Tailoring Valence Tautomerism by Using Redox Potentials: Studies on Ferrocene‐Based Triarylmethylium Dyes with Electron‐Poor Fluorenylium and Thioxanthylium Acceptors

“…In line with previous studies on similar ferrocenyl‐trityl radicals, [20–22] complexes 1 a . – 1 c .…”

“…In line with previous studies on similar ferrocenyl-trityl radicals, [20][21][22] complexes 1 a * -1 c * exhibit the exactly opposite behaviour. The middle bottom panel of Figure 9 shows this exemplarily for complex 1 c * ; graphical representations of the outcomes of such experiments on the other two reduced complexes are shown in Figure S37.…”

“…The ferrocene‐triarylmethylium dyads of our previous studies were conveniently generated from their carbinol precursors and Brookhart's acid, [31] which provides the very weakly coordinating [B{C 6 H 3 (CF 3 ) 2 } 4 ] − ([BArF 24 ] − ) counterion [32] . The latter was found to be crucial in order to stabilize these strong electrophiles [20–22] . The carbinol precursors 1 a ‐OH to 1 c ‐OH were synthesized from 4‐ferrocenylphenyl lithium and the respective fluorenone derivatives 6 a , 6 b [33] or the previously unknown 3,6‐bis(trifluoromethyl)‐9 H ‐thioxanthen‐9‐one, ( 5 ) according to Scheme 3.…”

“…Table 4), indicating that these carbinols are less electron‐rich than parent ferrocene or phenylferrocene ( E 1/2 0/+ =25 mV in CH 2 Cl 2 /NBu 4 + [PF 6 ] − ) [37] . The small influence of the different kinds of diarylmethyl pendants and their substituents (Me/MeO ( 1 a/1 b ); CF 3 /Me ( 1 c/1 d )) results from the quaternary, sp 3 ‐hybridized C‐OH connector, which cripples conjugation [20–22] …”

“…[37] The small influence of the different kinds of diarylmethyl pendants and their substituents (Me/MeO (1 a/1 b); CF 3 /Me (1 c/1 d)) results from the quaternary, sp 3 -hybridized C-OH connector, which cripples conjugation. [20][21][22] Figure 2 and Figures S23 to S26 show the voltammograms of the three new ferrocene-triarylmethylium dyads 1 a + -1 c + at a scan rate v of 100 mV/s. They all feature two redox waves, one for ferrocene oxidation and one for the reduction of the triarylmethylium acceptor.…”