Single Electron Delivery to Lewis Pairs: An Avenue to Anions by Small Molecule Activation

Abstract

Single electron transfer (SET) reactions are effected by the combination of a Lewis acid (e.g., E(CF) E = B or Al) with a small molecule substrate and decamethylferrocene (Cp*Fe). Initially, the corresponding reactions of (PhS) and (PhTe) were shown to give the species [Cp*Fe][PhSB(CF)] 1 and [Cp*Fe][(μ-PhS)(Al(CF))] 2 and [Cp*Fe][(μ-PhTe)(Al(CF))] 3, respectively. Analogous reactions with di-tert-butyl peroxide yielded [Cp*Fe][(μ-HO)(B(CF))] 4 with isobutene while with benzoyl peroxide afforded [Cp*Fe][PhC(O)OE(CF)] (E = B 5, Al 6). Evidence for a radical pathway was provided by the reaction of PhSnH and p-quinone afforded [Cp*Fe][HB(CF)] 7 and [Cp*Fe][(μ-OCH)(E(CF))] (E = B 8, Al 9). In addition, the reaction of TEMPO with Lewis acid and Cp*Fe afforded [Cp*Fe][(CHMeNOE(CF)] (E = B 10, Al 11). Finally, reactions with O, Se, Te and S gave [Cp*Fe][((CF)Al(μ-O)Al(CF))] 12, [Cp*Fe][((CF)Al(μ-Se)Al(CF))] 13, [Cp*Fe][(μ-Te)(Al(CF))] 14 and [Cp*Fe][(μ-S)B(CF))] 15, respectively. The mechanisms of these SET reactions are discussed, and the ramifications are considered.

Lewis Acid‐Mediated One‐Electron Reduction of Nitrous Oxide

“…The [Al 2 O 2 ] core with tetra‐coordinate Al centers shows average Al−O bond lengths of 1.831(1) Å, and Al‐O‐Al angles of 100.2(1)°. These values are comparable to those reported for other [Al 2 O 2 ] complexes . The Cp rings in the ferrocenyl moieties are slightly distorted with a dihedral angle of 4.2(2)°.…”

“…In contrast to Cp* 2 Co, Cp* 2 Fe is not able to convert B(C 6 F 5 ) 3 to its radical anion state due to thermodynamic mismatch (B(C 6 F 5 ) 3 was reported to have an E 1/2 of at least −1.52 vs. Fc/Fc + in CH 2 Cl 2 ) –. Still, this system is able to reduce O 2 to give a borane‐capped peroxide, and to reduce a range of chalcogen‐based small molecules …”

“…Stirring a mixture of Cp* 2 Fe and B(C 6 F 5 ) 3 in CH 2 Cl 2 under an atmosphere of N 2 O led to a slow color change from bright yellow to light green. The known compound (Cp* 2 Fe)[(μ‐HO)(B(C 6 F 5 ) 3 ) 2 ] ( 2 ) was isolated in 4 % yield after five days of reaction, while a large amount of unreacted starting material was identified in the rest of the mixture (Scheme ). The oxidation of Cp* 2 Fe into (Cp* 2 Fe) + and the generation of the μ‐HO anion are indicative of the N 2 O to O .− transformation.…”

“…, it reacts with another equivalent of [OAl(C 6 F 5 ) 3 ] .− , accompanied with arene transfer to free Al(C 6 F 5 ) 3 , yielding 5 along with [Al(C 6 F 5 ) 4 ] − . Attempts to isolate the salt (Cp 2 Fe)[Al(C 6 F 5 ) 4 ] were not successful, but similar arene transfer has been reported for reactions between (Cp* 2 Fe), Al(C 6 F 5 ) 3 , and a series of elemental chalcogens . Based on the experimental data, we cannot exclude the possibility that C−H activation is initiated by the dimeric [(F 5 C 6 ) 3 AlOAl(C 6 F 5 ) 3 ] .−[17] instead of by the monomeric [OAl(C 6 F 5 ) 3 ] .− .…”

Zinc‐Containing Radical Anions via Single Electron Transfer to Donor–Acceptor Adducts

“…[5] While FLPs are generally thought to effect heterolytic bond cleavages, in recent work we have shown that simple P/B FLPs can in some instances, react via single electron transfer (SET) reactions. [9] In very recent work, [10] we have extended this one-electron approach between [Cp* 2 Fe] and aL ewis acid ([E(C 6 F 5 ) 3 ], E= Bo rA l) to activate as eries of small molecules affording afamilyofu nique ferroceniums alts (Figure 1c). [6] In ar elatedw ork, Wang and co-workersd escribed one-electron oxidationo ft riarylamines by [B(C 6 F 5 ) 3 ]a ffording [·B(C 6 F 5 ) 3 ] À which was subsequently quenched by reaction with solvent.…”