Redox-Switchable Chiral Anions and Cations Based on Heteroatom-Fused Biferrocenes

Abstract

A new class of planar chiral heteroatom-bridged biferrocene species was prepared using (pR,pR,S S ,S S )-2,2″-bis(p-tolylsulfinyl)-1,1″-biferrocene (pR,pR,S S ,S S )-2 as a readily accessible precursor. Initially, one of the sulfinate groups in compound 2 is replaced with a trimethylstannyl or dimesitylboryl group. Replacement of the second sulfinate group with t-BuLi then results in cyclization to give the Me 2 Sn-bridged species (pS,pS)-4Sn and the Mes 2 B-bridged borate anion [(pS,pS)-4B] − . The products are redox active, as cyclic and square wave voltammetry data of (pS,pS)-4Sn and [Li(12-c-4) 2 ][(pS,pS)-4B] reveal two separate reversible oxidation events. The mixed-valent species [(pS,pS)-4Sn] + and (pS,pS)-4B can also be obtained by chemical oxidation with AgPF 6 or by simple exposure to air, respectively. A comparison of X-ray crystal structures reveals that the oxidized (mixed-valent) species contain distinct Fe(II) and Fe(III) sites, but UV−visible−NIR spectra display IVCT bands at ca. 4000 and 5000 cm −1 , indicative of electronic coupling in solution. All compounds are obtained in enantiomerically pure form, suggesting potential use as switchable chiral anions and cations.

Heteroatom-Bridged ortho-Biferrocenes: Stereoselective Synthesis, Structural Features, and Electrochemical Properties

“…12a,e While species C and D display inversion symmetry, the respective compounds with two different bridging elements are expected to be chiral. 15 Unsymmetric biferrocenes of this type are extremely rare, 16 and only very recently has the first enantiomerically pure heteroatom-bridged biferrocene been reported. Formal replacement of one of the borane moieties in D with phosphorus results in the unusual planar-chiral biferrocene E, which acts as an ambiphilic ligand whose electron-donating ability toward transition metals can be tuned by complexation of the Lewis acidic boryl moiety with a fluoride anion.…”

Directed Iron-Catalyzedortho-Alkylation and Arylation: Toward the Stereoselective Catalytic Synthesis of 1,2-Disubstituted Planar-Chiral Ferrocene Derivatives

“…Jackle et al succeeded in the stereoselective Negishi coupling and dimerization of a chiral ferrocenyl sulfoxide. 60 The formation of 20 represents the first example of a dehydrogenative dimerization of an ODG-substituted ferrocene derivative by C−H activation. Further investigations to improve the yield of 20 and to study the mechanistic details are currently underway.…”

“…The dehydrogenative dimerization of ODG-substituted arenes, e.g., under cobalt promotion or cobalt, palladium , or ruthenium catalysis, is well-known but unprecedented in ferrocene chemistry. Jäckle et al succeeded in the stereoselective Negishi coupling and dimerization of a chiral ferrocenyl sulfoxide . The formation of 20 represents the first example of a dehydrogenative dimerization of an ODG-substituted ferrocene derivative by C–H activation.…”

Recent Advances in π-Conjugated N^C-Chelate Organoboron Materials

“…In addition to the above-mentioned applications, other applications have been reported too. This includes the activation of small molecules [91,92], switchable chiral anions [93], NLO materials [94,95], among others. In a recent example, Wang et al [96] reported blue fluorescent polymers exhibiting thermally reversible photochromism.…”