Base‐Free Generation of Organic Electron Donors from Air‐Stable Precursors

Abstract

Organic electron donors (OEDs) are powerful reducing agents recognized for their potential in the reduction of challenging substrates and in original applications. Nonetheless, their low stability in atmospheric oxygen or over time complicates their manipulation and storage. To overcome these constraints and enhance OED practicality, new air- and moisture-stable aminopyridinium carboxylate and carbonate precursors were synthesized and thermally activated to generate the potent electron donor in situ. Carboxylate adducts proved to be excellent latent OED systems, enabling the facile and efficient reduction of challenging substrates. Their reduction properties were correlated to their structural characteristics by thermogravimetric and spectroscopic analysis.

Comprehensive Basicity Scales for N‐Heterocyclic Carbenes in DMSO: Implications on the Stabilities of N‐Heterocyclic Carbene and CO2 Adducts

“…With the established acidity scales for ac omprehensive scope of commonly seen NHCPsa th and, we envisaged that these thermodynamic data of NHCs may be of useful to investigate the stabilities of NHC-CO 2 adducts which have been extensively used as the surrogates for NHCs in the organic syntheses. [29] The establishment of LFERs between the calculated CO 2 binding energies (DG r )a nd the related physicochemical parameters of anions of ionic liquids or gas phasea cidities of NHCPs for the purpose of assessingt he stability of the related CO 2 adducts have been practiced previously. [30] Along this line, the changes of the Gibbs energies[ DG r ,E q.…”

Guanidines as Reagents in Proton-Coupled Electron-Transfer Reactions and Redox Catalysts

“…60 Very recently, air-stable precursors of these electron donors were developed. 61 All the nitrogen electron donors in Figure 1 are extremely weak Brønsted bases. Therefore, they can only be applied in proton-coupled electron-transfer reactions if a Brønsted base is added as additional reaction partner.…”

Bis(Iminophosphorano)‐Substituted Pyridinium Ions and their Corresponding Bispyridinylidene Organic Electron Donors

“…Although various bispyridinylidene derivatives have been isolated, [40,52] they are most conveniently generated in situ owing to their extreme air‐sensitivity [8] . In our hands, attempts to isolate 3PhCy , 3CyPh and 3CyCy in pure form were not successful.…”

“…OEDs have found application in polymerizations, [1] in desulfurization of hydrocarbons from crude oil, [2] and in the conversion of greenhouse gas SF 6 into useful fluorinating agents [3] . The strongly donating neutral compounds are also effective homogeneous reducing agents, [4–8] as demonstrated by their ability to reduce substrates such as aryl halides, [9–13] sulfones and arenesulfonamides, [12,14] Weinreb amides, [15] acyloin derivatives, [16] triflates and triflamides, [17] nitroarenes, [18,19] thioacetals and thioethers, [20] and reductive coupling of benzyl halides to aldehydes [21] . With photoactivation, the electron donor strength is further enhanced, and substrates such as aryl fluorides, [22] activated benzenes, [23] N,N‐dialkyl arenesulfonamides, [24] benzylic esters and ethers, [25] benzyl malonates and cyanoacetates, [26] and malononitriles [27] have been reduced.…”