Abstract
Voltammetry provides important information on the redox properties of catalysts (transition metal complexes of Ni, Co, Mn, etc.) and their activity in electrocatalytic reactions of aromatic C–H phosphonation in the presence of a phosphorus precursor, for example, dialkyl-H-phosphonate. Based on catalytic current growth of oxidation or reduction of the metal catalysts (CoII, MnII, NiII, MnII/NiII, MnII/CoII, and CoII/NiII), quantitative characteristics of the regeneration of catalysts were determined, for example, for MnII, NiII and MnII/NiII, CoII/NiII pairs. Calculations confirmed the previously made synthetic observations on the synergistic effect of certain metal ions in binary catalytic systems (MnIIbpy/NiIIbpy and NiIIbpy/CoIIbpy); for mixtures, the observed rate constants, or TOF, were 690 s−1 and 721 s−1, respectively, and product yields were higher for monometallic catalytic systems (up to 71% for bimetallic catalytic systems and ~30% for monometallic catalytic systems). In some cases, the appearance of pre-waves after adding H-phosphonates confirmed the preceding chemical reaction. It also confirmed the formation of metal phosphonates in the time scale of voltammetry, oxidizing or reducing at lower potentials than the original (RO)2P(O)H and metal complex, which could be used for fast diagnostics of metal ion and dialkyl-H-phosphonate interactions. Electrochemical transfer of an electron to (from) metal phosphonate generates a phosphonyl radical, which can then react with different arenes to give the products of aromatic C–H phosphonation.
Highlights
IntroductionOrganophosphorus compounds with P–C bonds containing a phosphonate group P(O)(OAlk) or phosphonic acid R–PO(OH) residues are an important class of substrates because they have broad applications in various areas of human livelihood [8,9,10,11,12]
A highly single-electron step catalysis is that cyclic voltammetry (CV)
We we proposed proposed an an electrocatalytic electrocatalytic approach approach for for the the phosphonation phosphonation of of aromatic, aromatic, Earlier, heteroaromatic, and heterocyclic compounds in one stage using transition metal complexes and heteroaromatic, and heterocyclic compounds in one stage using transition metal complexes and salts salts as catalysts
Summary
Organophosphorus compounds with P–C bonds containing a phosphonate group P(O)(OAlk) or phosphonic acid R–PO(OH) residues are an important class of substrates because they have broad applications in various areas of human livelihood [8,9,10,11,12]. Researchers have been increasingly interested in direct phosphonation of aromatic compounds (benzene derivatives, N,N-dialkylbenzamides and nitrobenzene, substituted furans, thiophenes, thiazoles and pyrroles, pyridines and derivatives, etc.) [2,3,13,14,15] by C–H/P–H cross-coupling with dialkyl-H-phosphonates and diaryl phosphine oxides [16] during radical initiation of the process or under catalysis of the metal complex (Scheme 1).
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