Electrosynthesis of Iminophosphoranes: Accessing P(V) Ligands from P(III) Phosphines

Abstract

Iminophosphorane P(V) compounds are accessed via electrochemical oxidation of commercially available P(III) ligands, including mono-, di- and tri-dentate phosphines as well as chiral phosphines. The reaction uses inexpensive bis(trimethylsilyl)carbodiimide as an efficient and safe aminating reagent. DFT calculations, cyclic voltammetry, and NMR spectroscopic studies provide insight into the reaction mechanism. The proposed mechanism based on the data reveals a special case of sequential paired electrolysis, namely a domino electrolysis process in which intermediates generated at the cathode are subsequently oxidized at the anode, followed by an additional convergent paired electrolysis process. DFT calculations of the frontier orbitals of the iminophosphorane are compared to those of the analogous P(III) phosphines and P(V) phosphine oxides. This reveals that N-cyano-iminophosphoranes have both a higher HOMO and lower LUMO than their analogous phosphine oxide, rendering them suitable for both sigma-donating and pi-back-bonding.

Overview of Recent Scale-Ups in Organic Electrosynthesis (2000–2023)

“…A range of additional transformations are emerging as opportunities toward scalable processes (e.g., electrochemical trifluoromethylation of heterocycles, hydrogenations − ) that may be of high interest to pharma. The electrosynthesis of catalysts , and ligands , for catalysis and the deployment of asymmetric electrocatalytic methods are also of interest, but examples of these on large scale are still scarce. The development of electrosynthetic processes in green solvents is also of interest.…”

Electrosynthesis of iminophosphoranes and applications in nickel catalysis

“…We have developed an operationally simple and safe electrochemical synthesis of new iminophosphorane ligands from commercially available phosphines. 66 A paired-electrolysis mechanism is operational where an electrogenerated base 67 triggers the formation of a key intermediate to enable a rare example of domino electrolysis. This synthetic method is safer than conventional Staudinger chemistry (herein we would have required the use of cyanogen-azide, NC–N 3 , which is extremely hazardous due to its energetic nature, in fact it is a primary explosive).…”

Electrosynthesis of Aryliminophosphoranes in Continuous Flow

“…In conclusion, our study has successfully established a robust and scalable protocol for the flow electrosynthesis of aryliminophosphoranes. [15] Importantly, our methodology stands out when compared to previously reported approaches for synthesizing these compounds. [16] Our method also eliminates the need for the use of harmful or hazardous reagents, such as azides and molecular bromine, and operates smoothly at room temperature.…”