Mechanism of dediazoniation of arenediazonium salts with triphenylphosphine and trialkyl phosphites. Generation of cation radicals from trivalent phosphorus compounds and their reactions

Abstract

4-Nitro-, 4-methyl-, and 4-methoxy-benzenediazonium fluoroborates are readily dediazoniated with triphenylphosphine or trialkyl phosphites (alkyl = methyl or ethyl) in alcoholic solvents at room temperature in the dark under a nitrogen atmosphere to give the corresponding arenes and the corresponding oxidation product from the phosphine or the phosphites, triphenylphosphine oxide or trialkyl phosphates, respectively, along with a small amount of biaryls. In the reaction with the phosphite, dialkyl arylphosphonate is also formed. The stoichiometry of the reactions and the results of the reactions in deuteriated methanols, together with other evidence, indicate that the reactions proceed by a radial-chain mechanism initiated by single-electron transfer from the trivalent phosphorus compound to the diazonium salt, during which the cation radical is generated from the former. The product distribution shows that this cation radical reacts with the solvent alcohol to give a phosphoranyl radical, which eventually affords the final product, the phosphine oxide or the phosphate, from the phosphine or the phosphite, respectively. The cation radical from the phosphite also undergoes radical coupling with the aryl radical Ar' generated during the reaction to yield dialkyl arylphosphonate via a phosphonium intermediate, whereas no radical coupling of the cation radical from the phosphine with Ar' takes place.

An Efficient Procedure for the Synthesis of Crystalline Aryldiazonium Trifluoroacetates – Synthetic Applications

“…In particular, bases (such as tertiary amines, carboxylates, or carbonates) better suited for our synthetic purposes. However, the use of N 2 or Ar is recommended because of the known sensi-as well as phosphanes [57] are known to react rapidly with diazonium salts at the β-nitrogen atom, thereby initiating tivity of organopalladium species to air. The use of trifluoroacetate salts led to a reduction in the reaction times at radical chain reactions.…”

Aryldiazonium Salts as Nitrogen‐Based Lewis Acids: Facile Synthesis of Tuneable Azophosphonium Salts

“…[11] Surprisingly,t o date the corresponding azoammonium salts [RN 2 (NR 3 )][X] are unknown, [12] while the phosphine-diazonium Lewis adducts have been barely studied. [15,16] Flower and co-workers synthesized B,b ut only reported its 31 PNMR resonance (d 31 P{ 1 H} = 40 ppm;R= 6-naphthalen-2-ol), [17] and Wokaun and co-workers characterized C only spectroscopically (R = Cl, CN,S O 2 NH 2 ,C (O)OEt;F igure 2). [14] Later, Yasui and co-workers found that aryldiazonium tetrafluoroborates are readily dediazoniated by triphenylphosphine by single-electron transfer when mixed in alcoholic solvents at room temperature.…”

Enantioselective Heck–Matsuda Arylations through Chiral Anion Phase‐Transfer of Aryl Diazonium Salts

“…[5] However, enantioselective variants of the Heck–Matsuda reaction are rare, largely because commonly employed chiral phosphine ligands are incompatible with diazonium salts. [6] …”