Nitrogen‐Based Lewis Acids Derived from Phosphonium Diazo Cations

Abstract

Reaction of PPh3 and [(p‐ClC6H4)N2][BF4] affords [(p‐ClC6H4)N(PPh3)N(PPh3)][BF4] 1, while reaction with (Ph2PCH2)2 gave [(p‐ClC6H4)(NPh2PCH2)2)][BF4] 2. These species confirm the Lewis acidity of [(p‐ClC6H4)N2(PR3)][BF4] cations at N. In contrast, use of bulky phosphines afford the species [ArN2(PR3)][BF4] (R=tBu 3, Mes 4). Compound 3 undergoes one electron reduction to give the stable radical [(p‐ClC6H4)N2(PtBu3)]. 5. Combination of 3 and PtBu3 acts as an FLP to effect (SPh)2 cleavage, generating [PhSPtBu3]+ and the radical [ArN2(PR3)].. Collectively, these data affirm the ability of the cations [ArN2(PR3)]+ to behave as one or two electron acceptors.

Establishing the Role of Triflate Anions in H2 Activation by a Cationic Triorganotin(IV) Lewis Acid

“… 8 Important exceptions are “frustrated radical pairs”, which activate substrates via single electron pathways. 9 Recently, the range of LAs displaying FLP-like reactivity has expanded to encompass a number of cationic species (or neutral species that act as surrogates for the active cationic LA) based on B(III), 10 Si(IV), 11 C(IV), 12 N(III), 13 P(V), 14 and Sb(V). 15 , 16 …”

Recent Advances in Group 14 and 15 Lewis Acids for Frustrated Lewis Pair Chemistry

“…Furthermore, N‐based Lewis acids derived from diazonium cations are also explored [72] when Stephan and coworkers performed a reaction between diazonium salt [(p‐ClC 6 H 4 )N 2 ][BF 4 ] with one equivalent of base PR 3 (R=Ph, tBu, Mes) (Scheme 28). The resulting phosphonium diazo salts act as one electron acceptors.…”

Diazonium Salts as Nitrogen-Based Lewis Acids

“…The high tuneability of the diazonium salt directly relates to the color of the azophosphonium salt, which can be substantiated by UV/Vis spectroscopy, revealing two absorption bands from  abs = 303-464 nm (→*) and  abs = 453-523 nm (n→*). 33 Further reaction of [(p-Cl-C 6 H 4 )N 2 (PMes 3 )][BF 4 ] with addition of 1 equivalent of tBu 3 P resulted in the liberation of Mes 3 P and showed clean addition of tBu 3 P, presumably because of the greater Lewis basicity of the latter. Note, addition of 1 equivalent of the less bulky Ph 3 P leads to the unstable species [(p-R-C 6 H 4 )N 2 (PPh 3 )][BF 4 ] (R = H, 32 Cl 33 ) and, upon addition of 2 equivalents, bis-addition is observed, resulting in the addition of the phosphine to both nitrogen atoms in a pseudotransoid disposition forming [(p-Cl-C 6 H 4 )N(PPh 3 )N(PPh 3 )][BF 4 ], 33 highlighting the necessity of bulky groups on the phosphine for controlled mono-addition.…”

“…Stephan and co-workers demonstrated that the formed azophosphonium salt could be used in follow-up chemistry forming a radical species (Scheme 19). 33 Dissolving the azophosphonium salt 30 with tBu 3 P in CH 2 Cl 2 gave an immediate color change of the solution to dark-red/brown upon addition of diphenyl disulfide. EPR spectroscopy indicated the formation of a paramagnetic species 31 [(p-Cl-C 6 H 4 )N 2 (Pt-Bu 3 )] • , which could also be formed by reacting the azophosphonium salt directly with PhSNa, potassium metal or Cp 2 -Co.…”

“…Stephan and co-workers reported on the analogy of their azophosphonium radical species to these azoimidazolium radical species, indicating both class of compounds have similar EPR spectra. 33,45 Moreover, both azo compounds can be reversibly reduced to their corresponding aminyl radical species and both reductions can be performed with potassium as reducing agent.…”