Diaryliodonium salts (Ar-I⁺-Ar) react with certain phosphines (PZ₃) to form phosphonium salts (eq 1). When simple phosphines such as triphenylphosphine (Z = Ph₃P) and trimethyl phosphite (Z = OMe) are used the mechanism is a very efficient radical chain (eq 2-4) that allows fast photostimulated reactions to proceed.

Ar-I⁺-Ar + PZ₃ → ArP⁺Z₃ + Ar-I                                               (1)

Ar· + :PZ₃ → ArP·Z₃                                   Propagation            (2)                                 

ArP·Z₃ + Ar-I⁺-Ar → ArP⁺Z₃ + Ar-I·-Ar    Propagation            (3)

Ar-I·-Ar → ArI + Ar·                                  Propagation            (4)

This research studied the rate of reaction of phenyl radicals with tris(2,2,2-trifluoroethyl) phosphite (TFP) (eq 2, Z = OCH₂CF₃) and tris(trimethylsilyl) phosphite (TSP) (eq 2, Z = TMS). Competition experiments of TFP and TSP versus Ph₃P reacting with bis(4-tert- butylphenyl)iodonium hexafluorophosphate (BIH) were carried out and product ratios measured using ¹H 300 MHz NMR. We also carried out experiments to study the reactions of TFP and TSP with BIH in the absence of Ph₃P.  Mechanistic implications of the results will be discussed.