TY - JOUR
T1 - Evidence for Single-Electron Pathways in the Reaction between Palladium(II) Dialkyl Complexes and Alkyl Bromides under Thermal and Photoinduced Conditions
AU - Andersen, Thomas
AU - Kramer, Søren
AU - Overgaard, Jacob
AU - Skrydstrup, Troels
PY - 2017/6/12
Y1 - 2017/6/12
N2 - Palladium(II) dialkyl complexes have previously been studied for their formation of alkanes through reductive elimination. More recently, these complexes, especially L
2Pd(CH
2TMS)
2 derived from Pd(COD)(CH
2TMS)
2, have found general use as palladium(0) precursors for stoichiometric formation of oxidative addition complexes through a two-electron reductive elimination/oxidative addition sequence. Herein, we report evidence for an alternative pathway, proceeding through single-electron elementary steps, when DPEPhosPd(CH
2TMS)
2 is treated with an α-bromo-α,α-difluoroacetamide. This new pathway does not take place through a palladium(0) intermediate, neither does it afford the expected oxidative addition complexes. Instead, stoichiometric amounts of carbon-centered alkyl radicals are formed, which can be trapped in high yields either by TEMPO or by an arene, leading to α-aryl-α,α-difluoroacetamides. The same overall transformation takes place under both thermal conditions (70 °C) and irradiation with a household light bulb (at 30 °C). It is also demonstrated that DPEPhosPdMe
2, made in situ from Pd(TMEDA)Me
2, displays a similar initial reactivity. Finally, electronically and structurally different alkyl bromides were evaluated as reaction partners.
AB - Palladium(II) dialkyl complexes have previously been studied for their formation of alkanes through reductive elimination. More recently, these complexes, especially L
2Pd(CH
2TMS)
2 derived from Pd(COD)(CH
2TMS)
2, have found general use as palladium(0) precursors for stoichiometric formation of oxidative addition complexes through a two-electron reductive elimination/oxidative addition sequence. Herein, we report evidence for an alternative pathway, proceeding through single-electron elementary steps, when DPEPhosPd(CH
2TMS)
2 is treated with an α-bromo-α,α-difluoroacetamide. This new pathway does not take place through a palladium(0) intermediate, neither does it afford the expected oxidative addition complexes. Instead, stoichiometric amounts of carbon-centered alkyl radicals are formed, which can be trapped in high yields either by TEMPO or by an arene, leading to α-aryl-α,α-difluoroacetamides. The same overall transformation takes place under both thermal conditions (70 °C) and irradiation with a household light bulb (at 30 °C). It is also demonstrated that DPEPhosPdMe
2, made in situ from Pd(TMEDA)Me
2, displays a similar initial reactivity. Finally, electronically and structurally different alkyl bromides were evaluated as reaction partners.
UR - https://www.scopus.com/pages/publications/85020753671
U2 - 10.1021/acs.organomet.6b00893
DO - 10.1021/acs.organomet.6b00893
M3 - Journal article
SN - 0276-7333
VL - 36
SP - 2058
EP - 2066
JO - Organometallics
JF - Organometallics
IS - 11
ER -