This paper describes
the one-electron interconversions of isolable
NiIII and NiIV complexes through their reactions
with carbon-centered radicals (R•). First, model NiIII complexes are shown to react with alkyl and aryl radicals to afford
NiIV products. Preliminary mechanistic studies implicate
a pathway involving direct addition of a carbon-centered radical to
the NiIII center. This is directly analogous to the known
reactivity of NiII complexes with R•, a step that
is commonly implicated in catalysis. Second, a NiIV–CH3 complex is shown to react with aryl and alkyl radicals to
afford C–C bonds via a proposed SH2-type mechanism.
This pathway is leveraged to enable challenging H3C–CF3 bond formation under mild conditions. Overall, these investigations
suggest that NiII/III/IV sequences may be viable redox
pathways in high-oxidation-state nickel catalysis.
This Communication describes studies of Ph-R (R = CF or CFCF) coupling at Pd complexes of general structure (PBu)Pd(Ph)(R). The CF analogue participates in fast Ph-CF coupling (<5 min at 80 °C). However, the formation of side products limits the yield of this transformation as well as its translation to catalysis. DFT and experimental studies suggest that the side products derive from facile α-fluoride elimination at the 3-coordinate Pd complex. Furthermore, they show that this undesired pathway can be circumvented by changing from a CF to a CFCF ligand. Ultimately, the insights gained from stoichiometric studies enabled the identification of Pd(PBu) as a catalyst for the Pd-catalyzed cross-coupling of aryl bromides with TMSCFCF to afford pentafluoroethylated arenes.
This article describes a detailed investigation of ligand effects on Ph−CF 3 coupling from phosphinoferroceneligated Pd II (Ph)(CF 3 ) complexes. This study reveals that increasing the size of the phosphine substituents results in an enhanced rate of Ph−CF 3 coupling, with (D t BPF)Pd(Ph)-(CF 3 ) (D t BPF = 1,1′-bis(di-tert-butylphosphino)ferrocene) being the most reactive complex. The mechanism of Ph−CF 3 bond formation from both (D t BPF)Pd(Ph)(CF 3 ) and (D i PrPF)Pd(Ph)(CF 3 ) (D i PrPF = 1,1′-bis(diisopropylphosphino)ferrocene) was interrogated experimentally and computationally. These studies implicate a pathway involving concerted Ph−CF 3 bond-forming reductive elimination from the fourcoordinate Pd II centers. An alternative pathway involving α-fluoride elimination and subsequent PhF 2 C−F coupling from Pd II (CF 2 Ph)(F) intermediates was also evaluated but was ruled out based on DFT as well as the independent synthesis and reactivity studies of (D i PrPF)Pd(CF 2 Ph)(F).
A method for the room temperature deoxyfluorination of benzaldehydes and α-ketoesters using sulfuryl fluoride and Me 4 NF is described. A large scope of aryl and heteroaryl substrates is demonstrated, and this method compares favorably to other common deoxyfluorination methods for many substrates.
An isolable pyridinium trifluoromethoxide
salt is prepared from
the reaction of 4-dimethylaminopyridine with the commercially available
liquid 2,4-dinitro(trifluoromethoxy)benzene. The salt is an effective
trifluoromethoxide source for SN2 reactions to form trifluoromethyl
ethers.
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