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Relevant academic research and scientific papers

Absolute rate constants for the reactions of primary alkyl radicals with aromatic amines

Hydrogen abstraction from diarylamines (4-X-C6H4)2NH [X = H, CH3, C8H17, CH3O, and Br] by the 2-methyl-2-phenylpropyl radical in n-dodecane solution was investigated by thermolysis of 3-methyl-3-phenylbutanoyl peroxide in the presence of various concentrations of the amines. The reaction is a non-chain process in which the 2-methyl-2-phenylpropyl radical and its rearrangement product, the 2-benzylpropan-2-yl radical, abstract hydrogen from both the solvent and the amine. Cross-disproportionation reactions of the rearranged radical led to the formation of significant amounts of β,β-dimethylstyrene. Rate constants for hydrogen abstraction by the unrearranged, primary alkyl radical from n-dodecane (k373K = 3.5 × 103 M-1 s-1), diphenylamine (k373K = 1.3 × 106 M-1 s-1), and the substituted diarylamines were determined from the product yields and the known rate constant for the radical rearrangement. From kinetic experiments with AT-deuteriodiphenylamine the deuterium kinetic isotope effect, kNH/kND, was found to be 2.3 at 373 K.

Probing Hydrogen Atom Transfer at a Phosphorus(V) Oxide Bond Using a "bulky Hydrogen Atom" Surrogate: Analogies to PCET

Recent computational studies suggest that the phosphate support in the commercial vanadium phosphate oxide (VPO) catalyst may play a critical role in initiating butane C-H bond activation through a mechanism termed reduction-coupled oxo activation (ROA) similar to proton-coupled electron transfer (PCET); however, no experimental evidence exists to support this mechanism. Herein, we present molecular model compounds, (Ph2N)3V=N-P(O)Ar2 (Ar = C6F5 (2a), Ph (2b)), which are reactive to both weak H atom donors and a Me3Si? (a "bulky hydrogen atom" surrogate) donor, 1,4-bis(trimethylsilyl)pyrazine. While the former reaction led to product decomposition, the latter resulted in the isolation of the reduced, silylated complexes (Ph2N)3V-N=P(OSiMe3)Ar2 (3a/b). Detailed analyses of possible reaction pathways, involving the isolation and full characterization of potential stepwise square-scheme intermediates, as well as the determination of minimum experimentally and computationally derived thermochemical values, are described. We find that stepwise electron transfer (ET) + silylium transfer (ST) or concerted EST mechanisms are most likely. This study provides the first experimental evidence supporting a ROA mechanism and may inform future studies in homogeneous or heterogeneous C-H activation chemistry, as well as open up a possible new avenue for main group/transition metal cooperative redox reactivity.

Picosecond Laser Photolysis Studies of Hydrogen Atom Transfer Reaction via Heteroexcimer State in Pyrene-Primary and Pirene-Secondary Aromatic Amine Systems: Role of "Hydrogen-Bonding" Interaction between Amino Group of Donor and ? Electron Acceptor in the Heteroexcimer

The mechanism of charge transfer followed by proton transfer in the hydrogen atom transfer reaction of excited pyrene-primary and -secondary amine systems has been directly demonstrated by means of a picosecond laser photolysis method.In the case of pyrene-N-ethylamine heteroexcimer system in hexane, for example, it has been observed that the 1-hydro-1-pyrenyl radical and the pyrene triplet state are produced simultaneously in the time region of subnanosecond to nanosecond.The deuteration of the NH group of the amine affects considerably the rate of formation of the 1-hydro-1-pyrenyl radical but not the rate of intersystem crossing from the heteroexcimer.On the basis of the results obtained for various pyrene-primary and -secondary aromatic amine heteroexcimer systems, the nature of the interaction between donor and acceptor in these heteroexcimers and their conformation in relation to the mechanism of the hydrogen atom transfer reaction via heteroexcimer have been elucidated.