76358-43-5Relevant articles and documents
Generation and Mesolysis of PhSeSiR3.-: Mechanistic Studies by Laser Flash Photolysis and Application for Bimolecular Group Transfer Radical Reactions
Pandey, Ganesh,Sesha Poleswara Rao,Palit,Mittal
, p. 3968 - 3978 (1998)
The investigation presented in this paper explores the mechanistic aspects and synthetic potentials of PET promoted reductive activation of selenosilane 1a to its radical anion 1a.-. PET activation of 1a is achieved through a photosystem comprising a light-absorbing electron-rich aromatic (ERA), such as DMN or DMA, as an electron donor and ascorbic acid as a co-oxidant. The evidence for the ET from excited singlet states of DMN as well as DMA to 1a is suggested by estimating negative ΔGet (-51 and -43.46 kcal mol-1, respectively) values and nearly diffusion- controlled fluorescence quenching rate constants (kqTR) 0.36 × 1010 M-1 s-1 and 0.28 × 1010 M-1 s-1, respectively, from time-resolved fluorescence quenching study. The transient absorption spectra of DMN.+, DMA.+, and 1a.- are obtained initially by pulse radiolysis in order to correlate the time- resolved absorption spectral data. Laser flash photolysis studies in the nanosecond time domain have confirmed the generation of 1a.-, DMN.+, and DMA.+, supporting the participation of the triplet state of DMN or DMA in the ET reaction. Mesolytic cleavage of 1a.- produced a silyl radical and a phenyl selenide anion. The preparative PET activation of 1a in acetonitrile in the presence of DMN or DMA leads to the formation of 5 and 6, confirming the fragmentation pattern of la.-. The overall ET rate constants (kr(DMN) = 0.99 × 1010 M-1 s-1 and kr(DMA) = 1.62 × 1010 M-1 s-1) and limiting quantum yields (φlim(DMN) = 0.034 and φlim(DMA) = 0.12) are estimated from the inverse plot (1/[1a] vs 1/φdis) obtained by measuring the dependence of photodissociation quantum yields of 1a at its maximum concentration in the presence of DMN or DMA. Silicon-centered radical species generated from the mesolysis of 1a.- are utilized for initiating a radical reaction by the abstraction of halogen atom from -C-X (X = Cl, Br) bonds, while PhSe-1 terminates the radical sequences via PhSeSePh. This concept is successfully applied for the bimolecular group transfer (BMGT) radical reactions and intermolecular radical chain addition reactions.
