ja0305712_si_001.pdf (1.92 MB)
Download fileThe Photochemistry of Polydonor-Substituted Phthalimides: Curtin-Hammett-Type Control of Competing Reactions of Potentially Interconverting Zwitterionic Biradical Intermediates
journal contribution
posted on 2004-02-04, 00:00 authored by Ung Chan Yoon, Hyuk Chul Kwon, Tae Gyung Hyung, Kyung Hwa Choi, Sun Wha Oh, Shaorong Yang, Zhiming Zhao, Patrick S. MarianoThe results of studies designed to obtain information about the factors that control the chemical
efficiencies/regioselectivities and quantum yields of single electron transfer (SET)-promoted reactions of
acceptor−polydonor systems are reported. Photochemical and photophysical investigations were carried
out with bis-donor tethered phthalimides and naphthalimides of general structure N-phthalimido- and
N-naphthalimido-CH2CH2-D-CH2CH2-NMsCH2-E (E = SiMe3 or CO2NBu4 and D = NMs, O, S, and NMe).
These substrates contain common terminal donor groups (NMsCH2SiMe3 or NMsCH2CO2NBu4) that have
known oxidation potentials and cation radical fragmentation rates. Oxidation potentials and fragmentation
rates at the other donor site in each of these substrates are varied by incorporating different heteroatoms
and/or substituents. Photoproduct distribution, reaction quantum yield, and fluorescence quantum yield
measurements were made. The results show that photocyclization reactions of α-trimethylsilylmethansulfonamide (E = SiMe3)- and α-carboxymethansulfonamide (E = CO2NBu4)-terminated phthalimides and
naphthalimides that contain internal sulfonamide, ether, and thioether donor sites (D = NMs, O, or S) are
chemically efficient (80−100%) and that they take place exclusively by a pathway involving sequential
photoinduced SET (zwitterionic biradical desilylation or decarboxylation) biradical cyclization. In contrast,
photoreactions of α-trimethylsilylmethansulfonamide- and α-carboxymethansulfonamide-terminated
phthalimides and naphthalimides that that contain an internal tertiary amine donor site (D = NMe) are
chemically inefficient and follow a pathway involving α-deprotonation at the tertiary amine radical cation
center in intermediate, iminium radical-containing, zwitterionic biradicals. In addition, the quantum efficiencies
for photoreactions of α-trimethylsilylmethansulfonamide- and α-carboxymethansulfonamide-terminated
phthalimides are dependent on the nature of the internal donor (eg., φ = 0.12 for D = NMs, E = SiMe3; φ
= 0.02 for D = S, E = SiMe3; φ = 0.04 for D = NMe, E = SiMe3). The results of this effort are discussed
in terms of how the relative energies of interconverting zwitterionic biradical intermediates and the energy
barriers for their α-heterolytic fragmentation reactions influence the chemical yields and quantum efficiencies
of SET promoted photocyclization reactions of acceptor−polydonor substrates.
History
Usage metrics
Read the peer-reviewed publication
Categories
Keywords
trimethylsilylmethansulfonamideamine donor sitesubstrateterminal donor groupsNMsCH 2 SiMe 3Interconverting Zwitterionic Biradical Intermediatesefficiencyzwitterionic biradical desilylationNMephotocyclization reactionsSiMe 3interconverting zwitterionic biradical intermediatesNMsCH 2 CO 2 NBu 4fragmentation ratesthioether donor sitesCO 2 NBu 4phthalimidequantum efficienciesnaphthalimide