1,3-Diketonatoboron difluoride sensitized cation radical reactions

Chow, Yuan L.; Xiang, Cheng

doi:10.1139/v91-198

Cited by 22 publications

(13 citation statements)

References 14 publications

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“…The primary product is assumed to be formed by a [2+2] photocycloaddition to a BF2 complex to form a cyclobutane derivative 16 (see Scheme 1); the ring opening and hydrolysis should give 1,5-diketone 17 (or 10 or 13). This mechanism is proposed in analogy to the photoaddition of dibenzoylmethanatoboron difluoride to olefins (3). The hydrolysis of the BF, moiety generates hydrofluoric acid, which promotes acid-catalyzed reactions to be described below.…”

Section: Discussionmentioning

confidence: 99%

“…Using dibenzoylmethanatoboron difluoride (DBMBF,) as a model, we have described the photocycloaddition with some olefins; such a reaction is shown to be regiospecific and highly stereoselective. Further, its mechanism is shown to be highly unusual in involving the excimer of DBMBF, (3). While DBMBF, does not photolytically add to benzene derivatives, we have been surprised to observe that alkyl-type 1,3-diketonatoboron difluorides photolytically add to benzene derivatives.…”

mentioning

confidence: 87%

“…We have demonstrated that the singlet excited state of 1,3-diketonatoboron difluorides undergoes photocycloaddition of the diketone moiety to simple olefins, and also sensitizes various electron rich olefins to undergo cation radical reactions (1)(2)(3). The primary reaction of the BF, complexes has been suggested to involve some degree of electron transfer from excited substrates, as indicated by a correlation of log k, (where k, is the quenching rate constant of a BF, complex fluorescence) and ionization potentials of substrates (1).…”

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confidence: 99%

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The photoaddition of 1,3-diketonatoboron difluorides with benzene derivatives

Chow¹,

Ouyang²

1991

Can. J. Chem.

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The boron difluoride complexes of 2-acetylcyclohexanone, 2-acetylcyclopentanone, and acetylacetone (abbreviated as ACHBF2, ACPBF2, and AABF2) were irradiated in the presence of benzene to give the 1:1 adducts as the primary photoadducts; for certain BF2 complexes, toluene, chlorobenzene, benzonitrile, and methyl benzoate were also used as substrates. The 1,5-diketone photoadducts were assumed to form by a [2+2] photocycloaddition followed by cyclobutane opening and hydrolysis to give 1,2 adducts. They undergo a variety of secondary thermal reactions, probably acid catalyzed, to give enol ethers, enol acetates, acetophenones, and ketonylacetophenones. The efficiency of these secondary reactions determines the final products. Photoaddition with a monosubstituted benzene preferentially occurs at the 3,4 bond without regioselectivity. Under oxygen, ACHBF2 photolytically reacts with benzene to give a secondary oxidation product of a 10-membered cyclic alkylphe-none, which is proven by X-ray crystallographic analysis to have the benzene ring and carbonyl group in orthogonal orientation. It is shown that the singlet excited state ACHBF2 initiates the photoaddition, probably through the formation of the benzene exciplex, which could be detected by its emission. While the Stern–Volmer rates are small, the quantum yield of photoaddition products is as high as 0.12–0.19 under limiting conditions. Key words: [2+2] photocycloaddition, non-planar alkanophenone, macrocyclic alkanophenone, boron difluoride complexes, photoaddition to benzenes.

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Section: Discussionmentioning

confidence: 99%

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confidence: 87%

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confidence: 99%

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The photoaddition of 1,3-diketonatoboron difluorides with benzene derivatives

Chow¹,

Ouyang²

1991

Can. J. Chem.

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“…BF 2 bdks in their singlet‐excited state undergo photocycloaddition with alkenes and arenes; therefore, they can serve as starting compounds for the synthesis of 1,5‐diketones . BF 2 bdks are used in the design of a new polymethine dye with intense long‐wavelength absorption .…”

Section: Introductionmentioning

confidence: 99%

“…INTRODUCTION synthesis of 1,5-diketones [27][28][29][30][31][32][33][34]. BF 2 bdks are used in the design of a new polymethine dye with intense long-wavelength absorption [35,36].…”

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confidence: 99%

Synthesis and Photophysical Properties of Alkoxysilyl Derivatives of Dibenzoylmethanatoboron Difluoride

et al. 2013

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Alkoxysilyl derivatives of dibenzoylmethanatoboron difluoride (DBMBF2) are synthesized by the hydrosilylation reaction of the corresponding O‐allyl derivatives of DBMBF2 with triethoxysilane. The photophysical properties of the synthesized O‐allyl and alkoxysilyl derivatives are investigated. It is found that the absorption and fluorescence spectra of the DBMBF2 derivatives essentially depend on the position of the O‐allyl or O‐propyl alkoxysilyl substituent. The highest fluorescence quantum yield is obtained for the para‐position, whereas the substitution at the meta‐position gives the largest bathochromic shift in the fluorescence spectrum. Density functional theory calculations of the structures and time‐dependent density functional theory calculations of the gas‐phase excitation and emission energies of alkoxysilyl derivatives are performed at the PBE0/SVP level of theory. Some spectral features of para‐, ortho‐, and meta‐substituted derivatives can be adequately explained by the overlapping of two absorption bands.

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The Structure and Decay Dynamics of Exciplexes Derived from Dibenzoylmethanatoboron Difluoride and Alkylbenzenes in Cyclohexane

Chow

Liu

Johansson

et al. 2000

Chemistry A European J

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Dibenzomethanatoboron difluoride (DBMBF2) interacted with alkylbenzenes from its singlet excited state to form exciplexes ranging from weak polarity up to contact radical ion pairs (CRIP); this exciplex series shows the characteristics in the Marcus "normal" region. In cyclohexane these exciplexes gave intense fluorescence spectra and high quantum yields (phi(infinity)ex). The dipole moment of these exciplexes calculated from the solvatochromic shift of the fluorescence maximums (vmax) was used to estimate the coefficient ("a" and "c") of the CT and LE terms in the exciplex wavefunction. On the basis of the measured lifetimes and phi(infinity)ex of these exciplexes, the radiative (k(ex)f) and nonradiative (k(ex)NR) rate constants were calculated. The former k(ex)f were also computed from a semi-empirical approach based on the assumption that the exciplex wavefunction could be adequately described by CT and LE states, and that *DBMBF2 primarily contributes to the probability of exciplex emission. Two results agree with each other with small systematic deviations for those less polar exciplexes. The plots of k(ex)r and k(ex)NR (or their logarithmic value) against the LE contribution (c2) and transition energy gaps (hvmax) afford better correlation than those against -deltaG(-et). This indicates the role played by the LE contribution in generating the stabilization energy (U(s)) in these exciplexes through the A-D+)<==> *AD) resonance interaction; U(s), in turn, modifies -deltaG(-et) to afford the decay driving force hvmax. Also, those plots from k(ex)f values (being determined directly from experiments) show better correlation than those from k(ex)NR. In contrast to the CRIP type exciplexes in the Marcus "inverted" region, these k(ex)f and k(ex)NR increase in the common trend with increasing transition energy gaps. The k(ex)NR plots show less steep slopes and attains more quickly a minimum toward the CRIP region; the latter is identified as the turning point from the "normal" to "inverted" region. Both the attenuation and reversal of the k(ex)NR value with increasing polarity are believed to be generated by the emerging contribution of the intersystem crossing process as an additional nonradiative process, which is induced by the increased spin-orbit coupling in highly polar exciplexes.

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1,3-Diketonatoboron difluoride sensitized cation radical reactions

Cited by 22 publications

References 14 publications

The photoaddition of 1,3-diketonatoboron difluorides with benzene derivatives

The photoaddition of 1,3-diketonatoboron difluorides with benzene derivatives

Synthesis and Photophysical Properties of Alkoxysilyl Derivatives of Dibenzoylmethanatoboron Difluoride

The Structure and Decay Dynamics of Exciplexes Derived from Dibenzoylmethanatoboron Difluoride and Alkylbenzenes in Cyclohexane

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