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Methylbismuth: an organometallic bismuthinidene biradical.

ABSTRACT: We report the generation, spectroscopic characterization, and computational analysis of the first free (non-stabilized) organometallic bismuthinidene, BiMe. The title compound was generated in situ from BiMe3 by controlled homolytic Bi-C bond cleavage in the gas phase. Its electronic structure was characterized by a combination of photoion mass-selected threshold photoelectron spectroscopy and DFT as well as multi-reference computations. A triplet ground state was identified and an ionization energy (IE) of 7.88 eV was experimentally determined. Methyl abstraction from BiMe3 to give [BiMe2]• is a key step in the generation of BiMe. We reaveal a bond dissociation energy of 210 ± 7 kJ mol-1, which is substantially higher than the previously accepted value. Nevertheless, the homolytic cleavage of Me-BiMe2 bonds could be achieved at moderate temperatures (60-120 °C) in the condensed phase, suggesting that [BiMe2]• and BiMe are accessible as reactive intermediates under these conditions.

SUBMITTER: Mukhopadhyay DP

PROVIDER: S-EPMC7450715 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature

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Methylbismuth: an organometallic bismuthinidene biradical.

Mukhopadhyay Deb Pratim DP Schleier Domenik D Wirsing Sara S Ramler Jacqueline J Kaiser Dustin D Reusch Engelbert E Hemberger Patrick P Preitschopf Tobias T Krummenacher Ivo I Engels Bernd B Fischer Ingo I Lichtenberg Crispin C

Chemical science 20200603 29

We report the generation, spectroscopic characterization, and computational analysis of the first free (non-stabilized) organometallic bismuthinidene, BiMe. The title compound was generated <i>in situ</i> from BiMe<sub>3</sub> by controlled homolytic Bi-C bond cleavage in the gas phase. Its electronic structure was characterized by a combination of photoion mass-selected threshold photoelectron spectroscopy and DFT as well as multi-reference computations. A triplet ground state was identified an ...[more]

PMID: 32874526

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Project description:Cholesterol (Ch) is an important lipidic building block and a target for oxidative degradation, which can be induced via free radicals or singlet oxygen ((1)O2). Suprofen (SP) is a nonsteroidal anti-inflammatory drug that contains the 2-benzoylthiophene (BZT) chromophore and has a ?,?* lowest triplet excited state. In the present work, dyads (S)- and (R)-SP-?-Ch (1 and 2), as well as (S)-SP-?-Ch (3) have been prepared from ?- or ?-Ch and SP to investigate the possible competition between photogeneration of biradicals and (1)O2, the key mechanistic steps in Ch photooxidation. Steady-state irradiation of 1 and 2 was performed in dichloromethane, under nitrogen, through Pyrex, using a 400 W medium pressure mercury lamp. The spectral analysis of the separated fractions revealed formation of two photoproducts 4 and 5, respectively. By contrast, under the same conditions, 3 did not give rise to any isolable Ch-derived product. These results point to an intramolecular hydrogen abstraction in 1 and 2 from the C7 position of Ch and subsequent C-C coupling of the generated biradicals. Interestingly, 2 was significantly more photoreactive than 1 indicating a clear stereodifferentiation in the photochemical behavior. Transient absorption spectra obtained for 1-3 were very similar and matched that described for the SP triplet excited state (typical bands with maxima at ca. 350 nm and 600 nm). Direct kinetic analysis of the decay traces at 620 nm led to determination of triplet lifetimes that were ca. 4.1 ?s for 1 and 2 and 5.8 ?s for 3. From these data, the intramolecular quenching rate constants in 1 and 2 were determined as 0.78 × 10(5) s(-1). The capability of dyads 1-3 to photosensitize the production of singlet oxygen was assessed by time-resolved near infrared emission studies in dichloromethane using perinaphthenone as standard. The quantum yields (??) were 0.52 for 1 and 2 and 0.56 for 3. In conclusion, SP-?-Ch dyads are unique in the sense that they can be used to photogenerate both biradicals and singlet oxygen, thus being able to initiate Ch oxidation from their triplet excited states following either of the two competing mechanistic pathways.

Dataset Information

Methylbismuth: an organometallic bismuthinidene biradical.

Publications

Methylbismuth: an organometallic bismuthinidene biradical.

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