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Frühwirt P, Knoechl A, Pillinger M, Müller SM, Wasdin PT, Fischer RC, Radebner J, Torvisco A, Moszner N, Kelterer AM, Griesser T, Gescheidt G, Haas M. The Chemistry of Acylgermanes: Triacylgermenolates Represent Valuable Building Blocks for the Synthesis of a Variety of Germanium-Based Photoinitiators. Inorg Chem 2020; 59:15204-15217. [PMID: 32993291 PMCID: PMC7581296 DOI: 10.1021/acs.inorgchem.0c02181] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
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The formation of
a stable triacylgermenolate 2 as
a decisive intermediate was achieved by using three pathways. The
first two methods involve the reaction of KOtBu or
alternatively potassium with tetraacylgermane 1 yielding 2 via one electron transfer. The mechanism involves the formation
of radical anions (shown by EPR). This reaction is highly efficient
and selective. The third method is a classical salt metathesis reaction
toward 2 in nearly quantitative yield. The formation
of 2 was confirmed by NMR spectroscopy, UV–vis
measurements, and X-ray crystallography. Germenolate 2 serves as a starting point for a wide variety of organo-germanium
compounds. We demonstrate the potential of this intermediate by introducing
new types of Ge-based photoinitiators 4b–4f. The UV–vis absorption spectra of 4b–4f show considerably increased band intensities
due to the presence of eight or more chromophores. Moreover, compounds 4d–4f show absorption tailing up to 525
nm. The performance of these photoinitiators is demonstrated by spectroscopy
(time-resolved EPR, laser flash photolysis (LFP), photobleaching (UV–vis))
and photopolymerization experiments (photo-DSC measurements). Triacylgermenolate 2 was
obtained by using
KOtBu or alternatively potassium. The mechanism involves
the formation of radical anions (shown by EPR). The one-pot synthetic
protocol produces 2 in >95% yield, as confirmed by
NMR
spectroscopy and X-ray crystallography. Germenolate 2 serves as a starting point for a wide variety of organo-germanium
compounds. This was demonstrated by introducing new types of Ge-based
photoinitiators 4b−4f. Their performance
was analyzed by sophisticated spectroscopic methods and photopolymerization
experiments.
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Affiliation(s)
| | | | | | - Stefanie M Müller
- Institute of Chemistry of Polymeric Materials, Montanuniversitaet Leoben, Otto-Gloeckelstrasse 2, A-8700 Leoben, Austria
| | | | | | | | | | - Norbert Moszner
- Ivoclar Vivadent AG, Bendererstraße 2, FL-9494 Schaan, Liechtenstein
| | | | - Thomas Griesser
- Institute of Chemistry of Polymeric Materials, Montanuniversitaet Leoben, Otto-Gloeckelstrasse 2, A-8700 Leoben, Austria
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2
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Nocera G, Young A, Palumbo F, Emery KJ, Coulthard G, McGuire T, Tuttle T, Murphy JA. Electron Transfer Reactions: KO tBu (but not NaO tBu) Photoreduces Benzophenone under Activation by Visible Light. J Am Chem Soc 2018; 140:9751-9757. [PMID: 29996048 DOI: 10.1021/jacs.8b06089] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Long-standing controversial reports of electron transfer from KO tBu to benzophenone have been investigated and resolved. The mismatch in the oxidation potential of KO tBu (+0.10 V vs SCE in DMF) and the first reduction potential of benzophenone (of many values cited in the literature, the least negative value is -1.31 V vs SCE in DMF), preclude direct electron transfer. Experimental and computational results now establish that a complex is formed between the two reagents, with the potassium ion providing the linkage, which markedly shifts the absorption spectrum to provide a tail in the visible light region. Photoactivation at room temperature by irradiation at defined wavelength (365 or 400 nm), or even by winter daylight, leads to the development of the blue color of the potassium salt of benzophenone ketyl, whereas no reaction is observed when the reaction mixture is maintained in darkness. So, no electron transfer occurs in the ground state. However, when photoexcited, electron transfer occurs within a complex formed from benzophenone and KO tBu. TDDFT studies match experimental findings and also define the electronic transition within the complex as n → π*, originating on the butoxide oxygen. Computation and experiment also align in showing that this reaction is selective for KO tBu; no such effect occurs with NaO tBu, providing the first case where such alkali metal ion selectivity is rationalized in detail. Chemical evidence is provided for the photoactivated electron transfer from KO tBu to benzophenone: tert-butoxyl radicals are formed and undergo fragmentation to form (acetone and) methyl radicals, some of which are trapped by benzophenone. Likewise, when KOC(Et)3 is used in place of KO tBu, then ethylation of benzophenone is seen. Further evidence of electron transfer was seen when the reaction was conducted in benzene, in the presence of p-iodotoluene; this triggered BHAS coupling to form 4-methylbiphenyl in 74% yield.
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Affiliation(s)
- Giuseppe Nocera
- Department of Pure and Applied Chemistry , University of Strathclyde , 295 Cathedral Street , Glasgow , G1 1XL , U.K
| | - Allan Young
- Department of Pure and Applied Chemistry , University of Strathclyde , 295 Cathedral Street , Glasgow , G1 1XL , U.K
| | - Fabrizio Palumbo
- Department of Pure and Applied Chemistry , University of Strathclyde , 295 Cathedral Street , Glasgow , G1 1XL , U.K
| | - Katie J Emery
- Department of Pure and Applied Chemistry , University of Strathclyde , 295 Cathedral Street , Glasgow , G1 1XL , U.K
| | - Graeme Coulthard
- Department of Pure and Applied Chemistry , University of Strathclyde , 295 Cathedral Street , Glasgow , G1 1XL , U.K
| | - Thomas McGuire
- Medicinal Chemistry, Oncology, IMED Biotech Unit , AstraZeneca , 319 Milton Road , Cambridge CB4 0WG , U.K
| | - Tell Tuttle
- Department of Pure and Applied Chemistry , University of Strathclyde , 295 Cathedral Street , Glasgow , G1 1XL , U.K
| | - John A Murphy
- Department of Pure and Applied Chemistry , University of Strathclyde , 295 Cathedral Street , Glasgow , G1 1XL , U.K
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Poonpatana P, dos Passos Gomes G, Hurrle T, Chardon K, Bräse S, Masters KS, Alabugin I. Formaldehyde-Extruding Homolytic Aromatic Substitution via C→O Transposition: Selective ‘Traceless-Linker’ access to Congested Biaryl Bonds. Chemistry 2017; 23:9091-9097. [DOI: 10.1002/chem.201700085] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Indexed: 12/26/2022]
Affiliation(s)
- Pabhon Poonpatana
- Discipline of Nanotechnology and Molecular Sciences, Chemistry, Physics and Mechanical Engineering School; Queensland University of Technology (QUT), GPO Box 2434, Brisbane; Queensland 4001 Australia
| | - Gabriel dos Passos Gomes
- Department of Chemistry and Biochemistry; Florida State University; Tallahassee FL 32306-4390 USA
| | - Thomas Hurrle
- Institute of Organic Chemistry (IOC); Karlsruhe Institute of Technology (KIT); Fritz-Haber-Weg 6 76131 Karlsruhe Germany
| | - Kimhoa Chardon
- Discipline of Nanotechnology and Molecular Sciences, Chemistry, Physics and Mechanical Engineering School; Queensland University of Technology (QUT), GPO Box 2434, Brisbane; Queensland 4001 Australia
| | - Stefan Bräse
- Institute of Organic Chemistry (IOC); Karlsruhe Institute of Technology (KIT); Fritz-Haber-Weg 6 76131 Karlsruhe Germany
- Institute of Toxicology & Genetics (ITG); Karlsruhe Institute of Technology (KIT); Kaiserstrasse 12 76131 Karlsruhe Germany
| | - Kye-Simeon Masters
- Discipline of Nanotechnology and Molecular Sciences, Chemistry, Physics and Mechanical Engineering School; Queensland University of Technology (QUT), GPO Box 2434, Brisbane; Queensland 4001 Australia
| | - Igor Alabugin
- Department of Chemistry and Biochemistry; Florida State University; Tallahassee FL 32306-4390 USA
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Barham JP, Coulthard G, Emery KJ, Doni E, Cumine F, Nocera G, John MP, Berlouis LEA, McGuire T, Tuttle T, Murphy JA. KOtBu: A Privileged Reagent for Electron Transfer Reactions? J Am Chem Soc 2016; 138:7402-10. [PMID: 27183183 DOI: 10.1021/jacs.6b03282] [Citation(s) in RCA: 227] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Many recent studies have used KOtBu in organic reactions that involve single electron transfer; in the literature, the electron transfer is proposed to occur either directly from the metal alkoxide or indirectly, following reaction of the alkoxide with a solvent or additive. These reaction classes include coupling reactions of halobenzenes and arenes, reductive cleavages of dithianes, and SRN1 reactions. Direct electron transfer would imply that alkali metal alkoxides are willing partners in these electron transfer reactions, but the literature reports provide little or no experimental evidence for this. This paper examines each of these classes of reaction in turn, and contests the roles proposed for KOtBu; instead, it provides new mechanistic information that in each case supports the in situ formation of organic electron donors. We go on to show that direct electron transfer from KOtBu can however occur in appropriate cases, where the electron acceptor has a reduction potential near the oxidation potential of KOtBu, and the example that we use is CBr4. In this case, computational results support electrochemical data in backing a direct electron transfer reaction.
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Affiliation(s)
- Joshua P Barham
- WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, U.K.,GlaxoSmithKline Medicines Research Centre , Gunnels Wood Road, Stevenage SG1 2NY, U.K
| | - Graeme Coulthard
- WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, U.K
| | - Katie J Emery
- WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, U.K
| | - Eswararao Doni
- WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, U.K
| | - Florimond Cumine
- WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, U.K
| | - Giuseppe Nocera
- WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, U.K
| | - Matthew P John
- GlaxoSmithKline Medicines Research Centre , Gunnels Wood Road, Stevenage SG1 2NY, U.K
| | - Leonard E A Berlouis
- WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, U.K
| | - Thomas McGuire
- AstraZeneca R&D , The Darwin Building, Milton Road, Milton, Cambridge CB4 0FZ, U.K
| | - Tell Tuttle
- WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, U.K
| | - John A Murphy
- WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, U.K
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Meyer AG, Smith JA, Hyland C, Williams CC, Bissember AC, Nicholls TP. Seven-Membered Rings. PROGRESS IN HETEROCYCLIC CHEMISTRY 2016. [DOI: 10.1016/b978-0-08-100755-6.00016-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Lindner S, Bräse S, Masters KS. Simple and expedient metal-free CH-functionalization of fluoro-arenes by the BHAS method – Scope and limitations. J Fluor Chem 2015. [DOI: 10.1016/j.jfluchem.2015.06.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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