Weiche Gruppe 13/15 organisch-anorganische Hybridmaterialien
Zusammenfassung der Projektergebnisse
Within the scope of this project, novel soft hybrid materials have been developed that combine organic building blocks with inorganic main group elements in their framework. Substitution of selected CC units in organic compounds by their isoelectronic and isosteric BN units has emerged as a viable strategy to produce new materials with structural similarities to their all-carbon congeners but often fundamentally altered electronic features. This “BN/CC isosterism” concept has been very successfully applied to various mono- and polycyclic aromatic hydrocarbons (PAHs), but its application to macromolecular chemistry has only been scarcely studied. With this project, we prepared a series of BN-doped π-conjugated polymers via an unprecedented, highly effective silicon/boron exchange polymerization approach. We presented the first poly(pphenylene iminoborane), which is a BN analogue of the important semiconducting organic polymer poly(p-phenylene vinylene) (PPV). Our studies provided clear-cut evidence for π-electron delocalization across linear B=N linkages along the backbone of a polymer for the first time. Polymers comprising conjugated NBN units in the main chain can be applied as macromolecular poly-ligands, as we demonstrated by crosslinking thereof via zirconium(IV) centers. In view of the importance of inorganic main group polymers such as poly(siloxane)s (silicones), it is surprising that inorganic BN-catenated polymers have been unknown until very recently. Moreover, polymers with a backbone of unsaturated B=N units, i.e., poly(iminoborane)s (PIBs), have been elusive thus far. As the failure of previous attempts to prepare such species was ascribed to the preferred formation of borazines, we developed a concept to effectively suppress this unwanted side reaction through introduction of an ethylene bridge between the N atoms of the monomer. Using this strategy, we succeeded in the synthesis of the first derivatives of this class of compounds, which are inorganic analogues of polyacetylene. In a collaborative effort, we extended this chemistry to BN-containing cyclomatrix polymers networks. These polymers form spherical nanoparticles (microspheres) under precipitation polymerization conditions. In a further collaborative work, we demonstrated the applicability of B-P coupling by Si/B exchange for the synthesis of a P-B-P bridged[3]ferrocenophane. This compound undergoes an intramolecular electron transfer in the mono-oxidized state. A further objective of this project was to develop novel porphyrinoid main group element-doped macrocycles. We succeeded in the synthesis and characterization of the first macrocyclic conjugated tetraboraporphyrinoid. Our studies clearly show that the π-electrons are delocalized over the entire ring system. The green fluorescent compound functions as an effective sensor for fluoride anions. In a third subproject, we succeeded in the development of a new, environmentally benign method for the formation of B-C bonds. It is an unprecedented organocatalytic Si/B exchange condensation process, which we successfully applied to access arylborane molecules, oligomers, and polymers. Some of the products obtained in this way are highly luminescent and can be used as sensory materials for fluoride detection. Previous synthesis routes to such Lewis acidic organoborane polymers and oligomers involved either C-C crosscoupling reactions, which require kinetically particularly stabilized organoborane monomers, or organometallic B-C coupling procedures, the most efficient of which uses highly toxic organotin compounds. As the formation of B-C bonds is fundamental for the construction of organoboron compounds in general, our findings are expected to have significant impact on the broader field of organoboron chemistry.
Projektbezogene Publikationen (Auswahl)
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Mechanisms of the Thermal and Catalytic Redistributions, Oligomerizations, and Polymerizations of Linear Diborazanes, J. Am. Chem. Soc. 2013, 135, 12670–12683
A. P. M. Robertson, E. M. Leitao, T. Jurca, M. F. Haddow, H. Helten, G. C. Lloyd-Jones, I. Manners
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B=N Units as Part of Extended π-Conjugated Oligomers and Polymers, Chem. Eur. J. 2016, 22, 12972–12982
H. Helten
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Dehydrocoupling and Silazane Cleavage Routes to Organic–Inorganic Hybrid Polymers with NBN Units in the Main Chain, Angew. Chem. Int. Ed. 2016, 55, 7236–7241; Angew. Chem. 2016, 128, 7352–7357
T. Lorenz, A. Lik, F. A. Plamper, H. Helten
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Poly(iminoborane)s: An Elusive Class of Main Group Polymers?, Angew. Chem. Int. Ed. 2016, 55, 13321–13325; Angew. Chem. 2016, 128, 13515–13519
O. Ayhan, T. Eckert, F. A. Plamper, H. Helten
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Borazine-based inorganic–organic hybrid cyclomatrix microspheres by silicon/boron exchange precipitation polycondensation, Polym. Chem. 2017, 8, 5264–5268
N. A. Riensch, A. Deniz, S. Kühl, L. Müller, A. Adams, A. Pich, H. Helten
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Catalytic B–C Coupling by Si/B Exchange: A Versatile Route to π-Conjugated Organoborane Molecules, Oligomers, and Polymers, J. Am. Chem. Soc. 2017, 139, 5692–5695
A. Lik, L. Fritze, L. Müller, H. Helten
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Poly(p-phenylene iminoborane): A Boron–Nitrogen Analog of Poly(p-phenylene vinylene), Angew. Chem. Int. Ed. 2017, 56, 2780–2784; Angew. Chem. 2017, 129, 2824–2828
T. Lorenz, M. Crumbach, T. Eckert, A. Lik, H. Helten
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Cyclolinear Oligo- and Poly(iminoborane)s: The Missing Link in Inorganic Main Group Macromolecular Chemistry, Chem. Eur. J. 2018, 24, 5883–5894
O. Ayhan, N. A. Riensch, C. Glasmacher, H. Helten
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Difuryl(supermesityl)borane: a versatile building block for extended π-conjugated materials, Dalton Trans. 2018, 47, 10399–10403 (special issue: New Talent: Europe)
N. A. Riensch, L. Fritze, T. Schindler, M. Kremer, H. Helten
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From Monodisperse Thienyland Furylborane Oligomers to Polymers – Modulating the Optical Properties Through the Hetarene Ratio, Chem. Eur. J. 2018, 24, 11961–11972
A. Lik, S. Jenthra, L. Fritze, L. Müller, K.-N. Truong, H. Helten
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PBP bridged [3]ferrocenophane: a bisphosphanylborane with a redox trigger, Chem. Commun. 2018, 54, 2471–2474
A. Lik, D. Kargin, S. Isenberg, Z. Kelemen, R. Pietschnig,H. Helten
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Catalytic Si/B Exchange Condensation: A Green B–C Coupling Method That Provides Access to Monodisperse (Het)arylborane "Trimers", Synthesis 2019, 51, 399–406
L. Fritze, N. A. Riensch, H. Helten
