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Tetraacylgermanes are known as highly efficient photoinitiators. Herein, the synthesis of mixed tetraacylgermanes 4 a–c and 6 a–e with a nonsymmetric substitution pattern is presented. Germenolates are crucial intermediates of these new synthetic protocols. The synthesized compounds show increased solubility compared with symmetrically substituted tetraacylgermanes 1 a–d. Moreover, these mixed derivatives reveal broadened n–π* absorption bands, which enhance their photoactivity. Higher absorption of these new compounds at wavelengths above 450 nm causes efficient photobleaching when using an LED emitting at 470 nm. The quantum yields are in the range of 0.15–0.57, depending on the nature of the aroyl substituents. On the basis of these properties, mixed‐functionalized tetraacylgermanes serve as ideal photoinitiators in various applications, especially in those requiring high penetration depth. The synthesized compounds were characterized by elemental analysis, IR spectroscopy, NMR and CIDNP spectroscopy, UV/Vis spectroscopy, photolysis experiments, and X‐ray crystallography. The CIDNP data suggest that the germyl radicals generated from the new tetraacylgermanes preferentially add to the tail of the monomer butyl acrylate. In the case of 6 a–e only the mesitoyl groups are cleaved off, whereas for 4 a–c both the mesitoyl and the aroyl group are subject to α‐cleavage. [ABSTRACT FROM AUTHOR]

Abstract: The first tetraacylstannanes Sn[(CO)R]4 (R=2,4,6‐trimethylphenyl (1 a) and 2,6‐dimethylphenyl (1 b)), a class of highly efficient Sn‐based photoinitiators, were synthesized. The formation of these derivatives was confirmed by NMR spectroscopy, mass spectrometry, and X‐ray crystallography. The UV/Vis absorption spectra of 1 a, b reveal a significant redshift of the longest wavelength absorption compared to the corresponding germanium compounds. In contrast to the known toxicity of organotin derivatives, the AMES test and cytotoxicity studies reveal intriguing low toxicity. The excellent performance of 1 as photoinitiators is demonstrated by photobleaching (UV/Vis) and NMR/CIDNP investigations, as well as photo‐DSC studies. [ABSTRACT FROM AUTHOR]

Abstract: Acylgermanes provide an outstanding photoinduced reactivity at very useful absorption wavelengths. This encouraged multidisciplinary research groups to utilize them as highly effective and non‐toxic photoinitiators particularly for medical applications. In this Minireview, we present the most recent breakthroughs to synthesize acylgermanes. We also outline mechanistic aspects of photoinduced reactions of several acylgermane derivatives based on fundamental spectroscopic insights. These studies may aid future developments for tailor‐made photoinitiators. [ABSTRACT FROM AUTHOR]

ABSTRACT: Tetrabenzoylgermane 1 and various substituted tetrabenzoylgermanes 2–7 were investigated as visible light (VL) photoinitiators (PIs) for dental dimethacrylate resins and dimethacrylate‐based composites. The tetrabenzoylgermanes 1–7 show a very strong VL absorption between 400 and 450 nm. Substituents on the benzoyl chromophore strongly influence their properties such as melting point, solubility, absorption behavior, or PI reactivity. A good photobleaching behavior and a very high reactivity as VL PI was found in photo‐differential scanning calorimeter experiments for selected tetrabenzoylgermanes. Composite pastes containing only ∼0.1 wt % of Ge‐PI exhibited a sufficient photocuring due to the high PI‐reactivity of the tetraacylgermanes. Among the investigated germane PIs, tetrakis(2‐methylbenzoyl)germane 2 shows the best performance as VL PI for restorative composites and enables the composites to be photocured using an LED with an emission maximum of 500 nm. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46115. [ABSTRACT FROM AUTHOR]

Herein a convenient synthetic method to obtain 2,2,3,3-tetrasilyltetrasilane 3 and 2,2,3,3,4,4-hexasilylpentasilane 4 on a multigram scale is presented. Proton-coupled 29Si NMR spectroscopy and single-crystal X-ray crystallography enabled unequivocal structural assignment. Owing to their unique properties, which are reflected in their nonpyrophoric character on contact with air and their enhanced light absorption above 250 nm, 3 and 4 are valuable precursors for liquid-phase deposition (LPD) and the processing of thin silicon films. Amorphous silicon (a-Si:H) films of excellent quality were deposited starting from 3 and characterized by conductivity measurements, ellipsometry, optical microscopy, and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Acylgermanes have been subject of great interest recently because of their low toxicity and the applicability as sources for germanium-centered radicals for visible-light induced free radical polymerization processes. We report on a novel and versatile method for the synthesis of tetraacylgermanes allowing the preparation of various tetra-substituted acylgermanes 1a-m. The formation of these derivatives was confirmed by NMR spectroscopy, mass spectrometry, and X-ray crystallography. UV-vis absorption spectra of the prepared compounds reveal absorption in the visible region. This transition was assigned by TD-DFT calculations. It enabled a general screening of the influence of different substitution patterns on the absorption properties. The radical formation upon irradiation was confirmed by TR-EPR spectroscopy. [ABSTRACT FROM AUTHOR]

Hier wird ein Syntheseverfahren für Tetraacylgermane Ge[(CO)R]4 (R=Mesityl (1 a), Phenyl (1 b)), eine bis dato unbekannte Verbindungsklasse hochwirksamer germaniumbasierter Photoinitiatoren, beschrieben. Tetraacylgermane sind über eine unkomplizierte Eintopfsynthese in Ausbeuten >85 % zugänglich. Ihre Strukturen konnten mittels NMR ‐ Spektroskopie, Massenspektrometrie und Einkristallstrukturanalyse bestätigt werden. Das Potenzial von 1 a,b als Photoinitiatoren wird durch Photobleaching ‐ (UV ‐ Vis), zeitauflösende EPR ‐ (CIDEP) und NMR/CIDNP ‐ Untersuchungen sowie Photo ‐ DSC ‐ Studien demonstriert. Bemerkenswerterweise übertreffen Tetraacylgermane die Leistungsfähigkeit von derzeit bekannten Photoinitiatoren für die lichtinduzierte radikalische Polymerisation im langwelligen Bereich. Germaniumbasierte Photoinitiatoren für lichtinduzierte radikalische Polymerisationen sind leistungsfähiger als derzeit bekannte Initiatorsysteme, speziell bei Anwendungen im langwelligen Bereich, z. B. für zukünftige Applikationen in der Dentalindustrie. [ABSTRACT FROM AUTHOR]

In this contribution a convenient synthetic method to obtain tetraacylgermanes Ge[C(O)R]4 (R=mesityl ( 1 a), phenyl ( 1 b)), a previously unknown class of highly efficient Ge-based photoinitiators, is described. Tetraacylgermanes are easily accessible via a one-pot synthetic protocol in >85 % yield, as confirmed by NMR spectroscopy, mass spectrometry, and X-ray crystallography. The efficiency of 1 a, b as photoinitiators is demonstrated in photobleaching (UV/Vis), time-resolved EPR (CIDEP), and NMR/CIDNP investigations as well as by photo-DSC studies. Remarkably, the tetraacylgermanes exceed the performance of currently known long-wavelength visible-light photoinitiators for free-radical polymerization [ABSTRACT FROM AUTHOR]

Keywords: acylation; germanes; germanium; photochemistry; photoinitiators EN acylation germanes germanium photochemistry photoinitiators 3190 3190 1 02/17/21 20210215 NES 210215 B Mixed functionalized tetraacylgermanes b were synthesized by two innovative pathways. Acylation, germanes, germanium, photochemistry, photoinitiators Cover Feature: Synthesis of Mixed-Functionalized Tetraacylgermanes (Chem. Eur. J. 10/2021). [Extracted from the article]

Tetraacylgermanes are known as highly efficient photoinitiators. Herein, the synthesis of mixed tetraacylgermanes 4 a-c and 6 a-e with a nonsymmetric substitution pattern is presented. Germenolates are crucial intermediates of these new synthetic protocols. The synthesized compounds show increased solubility compared with symmetrically substituted tetraacylgermanes 1 a-d. Moreover, these mixed derivatives reveal broadened n-π* absorption bands, which enhance their photoactivity. Higher absorption of these new compounds at wavelengths above 450 nm causes efficient photobleaching when using an LED emitting at 470 nm. The quantum yields are in the range of 0.15-0.57, depending on the nature of the aroyl substituents. On the basis of these properties, mixed-functionalized tetraacylgermanes serve as ideal photoinitiators in various applications, especially in those requiring high penetration depth. The synthesized compounds were characterized by elemental analysis, IR spectroscopy, NMR and CIDNP spectroscopy, UV/Vis spectroscopy, photolysis experiments, and X-ray crystallography. The CIDNP data suggest that the germyl radicals generated from the new tetraacylgermanes preferentially add to the tail of the monomer butyl acrylate. In the case of 6 a-e only the mesitoyl groups are cleaved off, whereas for 4 a-c both the mesitoyl and the aroyl group are subject to α-cleavage., (© 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

We introduce a method for the a priori prediction of mass spectra of complex poly(methyl methacrylate)s initiated by photoinitiators featuring multiple cleavage points. The method is based on permutation mathematics using multinomial coefficients to predict the probability of each poly(methyl methacrylate) species' isotopic pattern contribution to the overall mass spectrum. The method assumes a statistical behavior for the cleavage of the photoinitiator. The excellent agreement of the predicted mass spectrum based on multinomial coefficients with the experimental mass spectrum confirms a multipoint cleavage mechanism of the assessed photoinitiators. We exemplify our method for the prediction of mass spectra of poly(methyl methacrylate)s initiated by four tetraacylgermane derivates and one bisacylgermane, recorded after visible light pulsed-laser polymerization by high resolution Orbitrap electrospray ionization mass spectrometry (ESI-MS). The excellent agreement of our approach with experimental data suggests that a wide array of polymer mass spectra of polymers initiated by initiators capable of multiple cleavage events can be quantitatively predicted.