The synthesis of stable triacylgermenolates 3 a,b was achieved by using a multiple silyl abstraction methodology. The formation of these new germenolates was confirmed by NMR spectroscopy and UV‐Vis measurements. Moreover, for the triacylgermenolates 2 and 3 a LIFDI mass spectrometry to characterize these new compounds. Germenolates 3 a,b serve as a starting point for a new triaacylgermane 4 a and two octaacyldigermanes 4 c,d. The formation of these acylgermanes was confirmed by NMR spectroscopy, X‐ray crystallography, UV‐Vis measurements and mass spectrometry. The UV‐Vis absorption spectra of 4 c,d show considerably increased band intensities due to the presence of eight chromophores.
We have synthesized the first isolable geminal bisenolates L2K2Ge[(CO)R]2 (R=2,4,6‐trimethylphenyl (2 a,b), L=THF for (2 a) or [18]‐crown‐6 for (2 b)), a new synthon for the synthesis of organometallic reagents. The formation of these derivatives was confirmed by NMR spectroscopy and X‐ray crystallographic analysis. The UV/Vis spectra of these anions show three distinct bands, which were assigned by DFT calculations. The efficiency of 2 a,b to serve as new building block in macromolecular chemistry is demonstrated by the reactions with two different types of electrophiles (acid chlorides and alkyl halides). In all cases the salt metathesis reaction gave rise to novel Ge‐based photoinitiators in good yields.
The synthetic process to obtain triacylgermenolates with alternated counterions by single-electron-transfer reactions or by a direct approach is described. The formation of these derivatives was confirmed by NMR spectroscopy and UV–vis spectroscopy. Moreover, metal–metal exchange reactions of potassium-substituted triacylgermenolate 2a with MgBr 2 , ZnCl 2 , and HgCl 2 are presented. Additionally, 2a was reacted with n Bu 4 NBr, which led to the formation of ammonia-substituted triacylgermenolate 8 . Furthermore, we reacted 2a with HCl/Et 2 O to obtain triacylgermane 9 . Subsequently, we investigated the reaction of 9 with t Bu 2 Zn and t Bu 2 Hg. NMR spectroscopy, single-crystal X-ray crystallography, and UV–vis spectroscopy are employed for analysis of structural properties.
Since surface-initiated photopolymerization techniques have gained increasing interest within the last decades, the coupling of photoinitiators to surfaces and particles has become an important research topic in material and surface sciences. In terms of surface modification and functionalization, covalently coupled photoinitiators and subsequent photopolymerizations are employed to provide a huge variety of surface properties, such as wettability, stimulus responsive features, antifouling behavior, protein binding, friction control, drug delivery, and many more. For this purpose, numerous type I and type II photoinitiators or other photosensitive moieties have been attached to different substrates so far. In our studies, a convenient and straightforward synthetic protocol to prepare a novel germanium-based photoinitiator (bromotris(2,4,6-trimethylbenzoyl)germane) in good yields was developed. The immobilization of this photoinitiator at the surface of silicon wafers and quartz plates was evidenced by X-ray photoelectron spectroscopy (XPS). Employing visible-light-triggered surface-initiated polymerization of different functional monomers, including acrylamide, perfluorodecyl acrylate, and fluorescein-o-acrylate, surfaces with various features such as hydrophilic/hydrophobic and fluorescent properties were prepared. This was also achieved in a spatially resolved manner. The polymer layers were characterized by contact angle measurements, UV−vis/fluorescence spectroscopy, spectroscopic ellipsometry, and XPS. The thicknesses of the surface grafted polymer layers ranged between 10 and 126 nm.
We report on the synthesis, isolation and unique photoreactivity of a novel symmetric bissilyl-1,2-dione, 3. Its UV/Vis spectrum reveals two remarkable well-separated n→π* absorption bands at λmax = 637 nm (ε = 140 Lmol-1cm-1) and 317 nm (ε = 2460 Lmol-1cm-1). Irradiation at λ = 360/365 nm affords an isolable siloxyketene 4, whereas irradiation at λ = 590-630 nm leads to selective formation of siloxirane 5 by a 1,4-trimethylsilyl migration in high yield. These remarkable wavelength-dependent rearrangements are based on characteristic photochemical reaction pathways. Irradiation at 360/365 nm populates a second excited singlet state (S2) which triggers a hitherto unknown 1,3-hypersilyl migration yielding 4. At longer wavelengths (590/630 nm), the populated first excited singlet state (S1) undergoes intersystem crossing (ISC), and 5 emerges from a triplet (T1) precursor. We have established this reaction mechanism by spectroscopy (optical, in-situ IR, and NMR) and theoretical calculations. NMR and X-ray crystallography reveal the structural features of the products.
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