The possibility to utilize electromagnetic irradiation above 400 nm for the initiation of polymerization reactions provides several advantages such as a lower energy demand and higher curing depths in pigmented reactive systems. Recent developments of PIs based on phosphorus and group 14 elements as well as other selected concepts for Type I visible light initiators are outlined and discussed within this review.

In the last decades, there has been an increasing demand for photoinitiators with growing requirements. Nowadays, photoinitiators need to fulfill several properties such as a low-level of toxicity, biocompatibility, fast...

The reduction of 1,1-dibromo-cyclopentasilane with a mildly reducing magnesium­(I) dimer [{(MesNacnac)­Mg−}2] was examined, which gave rise to the formation of endocyclic disilene 1. The formation of 1 was further confirmed by a trapping experiment with MeOH. Additionally, 1 was found to dimerize slowly to 1-dimer. Furthermore, the formation of the homocyclic silylene was demonstrated by performing the reduction in the presence of Et3SiH as a trapping agent. To prevent the 1,2-trimethylsilyl shift, which causes a rapid degradation of the silylene, a second synthetic strategy was established. Therefore, two different tetrasilanes 4 and 5 were synthesized. Compounds 4 and 5 were subsequently reacted with 2.1 equiv of trifluoromethanesulfonic acid to corresponding bis­(trifluoromethanesulfonates) 6 and 7. 1,4-Dihalo-tetrasilanes 8a,b and 9 as well as hexasilanes 10 and 11 were obtained by a subsequent nucleophilic substitution of the triflate substituent with X– (X = Cl–, Br–, or R3Si–). Dianionic species 12 and 13 were synthesized by the reaction of corresponding hexasilanes 10 and 11 with 2.1 equiv of KOt-Bu. Surprisingly, the salt metathesis reaction of dianionic compound 13 does not lead to the formation of the expected 1,1-halocyclopentasilanes. Instead the formation of cyclobutasilane 14 was observed. The reaction of 9 with lithium led again to the formation of 14 alongside with the formation of cyclohexasilane 15. Interestingly, 14 underwent a ring-opening formation by the reaction with gaseous HCl in the presence of AlCl3 and compound 16 was formed. The reduction of 16 allowed straightforward access to 17 as a structurally complex hitherto unknown tricyclic polysilane.

In this contribution we present a novel synthetic procedure towards a variety of bisacyldigermanes via the Corey-Seebach approach. All isolated compounds were characterized by NMR spectroscopy, mass spectrometry and X-ray crystallography. The target compounds were further analyzed via UV/Vis absorption spectroscopy and their longest wavelength absorptions were assigned by DFT calculations. Moreover, we determined the activity of our new photoinitiators by photolysis experiments (photobleaching). Additionally, CIDNP spectra confirmed the radical pathway of the investigated compounds.

In this contribution a convenient synthetic method to obtain the previously unknown dianionic cyclic silenolates and germenolates is described. These dianions 2a , b and 4a , b are easily accessible via a one-pot synthetic protocol in high yields. Their structural properties were analyzed by a combination of NMR, single-crystal X-ray crystallography, and DFT quantum mechanical calculations. Moreover, the reactivity of 2a , b and 4a , b with selected examples of electrophiles was investigated. 2a and 4a were reacted with ClSi i Pr 3 to give new examples of polysilanes and polygermanes with exocyclic double bonds. The reaction of 2b with ClSiMe 2 SiMe 2 Cl led to the formation of the acyl bicyclo[2.2.2]octasilane 6 . Moreover, the reaction of 2a , b and 4a , b with MeI, as an example of a carbon-centered electrophile, led to selective alkylation reactions at the negatively charged silicon and germanium atoms. The corresponding methylated structures 9a , b and 10a , b were formed in nearly quantitative yields. The competitive reactivity of the silyl and silenolate anion toward 1 equiv of ClSiMe 3 showed that the outcome of the reaction was strongly influenced by the substituent at the carbonyl moiety. 2a reacted with 1 equiv of ClSiMe 3 to give the corresponding cyclic silenolate S 1 a , which demonstrated that the silyl anion is more nucleophilic than the silenolate with attached aromatic groups. 2b , on the other hand, reacted with 1 equiv of ClSiMe 3 to give the bicyclic compound 11 via an intramolecular sila-Peterson alkenation reaction. These findings clearly showed that the alkyl-substituted silenolate is more nucleophilic than the silyl anion. This paper demonstrates that 2a , b and 4a , b have the potential to be used as unique building blocks for complex polysilane and polygermane frameworks.