# Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
## 1 Introduction
### Cross-Metathesis and Related Modifications for Silyalkenyl Fragment Formations
The silylative coupling reaction mediated by the [RuHCl(CO)(PCy\({}_{3}\))\({}_{2}\)]/[CuCl] system was found to be regioselective process leading to both mono- and octa[\((E\))alkenyl]-substituted silsesquioxane T\({}_{8}\) cages (Figure 20) [74; 76], as well as containing metalloids (Ge) [83]. The reactions were conducted with strictly controlled stoichiometry and were clean, as the only byproduct was the evolution of ethylene. These research projects were expanded to a new member of a silsesquioxane family (i.e., a divinyl-substituted double-decker silsesquioxanes which were used as reactants in the silylative coupling and cross-metathesis (only for E = Ge) processes with a wide range of olefins, including highly \(\pi\)-conjugated arenes (Figure 21) [70; 84; 85; 86]. It resulted in the development of a stereoselective method for the preparation of new molecular, dialkenyl-substituted DDSQ derivatives with a well-defined and  
Figure 19: Synthesis of T\({}_{8}\)-based ortho- and metha-carbonaryl-substituted vinylstilbenes. Figure 20: The silylative coupling vs. cross-metathesis leading to octa[\((E\))alkenyl]-substituted silsesquioxane T\({}_{8}\). documented structure ((\(E\)) isomer of -HC=CH-). The applied processes are a complementary tool for the synthesis of this type of systems unique in literature. Interestingly, when dienes were applied, they rendered it possible to exploit the methodology for effective and stereoselective formation of new, macromolecular systems with the DDSQ core embedded in the copolymer chain and the preservation of silylene-ethylene-arylene fragments with double-bond (\(E\)) geometry. This catalytic protocole was the first example in the literature of the synthesis of macromolecular hybrid systems obtained via silylative coupling and cross-metathesis protocols in which the arena unit was stereoselectively connected by the ethenyl bridge with the DDSQ silsesquioxyl fragment. This fragment concerns the silylative (metallicity) coupling process which leads to the highly efficient and stereoselective formation of (\(E\))-alkenylsilyl moieties that are anchored to the silsesquioxane core, irrespective of its structure (cubic or double-decker). It also concerns the amount of Si-HC=CH\({}_{2}\) reactive groups (one, two or eight). Moreover, it may lead to the formation of both molecular and macromolecular silsesquioxane-based compounds. Due to the presence of the (\(E\))-alkenylsilyl units, the resulting functionalized silsesquioxanes are complementary to the architecture of those compounds obtained via cross-metathesis and Heck coupling. Our methodology is an effective, straightforward and clean (only ethylene is a gaseous byproduct) route leading to these systems that are obtained from commercially available reagents. Due to the presence of the (\(E\))-alkenylsilyl fragment and its conjugation with \(\pi\)-arenes, these molecules are potentially of high photophysical interest, as was proved in the case of the analogous POSS-based systems described previously in this review in chapter 3.1 and 3.3. As a result, this kind of \"bottom up\" approach--referring to the synthesis of silsesquioxanes with desired physical and chemical properties--is known, justifiable and used. Hydroisylation of Alkenes and Alkynes as Effcient Procedures for the Introduction of Silylalkanyl and Silylalkenyl Moieties tothe Si-O-Si Core  
In the chemistry of organosilicon compounds, the hydrosilylation process is of key importance and, in this case, it has a predominant role as a fundamental industrial tool for the synthesis of the aforementioned systems [87; 88]. A catalytic insertion of Si-H into multiple bonds, in particular into carbon-carbon unsaturated bonds (C=C and C\(\equiv\)C) including heteroatom, occurs in the presence of transition metal complexes (TM complexes), especially platinum Karstedt's catalyst = [Pt\({}_{2}\)(dvds)\({}_{3}\)], and nickel, rhodium and iridium based systems in homo- and heterogeneous forms, but also with Lewis acids (e.g., AlCl\({}_{3}\)).