Research in our group focuses on synthetic inorganic chemistry and material manufacturing, with particular emphasis given to addressing important challenges in the fields of solar energy, catalysis and photochemistry. In addition, through our chemical explorations, we hope to gain fundamental insight into the nature of bonding and reactivity of group 14 compounds. Consequently, researchers in the Haas group will be exposed to a number of advanced synthesis and characterization techniques, including material characterization. The four main research directions are depicted in Chart I.

The classical aldol reaction, particularly its role in the reversible formation and cleavage of carbon-carbon bonds, is one of the most important biosynthetic tools for life on Earth. The versatility and selectivity associated with this process are among the most extensively studied of all synthetic methods. For other group 14 elements, however, such bond-forming reactions were unknown until our group discovered the first aldol reaction of heavier carbon homologues (HCH aldol reaction) identified in cyclic silanes. From a synthetic standpoint, extension of the aldol reaction to acylsilanes, acylgermanes, and acylstannanes initiates a fundamental and direct approach towards carbon-group 14 metal based compounds, and complements standard techniques such as Wurtz reaction, hydrometalation, and transition-metal-catalyzed coupling reactions. Beyond its utility of creating ß-hydroxy acyl subunits, the HCH aldol reaction can selectively deliver complex, unnatural frameworks with high no n-carbon content that are challenging to access via other methods (Scheme 1).

We aspire to explore the HCH aldol reaction, in continuation of our successful work with acylsilanes, as an orthogonal transformation and its applicability on a variety of systems by addressing the following:

• Synthesis of previously unknown group 14 bisacyl compounds as well as unknown group 14 enolates and bisenolates, which serve as precursor molecules for the HCH aldol reaction, including full spectroscopic and structural characterization of the isolated compounds.

• Exploration of intramolecular and intermolecular versions to achieve a comprehensive understanding of the unique and critical steps in the HCH aldol reaction.

• Computational studies to identify and support various inquires of the HCH aldol reaction:

  • Locate potential reaction intermediates and calculate activation energies.

  • Evaluate stereoselectivities.

  • Determine physical properties of isolated products.

• Investigation of isolated group 14 bisacyl compounds with respect to their potential application as high performance photoinitiators.

In the last decades the demand and application of high performance photochemical produced polymers has been immensely growing. Nowadays, their use is no longer restricted to the manufacture of microelectronic devices, coatings, adhesives, inks, printing plates, optical waveguides but also enters fields of medicine (dental filling materials, artificial tissue, heart valves etc.) and fabrication of 3D objects. In the world of photopolymerization, high demands on the performance of the products exist. Moreover, they have to be produced by sustainable, economic and environmentally friendly procedures. To meet the strict qualifications, especially for medical applications, new types of non-toxic photoinitiating systems are necessary. Among the promising PI systems, acylgermanes (Figure 1 compound class 1) can act as suitable radical precursors generating acyl- and germyl-centered radicals upon irradiation, which add very rapidly to double bonds of various monomers. Moreover, they offer the advantages of significantly red-shifted absorption bands and reduced toxicity compared to the frequently applied phosphorus-based (Figure 1 compound class 2a) and campherchinon/amine (Figure 1 compound class 2b) systems. Therefore, germanium-centered PI systems have emerged over the past view years as promising alternatives to the state-of-the-art PI systems. We aspire to investigate new pathways towards acylgermanes, in continuation of our successful work with tetraacylgermanes.

Recently, solution processing of silicon based electronic devices has attracted considerable attention owing to the possibility of low-cost fabrication by printing processes. Moreover, it opens the possibility for large area depositions and patterning materials. Recent studies have demonstrated the principal feasibility of the liquid phase deposition (LPD) and processing of silicon films of satisfactory quality. For future applications LPD processing of silicon based devices must allow continuous manufacturing of all circuit components by successive deposition and printing steps in the same environment. In this context silicon-heteroelement thin layer structures produced by solution routes are of great interest. So far literature contains only scattered reports on LPD processed functional silicon layers. In most of these studies, the use of more than one precursor raised considerable problems. In many cases single-source precursors were shown to be ideal for producing thin films because they provide a simple and clean route to these materials. Open chained and cyclic silicon hydrides such as compounds 1 - 4 (Chart II) are ideal precursors in this context because they are liquid at room temperature, accessible on a preparative scale in high purity, carbon- and oxygen-free, and decompose to elemental silicon upon heating to T > 300 °C.

Therefore, in this project previously unknown heteroelement substituted higher silicon hydrides which contain one or more heteroatoms covalently linked to silicon are synthesized. The resulting materials, then is applied as single source precursors for the deposition of functional silicon films. The project is focused on the elaboration of appropriate pathways suitable for the synthesis of novel heterosubstituted higher silicon hydrides in preparative amounts. After spectroscopic and structural characterization, the resulting materials shall be investigated with respect to thermally and photolytically induced oligomerization processes relevant for the deposition of functional silicon layers. Promising materials, finally, shall be used as single source precursors for LPD processed silicon heterostructures and important film properties such as thickness, homogeneity, elemental composition and morphology shall be investigated.