Heterogeneous Semiconductors as Versatile Photocatalysts for Organic Synthesis

Visible-light is a powerful “reagent” for sustainable synthetic organic chemistry. In particular, the combination of photo- and nickel catalysis (metallaphotocatalysis) has emerged as a valuable strategy for carbon–carbon and carbon–heteroatom cross-couplings. This research field is dominated by expensive homogeneous noble metal complexes that can only convert a small portion of visible light (<500 nm) into chemical energy. The highenergy photons that excite the photocatalyst can result in unwanted side reactions and the homogenous nature of these does not allow for straightforward catalyst recycling. Heterogeneous semiconductors that absorb visible light are a promising sustainable alternative to noble metal photocatalysts (Chapter 2). Their potential for metallaphotocatalytic C–N cross-couplings was demonstrated (Chapter 3). This transformation suffers from deactivation of the nickel catalyst using homogeneous photocatalysts. The broad absorption range (up to 700 nm) of an organic, heterogeneous carbon nitride photocatalyst (CN‐OA‐m) allows controlling the rate of the bond-forming step by carefully selecting the wavelength thereby preventing catalyst deactivation. This is not only crucial for the reproducibility of such reactions, but also expands the scope to substrates that were previously unsuitable. The redox potential of a carbon nitride photocatalyst can be tuned by changing the irradiation wavelength to generate electron holes with different oxidation potentials (Chapter 4). This was the key to design photo‐chemo‐enzymatic cascades that enable the synthesis of (S)‐ or (R)‐ 1-phenylethan-1-ol from ethylbenzene by choosing the irradiation wavelength and the enzyme co-catalyst. In contrast to common photocatalysts that can be only excited using short wavelengths, abundant organic dyes absorb broadly across the entire visible-light spectrum. Inspired by dye-sensitized solar cells, the short-lived excited singlet states of such dyes were harnessed for light-mediated cross-coupling reactions (Chapter 5). Immobilization of a nickel catalyst on dye-sensitized titanium dioxide results in a material that catalyzes carbon–heteroatom and carbon–carbon bond formations. The modular approach of dye-sensitized metallaphotocatalysts (DSMPs) accesses the entire visible light spectrum and allows tackling selectivity issues resulting from low-wavelengths strategically. The concept overcomes current limitations of metallaphotocatalysis by unlocking the potential of dyes that were previously unsuitable. However, recycling studies suffered from a gradual decrease of the yield due to leaching of the nickel catalyst and the dye from the surface of TiO2. This was rationalized by the weak interaction between carboxylic acid anchoring groups and titanium dioxide. Therefore, recyclable, bifunctional materials for metallaphotocatalytic C–S cross-couplings were developed (Chapter 6). Key to the success was the permanent immobilization through phosphonic acid anchor groups. The optimized catalyst harvests a broad range of the visible light spectrum and requires a nickel loading of only ~0.1 mol%. Another robust alternative to organic dyes that does not suffer from photobleaching was realized, by immobilizing carbon dots on titanium dioxid (Chapter 7). The potential of these sustainable materials was demonstrated for various carbon–heteroatom cross-couplings

Combining artefact analysis, interview and participant observation to study the organizational sensemaking of knowledge-based innovation

"Innovation studies have hardly investigated the link between innovation and organization with respect to what individual actors in organizations mean when they refer to innovation. More precisely, there are few research designs with the goal to understand (Verstehen) the meaning of innovation in organizations. To address this gap on a methodological level, I introduce an interpretative research design to study the organizational sense-making of innovation. Informed by the knowledge-based view of innovation and organizations, this research design suggests a combination of the qualitative methods artefact analysis, semi-structured qualitative interview and participant observation to generate data. Using qualitative content analysis to analyze the collected data separately, first-order concepts are constructed. Joining these separate concepts with the constant comparison technique creates second-order concepts and therefore a comprehensive understanding of the meaning of innovation in an organization. The application of the interpretative research design in innovation studies enables to build new theory on the link between innovation and organization that is empirically grounded." (author's abstract

Emerging concepts in photocatalytic organic synthesis

Visible light photocatalysis has become a powerful tool in organic synthesis that uses photons as traceless, sustainable reagents. Most of the activities in the field focus on the development of new reactions via common photoredox cycles, but recently a number of exciting new concepts and strategies entered less charted territories. We survey approaches that enable the use of longer wavelengths and show that the wavelength and intensity of photons are import parameters that enable tuning of the reactivity of a photocatalysts to control or change the selectivity of chemical reactions. In addition, we discuss recent efforts to substitute strong reductants, such as elemental lithium and sodium, by light, and technological advances in the field

Recyclable, bifunctional metallaphotocatalysts for C–S cross-couplings

Metallaphotocatalytic cross-couplings are typically carried out by combining homogeneous or heterogeneous photocatalysts with a soluble nickel complex. Attempts to realize recyclable catalytic systems use immobilized iridium complexes to harvest light. We present bifunctional, materials for metallaphotocatalytic C–S cross couplings that can be reused without losing their catalytic activity. Key to the success is the permanent immobilization of a nickel complex on the surface of a heterogeneous semiconductor through phosphonic acid anchors. The optimized catalyst harvests a broad range of the visible light spectrum and requires a nickel loading of only ~0.1 mol%

Emerging concepts in photocatalytic organic synthesis

Visible light photocatalysis has become a powerful tool in organic synthesis that uses photons as traceless, sustainable reagents. Most of the activities in the field focus on the development of new reactions via common photoredox cycles, but recently a number of exciting new concepts and strategies entered less charted territories. We survey approaches that enable the use of longer wavelengths and show that the wavelength and intensity of photons are import parameters that enable tuning of the reactivity of a photocatalyst to control or change the selectivity of chemical reactions. In addition, we discuss recent efforts to substitute strong reductants, such as elemental lithium and sodium, by light and technological advances in the field

Today's Children, Tomorrow's America: Six Experts Face the Facts

Compiles essays about trends in family structure; how federal, state, and local budget deficits and projected cuts affect child poverty rates and health; and their long-term implications of reduced investment in children. Includes policy recommendations