Abstract
The industrial transition to more-sustainable chemical manufacturing requires the development of a variety of high-performance heterogeneous catalysts. Recently, new classes of heterogeneous and recyclable catalysts that exploit visible-light activation have emerged in the field of organic synthesis. Among these systems, sensitized semiconductors occupy a strategic place as they are able to initiate single electron transfer processes under heterogeneous conditions and using medium-to-low energy light activation. This technology can promote a range of synthetically useful reactions, such as oxidations, reductions, or additions, including C–C bond formation, under very mild conditions and with high selectivity. Sensitized semiconductors have been known for decades in solar cell technologies (the so-called “Dye-Sensitized Solar Cells”) but applications in organic synthesis are only very recent. This Review provides a comprehensive overview of the mechanisms, reactivity, and scope of this technology, with a focus on their new and promising synthetic applications.
Highlights
The development of processes that are less energy-demanding is a crucial endeavor for today’s chemical industry, which has long relied on highly energetic and wasteful approaches
Semiconductors represent a promising class of materials, because they can harvest photons and initiate a charge separation process.[19−22] This technology has been extensively developed over the last 30 years in the field of photovoltaics, but it has only recently started to be applied to organic synthesis.[23]
Except for some examples, such as graphitic carbon nitrides, CdS, and Bi-based nanomaterials,[24−26] the most commonly used semiconductors are only activated by ultraviolet (UV) radiation, which is explained by the relatively high energy required to bridge the gap between the valence band (VB) and the conduction band (CB)
Summary
The development of processes that are less energy-demanding is a crucial endeavor for today’s chemical industry, which has long relied on highly energetic and wasteful approaches. Other triad photocatalytic systems making use of AR/hollow TiO2 Octahedrons/ TEMPO, 1,2-dihydroxyanthraquinone (1,2-DHA)/TiO2/TEMPO, polydopamine/TiO2/TEMPO or Erythrosin B (EB)/Titanate nanotube/TEMPO are reported to perform the oxidation of sulfides to sulfoxides with the same mechanism and similar reduction in reaction times (see Scheme 17).[85,121−123] Kominami et al reported a photocatalytic system composed of 2,3-dihydroxynaphthalene (2,3-DN) and TiO2.135 The catechol group is able to anchor on the titania surface and to induce visible-light sensitization through the formation of a charge-transfer complex.[136] This strategy was used to achieve the selective and almost quantitative reductions of benzaldehydes 2 to their corresponding benzylic alcohols 1. Perspective sensitize TiO2, which allowed the reaction to operate in CH3CN under green or blue light irradiation, yielding the α-substituted aldehydes 104 in moderate yields but with high enantioselectivity (Scheme 39)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
