Application of metal oxide semiconductors in light-driven organic transformations

Abstract

The search for greener alternatives to perform organic reactions has become the order of the day in the chemistry community. In this regard, the use of heterogeneous photocatalysts has emerged as a powerful alternative to replace transition metal-based complexes and organic dyes to enable light-driven organic transformations. Within this realm, metal oxide semiconductors (MOS) have become increasingly popular due to their recyclability, availability, energy efficiency, photo-and chemical stability and generally low toxicity. Here, we cover the most relevant literature related to the use of MOS as photocatalysts to light induce organic reactions, including oxidations, C-C and C-heteroatom bond formations. We also discuss the mechanisms involved in these processes, as well as the hitherto best known MOS modifications able to enhance their photocatalytic performance.

Photoredox Organic Synthesis Employing Heterogeneous Photocatalysts with Emphasis on Halide Perovskite

“…Overview of typical reactionsc atalyzedbyb and structure modified visible light sensitive metal oxides under visible light. [65][66][67][68][69]72] ous optimization of the QDs or the reaction conditions. The successo ft hese complicatedo rganic transformations, particularly many of whicha re key for important pharmaceutical scaffolds, demonstrates that photoredox catalysis using heterogeneous colloidal nanocrystals has become an imperative route in functionalg roup tolerant,h igh yield, complicated organic synthesis.…”

“…To date, several approaches have been developed: 1) introduction of transition metals as dopants into the metal oxide lattice; 2) introduction of defects into metal oxides; 3) modification of the surface of metal oxides with dye compounds . Benefiting from these strategies, metal oxide semiconductors have been successfully exploited in several types of transformations, as shown in Figure , including but not limited to 1) the oxidation of alcohols to carbonyl compounds, amines to imines or nitrosobenzenes, alkenes to epoxides, and alkanes to aldehydes or ketones; 2) the reduction of nitrobenzenes to aminobenzenes or azo benzenes under O 2 ‐free conditions; 3) C−H bond activation and functionalization via nucleophilic attack to construct new C−C or C−X (X=O, N, or S) bonds; 4) the cross‐coupling of organohalides with other compounds to form new C−C bonds . Overall, metal oxide photocatalysts currently still suffer from low charge carrier separation efficiency, poor carrier mobility, and undesirable photoresponse in the visible range.…”

Heterogeneous photocatalysis in flow chemical reactors

“…This review aims to be of interest to synthetic organic chemists who are considering applying heterogeneous photocatalysis (HPC) and flow chemistry in their research, and especially those who are already involved in one of the two areas. Many independent reviews have focused on individual types of HPCat materials [1][2][3][4][5][6][7], and their applications in organic synthesis [8][9][10][11], solar fuel production [12][13][14][15][16][17], and environmental remediation [18][19][20][21][22][23]. Herein, we review the recent applications of HPCats in flow reactors for organic synthesis, as to the best of our knowledge, there is no review dedicated to this important and developing research area.…”

Pushing the boundaries of C–H bond functionalization chemistry using flow technology

“…For this reason, TiO 2 is frequently used for the oxidative solar decontamination of waste water [192]. As an abundant, non-toxic and heterogeneous photocatalyst, it is a very attractive material for sustainable chemistry [193], the downside being the band gap of unmodified TiO 2 is too large for the creation of electrons and holes through visible light irradiation. This problem is generally solved through the use of modified TiO 2 [194], e.g.…”