•ARTICLES• ...................... ............................... December 2018 Vol.61 No.12: 1594–1599 ............................................................................... https://doi.org/10.1007/s11426-018-9289-9 Metal-free visible-light-mediated aerobic oxidation of silanes to silanols Jing Wang, Bin Li, Li-Chuan Liu, Chenran Jiang, Tao He & Wei He * School of Pharmaceutical Sciences, Tsinghua University, Beijing 100084, China Received May 3, 2018; accepted May 21, 2018; published online August 2, 2018 Oxidation of silanes into silanols using water/air has attracted considerable attention. The known methods with no exception required a metal catalyst. Herein we report the first metal-free method: 2 mol% Rose Bengal as the catalyst, air (O 2 ) as the oxidant, water as the additive and under visible light irradiation. While this method produces various silanols in a simple, cost- effective, efficient (92%–99% yields) and scalable fashion, its reaction mechanism is very different than the reported ones associated with metal catalysis. metal-free, photoredox, aerobic oxidation, silanes Citation: Wang J, Li B, Liu LC, Jiang C, He T, He W. Metal-free visible-light-mediated aerobic oxidation of silanes to silanols. Sci China Chem, 2018, 61: 1594–1599, https://doi.org/10.1007/s11426-018-9289-9 1 Introduction Visible light photoredox catalysis has received rapidly growing attention because it may constitute an ideal platform for sustainable chemistry. It has many conceived advantages due to the characteristics of light (abundant, non-toxic and generating no waste) as well as the related process (oper- ationally simple and scalable) [1]. The past decade has wit- nessed the development of various powerful photoredox catalyst systems [2]. Among them, transition metal dyes [2a– 2d] are extensively studied and most successful. In com- parison, the application of organic dyes [2e–2j] is still limited but warrant further investigations since they are more cost- effective and environmental benign. Silanols are ubiquitous building blocks in silicone industry [3a,3b]. They are also versatile synthons in organic synthesis [3c,3d], serving as nucleophilic partners in cross-coupling reactions [4], organocatalysts for activating carbonyl com- pounds [5] and directing groups for C−H bond activation reactions [6]. In medicinal chemistry, the Si−OH moiety has been ingeniously exploited as enzyme inhibitors [7] and isosteres of pheromones [8]. The classic syntheses of silanols involve hydrolysis of chlorosilanes [9] and less commonly nucleophilic substitution of siloxanes [10]. The direct oxi- dation of hydrosilanes into silanols represents a more de- sirable approach since it produces less byproducts [11]. Conventional methods entail stoichiometric oxidants [11a,11b]. The focus has now shifted to the usage of water and air as the green oxidants [11c–11f]. Our longstanding interest in silicon chemistry has also led to the single-site Au(I) catalyzed water oxidation of silanes [11f]. While these methods provide greener access to silanols, the universal employment of a transition metal catalyst [11g] causes bur- dens in product purification and waste treatment. We thus became curious if it is possible to develop a metal- free aerobic oxidation of slianes using photoredox catalysis. In this context, Fu’s group [12] has reported the first pho- toredox oxidation of silanes with water using a Rh(III) por- phyrins photocatalyst. Herein, we reported the first examples of metal-free visible-light-mediated oxidation of silanes to silanols (Scheme 1). Thus, with low loading (2 mol%) of Rose Bengal [13] as the photocatalyst under white LED ir- © Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature 2018 ..................... chem.scichina.com link.springer.com SCIENCE CHINA Chemistry *Corresponding author (email: whe@tsinghua.edu.cn)