Organolithium‐Initiated Polymerization of Olefins in Deep Eutectic Solvents under Aerobic Conditions

Abstract

Despite their ubiquitous presence in synthesis, the use of polar organolithium reagents under environmentally benign conditions constitutes one of the greatest challenges in sustainable chemistry. Their high reactivity imposes the use of severely restrictive protocols (e.g., moisture‐ and oxygen‐free, toxic organic solvents, inert atmospheres, low temperatures, etc.). Making inroads towards meeting this challenge, a new air‐ and moisture‐compatible organolithium‐mediated methodology for the anionic polymerization of different olefins (e.g., styrenes and vinylpyridines) was established by pioneering the use of deep eutectic solvents (DESs) as an eco‐friendly reaction medium in this type of transformation. Fine‐tuning of the conditions (sonication of the reaction mixture at 40 °C in the absence of protecting atmosphere) along with careful choice of components of the DES [choline chloride (ChCl) and glycerol (Gly) in a 1:2 ratio] furnished the desired organic polymers (homopolymers and random copolymers) in excellent yields (up to 90 %) and low polydispersities (IPD 1.1–1.3). Remarkably, the in situ‐formed polystyril lithium intermediates exhibited a great resistance to hydrolysis in the eutectic mixture 1ChCl/2Gly (up to 1.5 h), hinting at an unexpected high stability of these otherwise highly reactive organolithium species in these unconventional reaction media. This unique stability can be exploited to create well defined block‐copolymers.

DESign of Sustainable One-Pot Chemoenzymatic Organic Transformations in Deep Eutectic Solvents for the Synthesis of 1,2-Disubstituted Aromatic Olefins

“…However, we observed a dramatic decrease in the yield of the reaction (12-21%) when partially soluble (1c-d) or soluble (1e-f) styrenes were employed 5,6 . Similarly, some of us have previously reported an analogous scenario when using organolithium reagents (RLi) in the heterogeneous anionic polymerization of the aforementioned styrenes 1a-d when employing polar eutectic mixtures as reaction media (Sánchez-Condado et al, 2019).…”

“…In this context and during the last decade, a new family of sustainable reaction media, the socalled Deep Eutectic Solvents (DESs) (Abbott et al, 2003(Abbott et al, , 2004 has attracted the attention of many research groups worldwide. As consequence, these neoteric solvents have been broadly applied in chemistry as sustainable reaction media for: (i) polar organometallic chemistry (Mallardo et al, 2014;Vidal et al, 2014Vidal et al, , 2016Sassone et al, 2015;García-Álvarez et al, 2018;Rodríguez-Álvarez et al, 2018;Ghinato et al, 2019); (ii) metal catalyzed organic reactions (García-Álvarez, 2015; Vidal and García-Álvarez, 2019); (iii) biocatalysis (Gotor-Fernández and Paul, 2018); (iv) traditional organic synthesis (Liu et al, 2015;Alonso et al, 2016); (v) metal extraction and electrochemistry (Smith et al, 2014;Millia et al, 2018); and (v) polymer science (Carriazo et al, 2012;del Monte et al, 2014;Mota-Morales et al, 2018;Quirós-Montes et al, 2019;Roda et al, 2019;Sánchez-Condado et al, 2019). These sustainable eutectic solvents can be obtained just by mixing (without any further steps of purification or isolation) two molecules capable of forming a complex intermolecular network based on hydrogenbond interactions.…”

The rise of bio-inspired polymer compartments responding to pathology-related signals

“…To overcome these limitations, controlled ionic polymerizations have been recently performed under ambient conditions in unconventional reaction media, which endow the growing chains with high stability and excellent chain-end fidelity. 84,85 Various non-responsive polymers, such as polystyrene and polydienes or poly[alkyl (meth)acrylates], have been obtained by LIP (Table 2). In addition, styrene derivatives substituted with various functional groups (OH, NH 2 , SH, alkyne, SiOH, aldehyde, keto, and COOH) or other vinyl monomers carrying N atoms (2-or 4-vinyl pyridine) can also undergo successful ionic polymerizations after the appropriate protection of the functional groups.…”

Fast and Chemoselective Addition of Highly Polarized Lithium Phosphides Generated in Deep Eutectic Solvents to Aldehydes and Epoxides

“…[1] However, recently reported synthetic advances in this field have revealed the possibility to promote organic transformations with these reagents using unconventional solvents (e. g., water or bio-based solvents) and bench reaction conditions (air atmosphere and room temperature). [3] Building new bridges between green chemistry [4] and s-block organometallic chemistry, we have recently reported on the successful generation of CÀ C bonds through the direct nucleophilic addition of organolithium (RLi) or organomagnesium (RMgX) reagents to different unsaturated organic electrophiles (e. g., ketones, [5] imines or nitriles, [6] and alkenes [7] ), at room temperature and in the absence of protecting atmosphere, using the so-called deep eutectic solvents (DESs) as sustainable reaction media. [8] These eutectic mixtures can be easily obtained by mixing in a fixed molar ratio hydrogen bond acceptors (HBAs) [e. g., the non-toxic and biorenewable ammonium salt choline chloride (ChCl; 2-hydroxyethyl(trimethyl)ammonium chloride)] with different hydrogen bond donors (HBDs) [e. g., glycerol (Gly), water, urea].…”

“…Bearing this idea in mind and trying to take the aforementioned aerobic organolithium-DESs partnership [5][6][7][8] into a new territory in synthetic organic chemistry, we decided to focus our attention on the organolithium-promoted formation of CÀ P bonds under greener and bench conditions (presence of air and at room temperature). Herein, we first describe the chemoselective and fast addition of lithium phosphides (LiPR 2 ) generated in DES to either aldehydes or epoxides (Scheme 1), under air and at room temperature (bench conditions), using DESs as environmentally responsible reaction media.…”