Direct synthesis of polyureas from the dehydrogenative coupling of diamines and methanol

Exploiting decarbonylation and dehydrogenation of formamides for the synthesis of ureas, polyureas, and poly(urea-urethanes)

Urea derivatives, polyureas, and poly(urea-urethanes) are materials of great interest. However, their current methods of synthesis involve toxic feedstocks - isocyanate and phosgene gas. There is significant interest in developing alternative methodologies for their synthesis from safer feedstocks. We report here new methods for the synthesis of urea derivatives, polyureas, and poly(urea-urethane) using a ruthenium pincer catalyst. In this approach, urea derivatives and polyureas are synthesized from the self-coupling of formamides and diformamides, respectively, whereas poly(urea-urethanes) are synthesized from the coupling of diformamides and diols. CO and H2 gases are eliminated in all these processes. Decarbonylation of formamides using such organometallic catalysts has not been reported before and therefore mechanistic insights have been provided using experiments and DFT computation to shed light on pathways of these processes.

Direct synthesis of partially ethoxylated branched polyethylenimine from ethanolamine

We report here a method to make a branched and partially ethoxylated polyethyleneimine derivative directly from ethanolamine. The polymerization reaction is catalysed by a pincer complex of Earth-abundant metal, manganese, and produces water as the only byproduct. Industrial processes to produce polyethyleneimines involve the transformation of ethanolamine to a highly toxic chemical, aziridine, by an energy-intensive/waste-generating process followed by the ring-opening polymerization of aziridine. The reported method bypasses the need to produce a highly toxic intermediate and presents advantages over the current state-of-the-art. We propose that the polymerization process follows a hydrogen borrowing pathway that involves (a) dehydrogenation of ethanolamine to form 2-aminoacetaldehyde, (b) dehydrative coupling of 2-aminoacetaldehyde with ethanolamine to form an imine derivative, and (c) subsequent hydrogenation of imine derivative to form alkylated amines.

Catalytic dehydrogenative coupling and reversal of methanol-amines: advances and prospects

The development of efficient hydrogen release and storage processes to provide environmentally friendly hydrogen solutions for mobile energy storage systems (MESS) stands as one of the most challenging tasks in addressing the energy crisis and environmental degradation. The catalytic dehydrogenative coupling of methanol and amines (DCMA) and its reverse are featured by high capacity for hydrogen release and storage, enhanced capability to purify the produced hydrogen, avoidance of carbon emissions and singular product composition, offering the environmentally and operationally benign strategy of overcoming the challenges associated with MESS. Particularly, the cycle between these two processes within the same catalytic system eliminates the need for collecting and transporting spent fuel back to a central facility, significantly facilitating easy recharging. Despite the promising attributes of the above strategy for environmentally friendly hydrogen solutions, challenges persist, primarily due to the high thermodynamic barriers encountered in methanol dehydrogenation and amide hydrogenation. By systematically summarizing various reaction mechanisms and pathways involving Ru-, Mn-, Fe-, and Mo-based catalytic systems in the development of catalytic DCMA and its reverse and the cycling between the two, this review highlights the current research landscape, identifies gaps, and suggests directions for future investigations to overcome these challenges. Additionally, the critical importance of developing efficient catalytic systems that operate under milder conditions, thereby facilitating the practical application of DCMA in MESS, is also underscored.

Synthesis, Structure and Properties of Polyester Polyureas via a Non-Isocyanate Route with Good Combined Properties

Polyureas have been widely applied in many fields, such as coatings, fibers, foams and dielectric materials. Traditionally, polyureas are prepared from isocyanates, which are highly toxic and harmful to humans and the environment. Synthesis of polyureas via non-isocyanate routes is green, environmentally friendly and sustainable. However, the application of non-isocyanate polyureas is quite restrained due to their brittleness as the result of the lack of a soft segment in their molecular blocks. To address this issue, we have prepared polyester polyureas via an isocyanate-free route and introduced polyester-based soft segments to improve their toughness and endow high impact resistance to the polyureas. In this paper, the soft segments of polyureas were synthesized by the esterification and polycondensation of dodecanedioic acid and 1,4-butanediol. Hard segments of polyureas were synthesized by melt polycondensation of urea and 1,10-diaminodecane without a catalyst or high pressure. A series of polyester polyureas were synthesized by the polycondensation of the soft and hard segments. These synthesized polyester-type polyureas exhibit excellent mechanical and thermal properties. Therefore, they have high potential to substitute traditional polyureas.

Synthesis of Polyethyleneimines from the Manganese-Catalysed Coupling of Ethylene Glycol and Ethylenediamine

Polyethyleneimines find many applications in products such as detergents, adhesives, cosmetics, and for processes such as tissue culture, gene therapy, and CO2 capture. The current state-of-the-art technology for the production of the branched polyethyleneimines involves aziridine feedstock which is a highly toxic, volatile and mutagenic chemical and raises significant concern to human health and environment. We report here a novel method for the synthesis of branched polyethyleneimine derivative from ethylene glycol and ethylenediamine which are much safer, environmentally benign, commercially available and potentially renewable feedstock. The polymerisation reaction is catalysed by a complex of an earth-abundant metal, manganese and liberates H2 O as the only by-product. Our mechanistic studies using a combination of DFT computation and experiment suggest that the reaction proceeds by the formation and subsequent hydrogenation of imine intermediates.

Manganese catalysed dehydrogenative synthesis of polyureas from diformamide and diamines

We report here the synthesis of polyureas from the dehydrogenative coupling of diamines and diformamides. The reaction is catalysed by a manganese pincer complex and releases H2 gas as the only by-product making the process atom-economic and sustainable. The reported method is greener in comparison to the current state-of-the-art production routes that involve diisocyanate and phosgene feedstock. We also report here the physical, morphological, and mechanical properties of synthesized polyureas. Based on our mechanistic studies, we suggest that the reaction proceeds via isocyanate intermediates formed by the manganese catalysed dehydrogenation of formamides.

Recent Catalytic Advances on the Sustainable Production of Primary Furanic Amines from the One-Pot Reductive Amination of 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (5-HMF) represents a well-known class of lignocellulosic biomass-derived platform molecules. With the presence of many reactive functional groups in the structure, this versatile building block could be valorized into many value-added products. Among well-established catalytic transformations in biorefinery, the reductive amination is of particular interest to provide valuable N-containing compounds. Specifically, the reductive amination of 5-HMF with ammonia (NH₃ ) and molecular hydrogen (H₂ ) offers a straightforward and sustainable access to primary furanic amines [i. e., 5-hydroxymethyl-2-furfuryl amine (HMFA) and 2,5-bis(aminomethyl)furan (BAMF)], which display far-reaching utilities in pharmaceutical, chemical, and polymer industries. In the presence of heterogeneous catalysts contanining monometals (Ni, Co, Ru, Pd, Pt, and Rh) or bimetals (Ni-Cu and Ni-Mn), this elegant pathway enables a high-yielding and chemoselective production of HMFA/BAMF compared to other synthetic routes. This Review aims to present an up-to-date highlight on the supported metal-catalyzed reductive amination of 5-HMF with elaborate studies on the role of metal, solid support, and reaction parameters. Besides, the recyclability/adaptability of catalysts as well as the reaction mechanism are also provided to give valuable insights into this potential 5-HMF valorization strategy.

Reductive Amination of 5-Hydroxymethylfurfural to 2,5-Bis(aminomethyl)furan over Alumina-Supported Ni-Based Catalytic Systems

Mono- and bimetallic Ni-based catalysts were prepared by screening 6 supports and 14 secondary metals for reductive amination of 5-hydroxymethylfurfural (5-HMF) into 2,5-bis(aminomethyl)furan (BAMF), among which γ-Al₂ O₃ and Mn were the best candidates. By further optimization of the reaction conditions at 0.4 g catalyst loading for 0.5 g substrate of 5-HMF and 160 °C of reaction temperature, 10Ni/γ-Al₂ O₃ and 10NiMn(4 : 1)/γ-Al₂ O₃ achieved the highest BAMF yields of 86.3 and 82.1 %, respectively. Although the BAMF yield values were comparable with that over Raney Ni, the turnover frequencies based on the initial BAMF yield and unit weight of Ni for 10NiMn(4 : 1)/γ-Al₂ O₃ , 10Ni/γ-Al₂ O₃ , and Raney Ni were calculated as 0.41, 0.09, and 0.04 h^-1 , respectively. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy showed that the existence of MnO_x well dispersed on the γ-Al₂ O₃ support and its electron transfer effect with Ni particles on the surface of the support contributed to the high efficiency and better recyclability for the five-time reused 10NiMn(4 : 1)/γ-Al₂ O₃ catalyst.