Manganese-Catalyzed Dehydrogenative Synthesis of Urea Derivatives and Polyureas

Abstract

Urea derivatives have significant applications in the synthesis of resin precursors, dyes, agrochemicals, and pharmaceutical drugs. Furthermore, polyureas are useful plastics with applications in coating, adhesive, and biomedical industries. However, the conventional methods for the synthesis of urea derivatives and polyureas involve toxic reagents such as (di)isocyanates, phosgene, CO, and azides. We present here the synthesis of (poly)ureas using much less toxic reagents(di)amines and methanolvia a catalytic dehydrogenative coupling process. The reaction is catalyzed by a pincer complex of an earthabundant metal, manganese, and liberates H 2 gas, valuable by itself, as the only byproduct, making the overall process highly atomeconomic. A broad variety of symmetrical and unsymmetrical urea derivatives and polyureas have been synthesized in moderate to quantitative yields using this catalytic protocol. Mechanistic insights have also been provided using experiments and DFT computation, suggesting that the reaction proceeds via an isocyanate intermediate.

Polyureas as SEI-forming Additives for Li Metal Anodes

“…We have recently discovered a new method for the synthesis of polyureas from the dehydrogenative coupling of diamines and methanol using pincer catalysts of ruthenium 35 or manganese. 36 The polyureas of moderate molecular weight (Mn = 3,000 -11,000) and various functionalities from aromatic, aliphatic, and cyclic diamines can be accessed using this methodology. Interestingly, these polyureas can also be depolymerised back to diamines and methanol via the catalytic hydrogenation process.…”

“…Considering this hypothesis, we synthesized a polyurea/oligourea from the ruthenium/manganese catalysed dehydrogenative coupling of a diamine poly(ethylene glycol) bis(3-aminopropyl) terminated (Mn = 1,500) and methanol as per the method reported by us recently. 35,36 Some of its characteristic details e. g. molecular weight (estimated by 1 H NMR spectroscopy) and physical properties (estimated by TGA and DSC analysis) are listed in Table 1. The use of this polyurea (PU1) as an SEI-forming additive resulted in a slightly higher coulombic efficiency of 10%.…”

“…Although the coulombic efficiency and the number of plating/stripping cycling can be improved, this report demonstrates the first proof of concept that polyureas can potentially be used as a new class of material, for SEI-forming additives in the case of Li-O2 batteries as well as other next-generation batteries with a metal anode. The potentially renewable and recyclable nature of polyureas [35][36][37] present added benefits for the design of a sustainable battery.…”

Manganese Catalysed Dehydrogenative Synthesis of Polyureas from Diformamide and Diamines

“…We have recently expanded the concept of the dehydrogenative synthesis of urea derivatives and reported a new method for the synthesis of polyureas from the dehydrogenative coupling of diamines and methanol using ruthenium [25] and manganese pincer complexes. [26] Liu has also reported the synthesis of polyureas from the dehydrogenative coupling of diamines and methanol using analogous manganese pincer complexes. [27] The discovered method substitutes diisocyanates with methanol which is relatively much less toxic.…”

“…Such transformylation reaction has been reported by us and others in the past. [26] Considering the insoluble nature of the isolated material it is not possible to determine the exact ratio of homopolymer and copolymer. However, for an approximate comparison in different reaction conditions, we have provided the ratio of the integration of aliphatic vs aromatic signals from the 1 H NMR spectra.…”