Isocyanate‐free synthesis of ureas and polyureas via ruthenium catalyzed dehydrogenation of amines and formamides

Abstract

Ethyl formate is very effective for the formylation of amines and diamines to yield formamides and diformamides, respectively. Subsequent dehydrogenation of 1:1 mixtures of formamides and amines or diformamides and diamines with ruthenium pincer catalysts furnishes ureas and polyureas, respectively. This approach provides access to a large structural variety of ureas and polyureas because a wide range of primary amines and diamines are readily converted to the corresponding ureas and polyureas. Small molecule ureas were isolated in yields of up to 95%, whereas polyureas were isolated in lower yields (up to 68%) due to strong adhesion to the reaction flask and poor solubility impeding product removal. Furthermore, the ease with which hydrogen can be removed from the reaction medium enables the synthesis of polyureas with molecular weights that are among the highest reported to date (M n up to 31,100 g mol À1 ). Notably, this synthetic approach does not necessitate high pressure conditions, simplifying equipment needed for their preparation, and it avoids the use of isocyanates, which have significant health concerns.

Manganese-Catalyzed Dehydrogenative Synthesis of Urea Derivatives and Polyureas

“…The concept of the dehydrogenative synthesis of ureas has been recently expanded by us for the synthesis of polyureas from the dehydrogenative coupling of diamines and methanol using the ruthenium-Macho complex D with a TON of up to 100 (Figure ). Along this line, recently, Robertson has reported the synthesis of high-molecular-weight polyureas from the dehydrogenative coupling of diformamides and diamines in the presence of the ruthenium pincer catalyst A . Interestingly, the synthesis of urea derivatives was also demonstrated in one pot starting from ethyl formate and an amine that produced a formamide, which was subsequently reacted with an amine in the presence of the catalyst A to form a urea.…”

“…36 Along this line, recently, Robertson has reported the synthesis of highmolecular-weight polyureas from the dehydrogenative coupling of diformamides and diamines in the presence of the ruthenium pincer catalyst A. 37 Interestingly, the synthesis of urea derivatives was also demonstrated in one pot starting from ethyl formate and an amine that produced a formamide, which was subsequently reacted with an amine in the presence of the catalyst A to form a urea. Replacement of the ruthenium-based catalyst with a catalyst of earth-abundant metal can make the overall process more costeffective and sustainable.…”

Manganese catalysed dehydrogenative synthesis of polyureas from diformamide and diamines

“…3700 Da after day 1; 13 300 Da after day 2; and 32 800 Da after day 3) in a manner expected for a step growth polymerisation mechanism. 25 However, in our case, the formation of insoluble/poorly soluble material at the end of polymerisation reaction has made the estimation of molecular weight difficult. The IR spectrum of the polyurea (entry 1) showed a signal at 1680 cm −1 corresponding to the carbonyl stretching frequency and 1576 cm −1 corresponding to N–H bending both characteristics to a urea functional group.…”

“…1 ). 25 However, the use of precious metals such as ruthenium raises concerns of sustainability due to their high cost and low abundance on the earth's crust. The use of a catalyst based on an earth-abundant metal such as manganese, which is the third most abundant transition metal on earth's crust, can make the process more cost-effective and sustainable.…”

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

“…[24] Guan [25] and Milstein [26] have independently reported the synthesis of polyamides from the dehydrogenative coupling of diols and diamines using a ruthenium-pincer catalyst. We, [27,28] Robertson, [29] and Liu [30] independently reported the synthesis of polyureas from the dehydrogenative coupling of diamines and methanol/diformamides using Macho-type pincer complexes. To the best of our knowledge, the synthesis of branched polyethyleneimine derivatives from alcohols, and amines feedstock has not been reported in peer-reviewed literature.…”