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

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 (Mn up to 31,100 g mol−1). 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. The table of contents entry: Ethyl formate effectively formylates amines and diamines. Ruthenium pincer complexes dehydrogenatively couple the resulting formamides and diformamides with amines and diamines to produce ureas and polyureas, respectively (with Mn values up to 31,100 g mol−1) in good yields.