ChemInform Abstract: Novel Ruthenium-Complex-Catalyzed Synthesis of Ureas from Formamides and Amines

Various N,N‘-disubstituted and trisubstituted ureas were obtained in high yields by the ruthenium-complex-catalyzed dehydrogenation of N-substituted formamides and amines under reflux in mesitylene for 12 h under an argon atmosphere. From formanilide (1a) and aniline (2a), N,N ‘-diphenylurea (3a) was obtained in 92% yield. During this reaction, a stoichiometric amount of gaseous hydrogen was spontaneously evolved; thus, the addition of a hydrogen acceptor was not required. Formamide itself, i.e., HCONH2 (4), can also be used as a versatile carbonyl source. From HCONH2 (4) and primary amines, the corresponding N,N‘-disubstituted ureas were obtained in high yields together with the evolution of hydrogen and ammonia. To identify a catalytically active species, the stoichiometric reaction of RuCl2(PPh3)3 with formanilide (1a) was carried out in CH2Cl2 at room temperature to give a novel oxygen-atom-bridged dinuclear ruthenium complex, Ru2(μ-Cl)2Cl2(μ-PhNHCHO-O,O)(PPh3)4 (5), in 87% yield. Complex 5 showed a h...