NOVEL RUTHENIUM-COMPLEX-CATALYZED SYNTHESIS OF UREAS FROM FORMAMIDES AND AMINES

Various N,N'-disubstituted and trisubstituted ureas were obtained in h igh yields by the ruthenium-complex-catalyzed dehydrogenation of N-sub stituted formamides and amines under reflux in mesitylene for 12 h und er an argon atmosphere. From formamide (1a) and aniline (2a), N,N'-dip henylurea (3a) was obtained in 92% yield. During this reaction, a stoi chiometric amount of gaseous hydrogen was spontaneously evolved; thus, the addition of a hydrogen acceptor was not required. Formamide itsel f, i.e., HCONH2 (4), can also be used as a versatile carbonyl source. From HCONH2 (4) and primary amines, the corresponding N,N'-disubstitut ed ureas were obtained in high yields together with the evolution of h ydrogen and ammonia. To identify a catalytically active species, the s toichiometric reaction of RuCl2(PPh3)(3) with formanilide (1a) was car ried out in CH2Cl2 at room temperature to give a novel oxygen-atom-bri dged dinuclear ruthenium complex, Ru-2(mu-Cl)(2)Cl-2(mu-PhNH-CHO-O,O)( PPh3)(4) (5), in 87% yield. Complex 5 showed a high catalytic activity for the synthesis of N,N'-diphenylurea from formanilide (1a) and anil ine (2a), and the stoichiometric reaction of 5 with aniline gave N,N'- diphenylurea, which strongly suggests that complex 5 is the key interm ediate in the RuCl2(PPh3)(3)-catalyzed synthesis of ureas using formam ides as a versatile carbonyl source.