A novel reaction of the cyano ligand opening an organometallic route to 4-amino imidazoles: four component condensation (4CC) with isocyanide, aldehyde and amine

• Published in: Inorganica Chimica Acta Vol. 222; no. 1; pp. 275 - 290
• Main Authors: Rieger, Dirk, Lotz, Sabine D., Kernbach, Ulrich, Schröder, Sven, André, Christoph, Fehlhammer, Wolf P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1994
• Subjects: Condensation reactions; Crystal structures; Cyano complexes; Imidazoles; Transition metal complexes; Condensation reactions; Crystal structures; Imidazoles; Transition metal complexes; Cyano complexes
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/0020-1693(94)03919-4

Cyano complexes (NEt 4[M(CN)(CO) 5], MCr, Mo, W), isocyanides (CNR 1, R 1Me, Bu t, Cy, Tol P), aldehydes (R 2CHO, R 2=e.g. Ph, Tol P, C 6H 4NMe 2- p, C 6H 4Cl- p) and amine hydrochlorides (R 3NH 3 +Cl −, R 3H, Pr i, Ph, Bz) undergo one-pot, four-component condensation type reactions (4CCs) to give the 4-aminoimidazolin-2-ylidene complexes [M(CO) 5{ CN(H)C(NHR 1)C(R 2)N R 3}] ( 1–24). These include species which have further been functionalized in the 5-position by employing heteroaromatic (2-furanyl, 2-pyrrolyl, 2-thienyl, 2-pyridyl, 2-indenyl) and S-functional (2-thiomethoxyethyl) aldehydes, as well as dinuclear bisheterocycle-bridged ones obtained from dialdehydes (propanedial-1,3) or diamines (e.g. 1,2-diaminoethane, 1,4-diaminobenzene), respectively. Hydrazine in the place of amine gives rise to the carbenoid 1-( N-imino)-4-aminoimidazoles 25–28, products of the incorporation into the heterocycle of in situ formed hydrazones as fourth components. The claimed nature of the complexes 1–28 is confirmed by an X-ray structure analysis of 28 which reveals a largely planar five-membered heterocycle with little delocalization between the MoC1(N1)N2-carbene and C7–C8 π-systems. Mechanistically, the organometallic 4CCs proceed according to their organic analogues which lead to hydantoin-4-imides; with H[Co(CN) 2(dmgH) 2] as acid component, however, a salt-like product was obtained, the X-ray structure analysis of which revealed the presence of an amidinium type cation made up from the carbonyl, isocyanide and two amine components, and of an unchanged complex cyanocobalt counteranion. Detachment of the heterocyles from the complex has been achieved either oxidatively with KMnO 4/Fe(NO 3) 3 to give the 4-amino-5-hydroxo-imidazolin- 2-one 33, or through substitution with pyridine to give the corresponding C2-H imidazole 34.