Organische Synthesen mit Übergangsmetall‐Komplexen, 63. (β1‐Aminovinyl)carben‐Komplexe und (Alkinyl)aminocarben‐Komplexe von Chrom und Wolfram. — Stereochemie und Isomerisierung

Abstract

Organic Syntheses via Transition Metal Complexes, 63[1]. — (β1‐Aminovinyl)carbene complexes and (Alkinyl)aminocarbene Complexes of Chromium and Tungsten. — Stereochemistry and Isomerization(Alkinyl)alkoxycarbene complexes LnMC(OEt)–CCR 3 [LnMCr(CO)5, W(CO)5; RPh, nBu, SiMe3] react with primary amines H2NR1 4 (R1Me, iPr, allyl, CH2Ph, CHMePh) to give (β1‐aminovinyl)carbene complexes LnMC(OEt)–CHCR‐NHR1 (Z)‐5 (by a Michael‐type 3‐addition) together with (alkinyl)aminocarbene complexes anti‐6 (by a 1‐aminolysis). The product ratio (Z)‐5/anti‐6 is strongly influenced by the reaction temperature: at 20°C (Z)‐5 is obtained as the main product, while at –78°C mainly anti‐6 is formed. Both reactions are stereospecifical; they yield 5 in the (Z), and 6 in the anti configuration only. An anti/syn isomerization is achieved by acidic treatment of anti‐6i. The (alkinyl)aminocarbene complex 6a adds EtOH/EtO– albeit much slower than the (alkinyl)alkoxycarbene complex 3a. A NH21‐Enamino carbene complexes (CO)5CrC(OEt)–CHC(NH2)Ph [(Z)‐8a] is obtained on addition of ammonia to 3a at 90°C.