Ethynylthioamide Complexes : Synthesis, Reactivity and an Unusual Coupling Reaction with Diethylaminopropyne

Abstract

The reaction of [(CO)₅Cr(THF)] with propynethioic acid amides, R–C≡C–C(=S)NMe₂ (R = H, SiMe₃), yields the thioamide complexes [(CO)₅Cr–S=C(NMe₂)C≡C–H] (1a) and [(CO)₅Cr–S=C(NMe₂)C≡C–SiMe₃] (1b). Treatment of solutions of 1a or 1b with methyllithium generates, via deprotonation or desilylation, the lithium salt Li[(CO)₅Cr–S=C(NMe₂)C≡C] (2). On filtration over silica, 2 is readily reprotonated. Complex 1a is inert towards methanol, however, adds diethylamine across the C≡C bond to give the thioacrylamide complex [(CO)₅Cr–=C(NMe₂)C(H)=C(H)NMe₂] (3). Thiourea displaces the thioamide ligand to give [(CO)₅Cr–S=C(NH₂)₂] (4). Complex 1a reacts with half an equivalent of diethylaminopropyne in a three-component coupling to form the homobinuclear complex [(CO)₅Cr–=C(NEt₂)–C(CH₃)=C(H)–C(H)=C(NMe₂)–C≡C–C(NMe2)=S–Cr(CO)₅] (5) in high yield. The solid state structures of complexes 1a and 5 were established by X-ray structural analyses.