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

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–S=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–S=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.