Synthesis of Fused Metallaaromatics via Intramolecular C–H Activation of Thiophenes

A convenient method to synthesize novel fused ruthena-/osmacycles via intramolecular C–H activation of thiophenes has been developed. Treatment of HC≡CCH(OH)R (R = 2-thienyl) with RuCl2(PPh3)3 or OsCl2(PPh3)3 afforded hydroxyl-coordinated metal vinyl compounds 1 and 4. Reaction of 1/4 with acid produced metal alkenylcarbene complexes 3/5, which can further convert to the corresponding fused metallaaromatics 2/7 via the C(sp2)–H activation of the thienyl groups. 7 is the first example of a metallabenzyne with a fused five-membered ring (thiophene ring). These fused metallaaromatics are thermally stable both in solution and in the solid state in air. The X-ray crystallographic analysis, NMR spectra, and DFT calculations all suggest that these fused metallaaromatics (2 and 7) show aromatic character.