Synthesis and characterisation of some dimeric η2-diyne compounds of cobalt

Abstract

The organometallic dimers [{Co₂(CO)₆}₂(diyne)] [diyne = C₆H₄(CO₂CH₂C₂H)₂-1,2 1, HC₂CH₂OC₆H₄OCH₂C₂H 2 or HC₂(CH₂)₅C₂H 3] have been synthesized from reactions between [Co₂(CO)₈] and the appropriate diyne ligands. However, the reaction of [Co₂(CO)₈] with diprop-2-ynyl ether HC₂CH₂OCH₂C₂H under similar conditions gave the expected product [{Co₂(CO)₆}₂(µ-HC₂CH₂OCH₂C₂H)] 4 and the unexpected product [Co₄(CO)₁₀(µ-CO){µ₄-η∶η³-CC(CH₂OCH₂)CCH₂}] 5. The products have been characterised by infrared, ¹H NMR spectroscopy and C/H analyses, and 2, 4 and 5 also by single-crystal X-ray crystallography. In 2 and 4 both “yne” fragments of the diyne ligand are bonded to a Co₂(CO)₆ fragment with the CC vector essentially perpendicular to the Co–Co vector. However, in 5 hydrogen migration and new C–C bond formation has led to novel structural features, such as µ₃-CCo₃ and η³-C₃Co units and a “C₄O” ring.