Synthesis and co-ordination chemistry of dicobalt-complexed thiacycloalkynes

The reactions of bis(2-mercaptoethyl) sulfide or bis(2-mercaptoethyl) ether with [Co₂(μ-HOCH₂C≡CCH₂OH)(CO) ₆] in the presence of HBF₄·OEt₂ afford [Co₂{μ-C₂(CH₂SCH₂CH ₂)₂X}(CO)₆] (X = S or O) respectively together with dimeric products. The structure of the monomer [Co₂{μ-C ₂(CH₂SCH₂CH₂)₂S}-(CO) ₆] has been established by X-ray crystallography and comprises a hexacarbonyldicobalt unit transversely bridged via the alkyne functionality of 1,4,7-trithiacycloundec-9-yne which has an exodentate conformation. Proton NMR studies of the bis(2-mercaptoethyl) sulfide derivatives reveal that the SCH ₂CH₂S linkages are predominantly anti in solution. The monomers undergo carbonyl substitution by bis(diphenylphosphino)methane (dppm) to afford [Co₂{μ-C₂(CH₂SCH ₂CH₂)₂X}(μ-dppm)(CO)₄] (X = S or O) which react with [Mo(CO)₃(η-C₆H₃Me ₃-1,3,5)] to afford products in which the macrocycles face cap Mo(CO)₃ fragments. Reaction of [Co₂{μ-C ₂(CH₂SCH₂CH₂)₂S}(CO) ₆] with AgBF₄ and PPh₃ yields [Co ₂{μ-C₂(CH₂SCH₂CH ₂)₂S}(CO)₆{Ag(PPh₃)}]BF₄ for which an X-ray crystallographic study revealed that the Ag(PPh ₃)⁺ fragment is co-ordinated by all three sulfur atoms of the ring which adopts an endodentate conformation. Reaction of [Co ₂{μ-C₂(CH₂SCH₂CH ₂)₂S}(CO)₆] with [Cu(MeCN)₄]PF ₆ affords [Co₂{μ-C₂(CH₂SCH ₂CH₂)₂S}(CO)₆{Cu(MeCN)}]PF ₆ containing a labile acetonitrile ligand which undergoes substitution by phosphines. The dimeric compound [(CO)₆Co ₂{μ-(CCH₂SCH₂-CH₂SCH ₂CH₂SCH₂C)₂}Co₂(CO) ₆] produces a 1:1 adduct when treated with AgBF₄. X-Ray crystallography reveals that the silver ion is co-ordinated by four of the six available thioether groups.