Osmathiazole Ring: Extrapolation of an Aromatic Purely Organic System to Organometallic Chemistry.

An osmathiazole skeleton has been generated starting from the cation of the salt [OsH(OH)(≡CPh)(IPr)(PPr)]OTf (; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene; OTf = CFSO) and thioacetamide; its aromaticity degree was compared with that of thiazole, and its aromatic reactivity was confirmed through a reaction with phenylacetylene. Salt reacts with the thioamide to initially afford the synthetic intermediate [OsH{κ--[NHC(CH)S]}(≡CPh)(IPr)(PPr)]OTf (). Thioamidate and alkylidyne ligands of couple in acetonitrile at 70 °C, forming a 1:1 mixture of the salts [OsH{κ--[C(Ph)NHC(CH)S]}(CHCN)(IPr)(PPr)]OTf () and [Os{κ--[CH(Ph)NHC(CH)S]}(CHCN)(IPr)]OTf (). Treatment of with potassium -butoxide produces the NH-deprotonation of its five-membered ring and gives OsH{κ--[C(Ph)NC(CH)S]}(IPr)(PPr) (). The osmathiazole ring of is slightly less aromatic than the osmathiazolium cycle of and the purely organic thiazole. However, it is more aromatic than related osmaoxazoles and osmaoxazoliums. There are significant differences in behavior between and toward phenylacetylene. In acetonitrile, the cation of loses the phosphine and adds the alkyne to afford [Os{η-κ-[CHC(Ph)C(Ph)NHC(CH)S]}(CHCN)(IPr)]OTf (), bearing a functionalized allyl ligand. In contrast, the osmathiazole ring of undergoes a vicarious nucleophilic substitution of hydride, by acetylide, via the dihydride OsH(C≡CPh){κ--[C(Ph)NC(CH)S]}(IPr)(PPr) (), which releases H to yield Os(C≡CPh){κ--[C(Ph)NC(CH)S]}(IPr)(PPr) ().