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

## TL;DR

Scientists created a new organometallic ring structure and compared its aromatic properties to organic thiazole rings.

## Contribution

The paper introduces an osmathiazole ring and explores its aromaticity and reactivity in organometallic chemistry.

## Key findings

- The osmathiazole ring is more aromatic than osmaoxazoles but less than organic thiazole.
- Compound 5 undergoes vicarious nucleophilic substitution of hydride with phenylacetylene.
- The osmathiazole ring shows distinct reactivity compared to osmathiazolium cycles.

## Abstract

An osmathiazole skeleton has been generated starting
from the cation
of the salt [OsH(OH)(≡CPh)(IPr)(PiPr3)]OTf (1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene;
OTf = CF3SO3) and thioacetamide; its aromaticity
degree was compared with that of thiazole, and its aromatic reactivity
was confirmed through a reaction with phenylacetylene. Salt 1 reacts with the thioamide to initially afford the synthetic
intermediate [OsH{κ2-N,S-[NHC(CH3)S]}(≡CPh)(IPr)(PiPr3)]OTf (2). Thioamidate and alkylidyne ligands of 2 couple
in acetonitrile at 70 °C, forming a 1:1 mixture of the salts
[OsH{κ2-C,S-[C(Ph)NHC(CH3)S]}(CH3CN)(IPr)(PiPr3)]OTf (3) and [Os{κ2-C,S-[CH(Ph)NHC(CH3)S]}(CH3CN)3(IPr)]OTf (4). Treatment of 3 with potassium tert-butoxide produces the NH-deprotonation of its five-membered ring
and gives OsH{κ2-C,S-[C(Ph)NC(CH3)S]}(IPr)(PiPr3) (5). The
osmathiazole ring of 5 is slightly less aromatic than
the osmathiazolium cycle of 3 and the purely organic
thiazole. However, it is more aromatic than related osmaoxazoles and
osmaoxazoliums. There are significant differences in behavior between 3 and 5 toward phenylacetylene. In acetonitrile,
the cation of 3 loses the phosphine and adds the alkyne
to afford [Os{η3-C3,κ1-S-[CH2C(Ph)C(Ph)NHC(CH3)S]}(CH3CN)2(IPr)]OTf (6), bearing a functionalized allyl ligand. In contrast, the osmathiazole
ring of 5 undergoes a vicarious nucleophilic substitution
of hydride, by acetylide, via the dihydride OsH2(C≡CPh){κ2-C,S-[C(Ph)NC(CH3)S]}(IPr)(PiPr3) (7), which releases H2 to yield Os(C≡CPh){κ2-C,S-[C(Ph)NC(CH3)S]}(IPr)(PiPr3) (8).