A Stable Thiazol‐2‐ylidene and Its Dimer

Abstract

Abstract The synthesis, characterization and X‐ray crystallographic structure determination are described for a stable thiazol‐2‐ylidene 2 . This thiazol‐2‐ylidene is the first example of a stable, crystalline carbene in which the singlet carbene center bears a sulfur substituent. The carbene 2 is the closest stable analog of the important thiamin (vitamin B 1 ) carbene. Although the thiazol‐2‐ylidene 2 is sufficiently stable to isolate at room temperature in the absence of moisture and oxygen, it will dimerize to form a normal carbene–carbene dimer { 2 } 2 . With the isolation and structure determination of both 2 and { 2 2 }, this system is the first in which a stable carbene and its corresponding dimer have been isolated and characterized. Additionally reported is the “reduced” 2 H ‐thiazoline 2 · H 2 in which the former carbene center in 2 has been reduced to a methylene (CH 2 ) group. Thiazol‐2‐ylidenes with smaller groups on nitrogen (e.g. mesityl or methyl) are too unstable to allow easy isolation. The dimer from 3,4,5‐trimethylthiazol‐2‐ylidene possesses a very unusual geometry in which one of the former carbene centers is planar while the second is pyramidal.