A Stable Thiazol‐2‐ylidene and Its Dimer

Abstract

AbstractThe 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 B1) 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 {22}, this system is the first in which a stable carbene and its corresponding dimer have been isolated and characterized. Additionally reported is the “reduced” 2H‐thiazoline 2 · H2 in which the former carbene center in 2 has been reduced to a methylene (CH2) 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.