1.2- Dithietes properties

Dithiete, the smallest unsaturated cyclic system with a disulfide bond, has been the subject of interest since 1960 because of its structure, unique bonding properties, and relation to its valence isomer, ethane-1,2-dithione. 

The numerous properties of metallo-dithiolene complexes are a direct consequence of the fantastic redox interplay between the redox-active metal and the dithiolene ligand. A considerable amount of experimental evidence over the last 40 years has pointed to the fact that dithiolenes are highly noninnocent ligands (20, 86, 110, 113, 280-282). That is, they may be viewed in a valence bond description as existing somewhere between the extremes of neutral (dithione/dithiete) and dianionic (dithiolate) forms (Fig. 1). This variable formal... 

Dithiolene synthesis according to (i) was the first entry to the class of tris-dithiolenes King reacted the dithiete (12) with Mo(CO)6 to obtain Mo(tfd)3. The reduction of the julolidinedithione by NaBH4 in THF MeOH, followed by acidification and reaction with aqueous NiClj, led to (9) in excellent yield. As is evident from the MO diagram of dithiolenes (see Section 16.5.3,7) and their established redox properties, method (iii) applies only to dithiolenes with strongly electron-donating substituents, which may stabilize the cationic intermediates. 

As in the case of the corresponding anhydride (23) (Section III.1.C), didehydromaleimide (30) probably does not qualify as a true aryne, but is expected to be sufficiently similar in properties to be covered in this review (Section I.2.C). This species (30) was first suggested as an intermediate along with the 1,2-dithiete (274) in the decomposition of the dithiin (275) in pyridine at 120°C to explain the formation of the aryne trimer (276). When this reaction was carried out in the presence of cyclopentadiene (146b), however, the failure to obtain the appropriate aryne adduct (277) was rationalized as being due to its presumed instability. The only products obtained from this reaction, as well as from butadiene (146c) and anthracene (147), were Diels-Alder adducts such as 278 and 279 of the dithiin (275) and the dithiete (274), respectively. 

---