Heterocumulenes, matrix isolation

Carbon monoxide carbo-mers [5-7], i.e., monoxides of linear odd carbon chains longer than one C 0 n = 3, 5, 7, 9...), are highly reactive molecules suggested as potential constituents of interstellar and circumstellar gas clouds. Considerations based on MO theory and quantum chemical calculations indicate that, similar to pure odd carbon chains, all these heterocumulenes are singlet carbenes in the ground state [93]. Since its matrix isolation in 1971 [94] and its synthesis in gas phase in 1983 [95], the simplest member of this family, i.e., tricarbon monoxide C3O, has been extensively studied both experimentally and theoretically [96-102], and its interstellar presence fully confirmed [103]. In particular, on the basis of... 

G. Maier, H. P. Reisenauer, R. Ruppel, Matrix Isolation of Chalcogeno Heterocumulenes, Sulfur Rep. 1999, 21, 335-355. 

The chemical reactivity of the cumulenes under discussion ranges from highly reactive species to almost inert compounds. While some cumulenes can only be generated in a matrix at low temperatures, others are indefinitely stable at room temperature. For example, sulfines and sulfenes are only generated in situ, but some cumulenes with bulky substituents are sometimes isolated at room temperature for example, C=C=S was detected in interstellar space by microwave spectroscopy, and its spectrum was later verified by matrix isolation spectroscopy. In contrast, some cumulenes, such as carbon dioxide and carbon disulfide, are often used as solvents in organic reactions or in the extraction of natural products. The reactivity of some center carbon heterocumulenes in nucleophilic reactions is as follows isocyanates > ketenes > carbodiimides > isothiocyanates. However these reactivities do not relate to the reactivities in cycloaddition reactions. Often reactive cumulenes are isolated as their cyclodimers. Aromatic diisocyanates are more reactive than aliphatic diisocyanates in nucleophilic as well as cycloaddition reactions. 

The carbon monosulfide was generated by a microwave discharge in carbon disulfide. The next higher homolog C3OS 4 was prepared by pyrolysis of the heterocycle 3. Matrix isolation was not necessary, because the heterocumulene is stable under normal conditions, similar to carbon suboxide... 

Oxidation of thioketenes with peracids affords thioketene 5 -oxides (R2C=C=S=0) , a class of heterocumulenes also treated in this chapter. A review of thioketene -oxides was published in 1985. Also, alkylidenethioketenes (R2C=C=C=S) and thiocarbonyl-5 -sulfides (R2C=S=S) are known. The higher homologue, CH2=C=C=C=S, is generated by irradiation of matrix isolated 2,5-diiodothiophene. ... 

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