Towards persistent cyclobutadiene radical cations? The tetra-1-adamantyl-, and tetraneopentylcyclobutadiene radical cations.

✍ Scribed by Q.B. Broxterman; H. Hogeveen; R.F. Kingma

• Publisher: Elsevier Science
• Year: 1984
• Tongue: French
• Weight: 217 KB
• Volume: 25
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)90108-x

✦ Synopsis

The persistence of alkyl substituted cyclobutadiene radical cations strongly depends on the method of generation and the size of the alkyl substituents used. Hindered rotation, the consequence of bulky substituents, is observed in the title compounds. Cyclobutadiene radical cations are transient species amenable to study by ESRlm3 or mass spectroscopy. 4 In order to study these species with other, less sensitive techniques higher concentrations are needed, and thus more persistent examples than those already published are essential. le3 In the present communication results are presented which indicate that the persistence (kinetic stability5) is strongly influenced by two factors: the bulk of the alkyl groups attached to the four-membered ring and the method of generation of the radical cations. We have compared two methods 233 used for the generation of cyclobutadiene radical cations: method A, involving photolysis of a separately prepared d-aluminum halide cyclobutadiene complex,2 and method B, involving photolysis of a mixture of alkyne and Lewis acid3 (Figure 1). Our results show that the radical cation 1 generated by method A is considerably more persistent than that generated by metid B. The decay rates of the tetraethylcyclobutadiene hJ CHZCtZ method A R R #