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DOI: 10.1055/s-0030-1258741
Rings on Carboranes
Contributor(s):Timothy M. SwagerThe Chinese University of Hong Kong, P. R. of China
Nickel-Catalyzed Regioselective [2+2+2] Cycloaddition of Carboryne with Alkynes
Angew. Chem. Int. Ed. 2010, 49: 4649-4652
Publication History
Publication Date:
21 October 2010 (online)
Key words
cycloaddition - carboranes - acetylenes
Significance
The benzyne equivalent of carborane, carboryne, has been shown previously to form complexes with nickel that undergo stoichiometric [2+2+2] reactions. This catalytic process now allows researchers to make quantities of these interesting materials. The structures produced are electronically interesting delocalized systems that are potential building blocks for electrooptic materials. With unsymmetrical (R¹ = Alk, R² = Ar) acetylenes the products were regiospecific. The authors also make use of a stable in situ generated carboryne precursor.
Comment
The reactions have limited tolerance of functional groups. For example, the reaction failed for Z = O, and gave lower yields in the presence of methyl ethers. Dimethylamine- and ester-containing substrates failed to convert into products. These results are suggestive of catalyst deactivation by substrates and it was also found that excess Ph3P resulted in greatly reduced yields. The authors suggest a step-wise insertion process and a pyridyl-containing substrate revealed a metallocyclic compound consistent with this mechanistic proposal.