3 years ago

Reversible Cleavage/Formation of the Cr-Cr Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization

Yi-Chou Tsai, Gou-Tao Huang, Jen-Shiang Kenny Yu, Yao-Lun Liu, Yu-Siang Huang
Here we report the employment of the quintuply bonded dichromium amidinates [Cr{κ2-HC(N-2,6-iPr2C6H3)(N-2,6-R2C6H3)}]2 (R = iPr (1), Me (7)) as catalysts to mediate the [2+2+2] cyclotrimerization of terminal alkynes giving 1,3,5-trisubstituted benzenes. During the catalysis, the ultrashort Cr-Cr quintuple bond underwent reversible cleavage/formation, corroborated by the characterization of two inverted arene sandwich dichromium complexes (μ-η6:η6-1,3,5-(Me3Si)3C6H3)[Cr{κ2-HC(N-2,6-iPr2C6H3)(N-2,6-R2C6H3)}]2 (R = iPr (5), Me (8)). In the presence of σ donors such as THF and 2,4,6-Me3C6H2CN, the bridging arene 1,3,5-(Me3Si)3C6H3 in 5 and 8 was extruded and 1 and 7 were regenerated. Theoretical calculations were employed to disclose the reaction pathways of these highly regioselective [2+2+2] cylcotrimerization reactions of terminal alkynes.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201709583

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