Abstract
AbstractHerein 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.
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