摘要
Herein we report the employment of the quintuply bonded dichromium amidinates [Cr{κ 2 -HC(N-2,6- i Pr 2 C 6 H 3 )(N-2,6-R 2 C 6 H 3 )}] 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-η 6 :η 6 -1,3,5-(Me 3 Si) 3 C 6 H 3 )[Cr{κ 2 -HC(N-2,6- i Pr 2 C 6 H 3 )(N-2,6-R 2 C 6 H 3 )}] 2 (R= i Pr (5), Me (8)). In the presence of σ donors, such as THF and 2,4,6-Me 3 C 6 H 2 CN, the bridging arene 1,3,5-(Me 3 Si) 3 C 6 H 3 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.