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Homotropic Cooperativity in Iron-Catalyzed Alkyne Cyclotrimerizations

Geer, Ana M.; Navarro, Janeth; Alamán-Valtierra, Pablo; Coles, Nathan T.; Kays, Deborah L.; Tejel, Cristina

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Ana M. Geer

Janeth Navarro

Pablo Alamán-Valtierra

Nathan T. Coles

Professor of Inorganic Chemistry

Cristina Tejel


Enhancing catalytic activity through synergic effects is a current challenge in homogeneous catalysis. In addition to the well-established metal-metal and metal-ligand cooperation, we showcase here an example of self-activation by the substrate in controlling the catalytic activity of the two-coordinate iron complex [Fe(2,6-Xyl2C6H3)2] (1, Xyl = 2,6-Me2C6H3). This behavior was observed for aryl acetylenes in their regioselective cyclotrimerization to 1,2,4-(aryl)-benzenes. Two kinetically distinct regimes are observed dependent upon the substrate-to-catalyst ratio ([RC≡CH]0/[1]0), referred to as the low ([RC≡CH]0/[1]0 < 40) and high ([RC≡CH]0/[1]0 > 40) regimes. Both showed sigmoidal kinetic response, with positive Hill indices of 1.85 and 3.62, respectively, and nonlinear Lineweaver-Burk replots with an upward curvature, which supports positive substrate cooperativity. Moreover, two alkyne molecules participate in the low regime, whereas up to four are involved in the high regime. The second-order rate dependence on 1 indicates that binuclear complexes are the catalytically competent species in both regimes, with that in the high one being 6 times faster than that involved in the low one. Moreover, Eyring plot analyses revealed two different catalytic cycles, with a rate-determining step more endergonic in the low regime than in the high one, but with a more ordered transition state in the high regime than in the low one.

Journal Article Type Article
Acceptance Date Apr 20, 2023
Online Publication Date Apr 28, 2023
Publication Date Apr 28, 2023
Deposit Date May 9, 2023
Publicly Available Date May 9, 2023
Journal ACS Catalysis
Electronic ISSN 2155-5435
Publisher American Chemical Society (ACS)
Peer Reviewed Peer Reviewed
Volume 13
Pages 6610-6618
Keywords Cooperativity, iron, alkynes, cyclotrimerization, kinetic studies
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