Mechanistic Features in Al(I)-Mediated Oxidative Addition of Aryl C–F Bonds: Insights From Density Functional Theory Calculations

Abstract

The oxidative addition of a range of robust aryl C–F bonds to a single Al(I) center supported by a (NacNac)− bidentate ligand ((NacNac)− = [ArNC(Me)CHC(Me)NAr]− and Ar = 2,6–Pr2iC6H3) have been explored by density functional theory calculations. Our calculations demonstrate that the Al(I) center-mediated C–F insertion generally proceeds via the concerted mechanism that involve both the donation (nAl→σC-F*) and back-donation (σF(p)→πAl(p)*) interactions. In addition, the predicted free energy barriers for the C–F bond activation show good agreement with the experimental information available. Finally, the comparative studies show that B(I) is the most active among group III metals (B, Al, Ga), thus supplying a testable prediction for experiments.

Cationic Heterobimetallic Mg(Zn)/Al(Ga) Combinations for Cooperative C–F Bond Cleavage

“… [77] The herein proposed cooperation between the Zn and Al metal centers has been verified by calculating the mechanism for the direct oxidative addition of LAl I to the Ph‐F bond (Figure S59). In agreement with previous calculations,[ 78 , 79 ] the high activation enthalpy of +27.8 kcal mol −1 for this reaction is nearly double that calculated for the conversion: C3 → TS1 → C4 . Note that the C3 → C4 conversion is endothermic (due to loss of aromaticity) and that the C−F bond in C4 (or C5 ) is still intact.…”

Cooperative Bond Activation by a Bimetallic Main-Group Complex

“…Despite the surge of interest in the activation of strong C–F bonds by main-group element compounds, ,, examples involving gallium complexes have, to the best of our knowledge, not been reported, but Li/Ga heterobimetallics have been successfully utilized in C–H bond activation of fluoro­arenes . Furthermore, bond-activation processes by the mononuclear carbene analogs of aluminum and gallium have been actively studied in the past decade, and a recent computational study predicts that the gallanediyl 3 should be able to oxidatively add fluoro­arenes, although associated with higher barriers compared to the aluminum and boron derivatives . Hence, we expected 2 to be reactive toward C–F bonds and monitored its reaction with fluoro­arenes by 1 H NMR spectroscopy.…”

“…17 Furthermore, bond-activation processes by the mononuclear carbene analogs of aluminum and gallium have been actively studied in the past decade, 18 and a recent computational study predicts that the gallanediyl 3 should be able to oxidatively add fluoroarenes, although associated with higher barriers compared to the aluminum and boron derivatives. 19 Hence, we expected 2 to be reactive toward C−F bonds and monitored its reaction with fluoroarenes by 1 H NMR spectroscopy. Quantitative conversion of hexafluorobenzene (a), pentafluorobenzene (b), and 1,2,3,4-tetrafluorobenzene (c) was observed after 1, 2, and 48 h, respectively, Scheme 2.…”

Anti-Electrostatic Main Group Metal–Metal Bonds That Activate CO2

“…Considering the recent interest in bidentate βdiketiminate (BDI) compounds in catalysis, 35 potential to catalyze the oxidative addition of σ bonds such as aryl C−F bonds. 37,38 Since the Al(I) compound acts as a Lewis base, it can easily form a metal−metal bond with a metallic Lewis acid. Indeed, a set of cationic BDI alkaline earth metal (Ae) complexes with main group metal−metal bonds have been synthesized by the Harder group 39,40 and the Crimmin group.…”

“…used a BDI ligand, HC­(CMeNAr) 2 – (Ar = 2,6- i Pr 2 C 6 H 3 ), to synthesize the low valent aluminum compound [{HC­(CMeNAr) 2 }­Al] which is a stable aluminum analogue of a carbene with a lone pair on Al . The Al­(I) center has the potential to catalyze the oxidative addition of σ bonds such as aryl C–F bonds. , Since the Al­(I) compound acts as a Lewis base, it can easily form a metal–metal bond with a metallic Lewis acid. Indeed, a set of cationic BDI alkaline earth metal (Ae) complexes with main group metal–metal bonds have been synthesized by the Harder group , and the Crimmin group .…”