A Well‐Defined Aluminum‐Based Lewis Acid as an Effective Catalyst for Diels–Alder Transformations

Abstract

A catalytically active aluminum-based system for Diels-Alder transformations is reported. The system was generated by mixing a β-diketiminate-stabilized aluminum bistriflate compound with Na[BAr(Cl) 4 (Ar(Cl) =3,5-Cl2 C6 H3). Solid-state analysis of the catalytic system reveals a unique structure incorporating a two-dimensional coordination polymer. According to the experimental results obtained from several Diels-Alder transformations, the aluminum-based system appears to be a more practical and more robust alternative to the recently reported compounds based on carbon and silicon cations.

Rationalizing the Activity of an “Artificial Diels-Alderase”: Establishing Efficient and Accurate Protocols for Calculating Supramolecular Catalysis

“…To rationalize these differences, we explored the electronic and steric contributions to the reaction energy in each system. In both cases, and as previously seen for Lewis acid-catalyzed [4+2] cycloadditions, [67][68][69] the cages enhance the electrophilic character of the dienophile bound in the cavity. Polarization of the dienophile within the cage leads to a net charge of +0.25 and +0.16 in bq for C-1 and C-2, respectively, 70 leading to a lowering the LUMO energy by 1.5 and 1.6 eV in C-1 and C-2, respectively (Table S19).…”

Rationalizing the “Diels-Alderase” Activity of Pd2L4 Self-Assembled Metallocages: Enabling the Efficient Prediction of Catalytic Scaffolds

“…To rationalize these differences, we explored the electronic and steric aspect of each system. In both cases, and as previously seen for Lewis acid-catalyzed [4+2] cycloadditions, [71][72][73] the cages enhance the electrophilic character of the dienophile bound in the cavity. Polarization of the dienophile within the cage leads to a net charge of +0.25 and +0.16 in bq for C-1 and C-2, respectively ( Figure S14), 74 leading to a lowering the LUMO energy by 1.6 / 1.5 eV in C-1 and C-2, respectively.…”

N‐Heterocyclic Carbene Complexes of Cp*–Aluminum Triflate

“…1.798 Å) and 3b (avg. 1.805 Å) are longer than the 1.767 Å observed in (Ar‐nacnac)AlOTf 2 (Ar = 2,6‐ i Pr 2 –C 6 H 3 ), implying the dissociation of triflate may take place in solution.…”

“…In an attempt to introduce triflates into the compounds, the initial approach was to follow the synthetic protocol developed for (Ar‐nacnac)AlOTf 2 (Ar = C 6 F 5 , 2,6‐ i Pr 2 –C 6 H 3 ), in which the halide substituent at Al was substituted by triflate via addition of AgOTf into the CH 3 CN solution of (Ar‐nacnac)AlCl 2 at room temperature. [11a], The η 1 ‐Cp*AlCl 2 (SIMes) ( 1 ) obtained from coordination of SIMes to [η 5 ‐Cp*AlCl 2 ] 2 (Scheme ) features a 27 Al NMR resonance at δ = 104 ppm, which is considerably downfield shifted compared to that of [Cp*AlCl 2 ] 2 ( δ = –51 ppm). The observed chemical shift is in accordance with the change in hapticity of Cp* from η 5 to η 1 yielding a tetra‐coordinated Al center.…”