Theoretical studies on β-aryl elimination from Rh(i) complexes

Abstract

Beta-aryl eliminations in a series of rhodium alkoxide, alkyl and amido complexes were investigated with the aid of density function theory calculations at the Becke3LYP level. Our calculation results indicate that the typical barriers for beta-aryl eliminations are in the range of 20-25 kcal mol(-1). For comparison, beta-allyl and beta-vinyl eliminations were also studied. It was found that beta-allyl elimination is noticeably more favourable than beta-aryl elimination while beta-vinyl elimination is only slightly more favourable. The reversible reactions of beta-aryl elimination correspond to the insertion reactions into a metal-aryl bond. On the basis of the thermochemistry calculated, we discussed the factors influencing the thermodynamic preference of the beta-aryl elimination vs. insertion (the reversible process). The results indicate that the preference can be switched when different substrates and ligands are used.

C–C Activation by Retro-Aldol Reaction of Two β-Hydroxy Carbonyl Compounds: Synergy with Pd-Catalyzed Cross-Coupling To Access Mono-α-arylated Ketones and Esters

“…On the basis of the observations in section and mechanistic proposals for related α-arylation reactions and alcohol C–C activation, ,, a plausible mechanism for this reaction is suggested as shown in Scheme . Oxidative addition of the aryl halide to the Pd(0) active catalyst leads to the formation of intermediate 1 .…”

“…Alcohols are a preferred and versatile class of substrates that are greatly utilized in transition-metal-mediated C–C activation reactions. , A mechanism of β-C elimination has often been invoked for the key C–C bond cleavage of alcohols, which involves a typical four-membered-ring transition state (Scheme a) . Organometallic M–C intermediates are thus generated with the release of a ketone byproduct and undergo further reactions.…”

Metal-Catalyzed Carbon–Carbon Bond Cleavage of Unstrained Alcohols

“…The activation barrier for β-carbon elimination from rhodium alkoxides was calculated by DFT by Lin and coworkers and compared with the corresponding barriers for β-hydride eliminations. 87 According to their calculations, the elimination of a phenyl group requires a much larger barrier (ΔG ⧧ = 23.4 kcal mol −1 ) compared to hydride (ΔG ⧧ = 4.5 kcal mol −1 ).…”

Rhodium-Catalyzed Transarylation of Benzamides: C–C Bond vs C–N Bond Activation

“…On the basis of our work and previous literature, − ,,, DFT calculations were performed to further probe the mechanism of this transformation, and the plausible reaction pathway is shown in Figure . The reaction started from ligand exchange between IM6 and substrate 1a to give catalyst–substrate complex 1a-COM , which directly facilitated the C­(O)–C­(aryl) bond oxidative addition to generate IM1 via 1a-TS-a .…”

“…Meanwhile, the biaryl product ( 1g ) was not detected in this transformation, which illustrated that the C–C bond oxidative addition might occur prior to transmetalation process (Scheme B). , In addition, the fate of the leaving phenyl group of substrate was also investigated. GC-MS analysis of the reaction mixture revealed that benzene ( 1h ) was obtained in 73% yield, which was in 0.88 molar ratio to transarylation product 1c , indicating that β-aryl elimination might be involved in the transmetalation process (Scheme C). According to Hartwig’s work, the H source of benzene would be from the hydroxyl hydrogen of boronic acid, and our deuterium-labeling experiments further confirmed that.…”