Transition State Energy Decomposition Study of Acetate-Assisted and Internal Electrophilic Substitution C−H Bond Activation by (acac-O,O)₂Ir(X) Complexes (X = CH₃COO, OH)

Abstract

Chelate-assisted and internal electrophilic substitution type transition states were studied using a DFTbased energy decomposition method. Interaction energies for benzene and methane C-H bond activation by (acac-O,O) 2 Ir(X) complexes (X ) CH 3 COO and OH) were evaluated using the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA). A ratio of ∼1.5:1 for forward to reverse charge-transfer between (acac-O,O) 2 Ir(X) and benzene or methane transition state fragments confirms "ambiphilic" bonding, the result of an interplay between the electrophilic iridium center and the internal base component. This analysis also revealed that polarization effects account for a significant amount of transition state stabilization. The energy penalty to deform reactants into their transition state geometry, distortion energy, was also used to understand the large activation energy difference between six-membered and four-membered acetate-assisted transition states and help explain why these complexes do not activate the methane C-H bond.

Overview of the Mechanistic Work on the Concerted Metallation–Deprotonation Pathway

“…When compared computationally, the sixmembered ring transition state using iridium proved to be more easily accessible than the four-membered ring transition state with either a hydroxide ligand or the acetate (Figure 4). 36 Recently, Larrosa and co-workers showed that gold(I) combined with base could metallate arene rings, with primarily results suggesting a CMD mechanism. catalyzed regioselective direct arylation of pyridine N-oxides as well as a variety of diazine and azole N-oxides with arylhalides.…”

Mechanisms of C–H bond activation: rich synergy between computation and experiment

“…84 Hydroxide can only act as an intramolecular base with a 4-membered transition state (see Fig. 14, 21; this process is termed ES by this group) but acetate can have a 4-membered or 6-membered transition state (Fig.…”

The Electronics of CH Activation by Energy Decomposition Analysis: From Transition Metals to Main-Group Metals

“…Our group has also used the ALMO-EDA scheme to analyze methane complexes that are related to Ir, Ru, Os, and Rh metal-ligand complexes that are known to experimentally promote CH bond activation [45]. These metal-ligand complexes differ from CpRe(CO) 2 in that a ligand must be displaced prior to coordination.…”

“…Scheme 7 B3LYP ALMO-EDA energies reported by Ess and coworkers [45]. EDA fragments were defined as (acac) 2 Ir(OAc) and CH 4 …”