Origins of Protons in C-H Bond Insertion Products of Phenols: Proton-Self-Sufficient Function via Water Molecules.

Water molecules can serve as proton shuttles for proton transfer in the C-H bond insertion reactions catalyzed by transition metal complexes. Recently, the control experiments performed for C-H bond insertion of phenol and anisol by gold carbenes show that large discrepancy exists in the yields of hydrogenated and deuterated products. Thus, we conducted a detailed theoretical analysis on the function of water molecules in the C-H bond insertion reactions. The comparison of calculated results and control experiments indicates that the solution water molecules play a crucial role of proton shuttle in C-H bond insertion. In particular, it was found that the hydroxyl groups in phenols were capable of donating protons via water shuttles for the production of C-H products, which had a substantial influence on the yields of inserted products. The hydroxyl groups instead of C-H bonds in phenols function like "proton reservoirs" in the C-H bond insertion, which we call the "proton self-sufficient" (PSS) function of phenol. The PSS function of phenol indicates that the substrates with and without proton reservoirs will lead to different C-H bond insertion products.

Reaction mechanisms of carbon dioxide, ethylene oxide and amines catalyzed by ionic liquids BmimBr and BmimOAc: a DFT study.

The mechanisms of the one-pot conversion of carbon dioxide, ethylene oxide, and aniline to 3-phenyl-2-oxazolidionone catalyzed by the binary ionic liquids of BmimBr and BmimOAc were explored using the DFT methods. The complex reaction above comprises of two parallel reactions and a subsequent cascade reaction. DFT calculations on reaction pathways and energy profiles reveal that the electrostatic and hydrogen-bond effects of BmimBr play a crucial role in the parallel reactions for the generation of ethylene carbonate and 2-phenylamino-ethanol. Further, the subsequent cascade reaction to generate 3-phenyl-2-oxazolidinone catalyzed by BmimOAc follows a stepwise mechanism, which is more favorable than the concerted mechanism governed by BmimBr. In addition, BmimBr can accelerate the side reaction of aniline and ethylene oxide to yield a mixture of oligomers, which accords with the experimental observation. This theoretical work provides a deep insight into the catalytic roles of binary ionic liquids and also inspires us to design high efficient catalysts for the conversion of carbon dioxide further.

DFT Calculations on the Mechanism of Transition-Metal-Catalyzed Reaction of Diazo Compounds with Phenols: O-H Insertion versus C-H Insertion.

The reaction of diazo compounds with transition-metal carbenes is an efficient way to achieve the functionalization of chemical bonds in organic molecules, especially for the C-H and O-H bonds. However, the selective mechanisms of C-H and O-H bond insertions by various metal carbenes such as Rh and Cu complexes are not quite clear. In this work, we performed a comprehensively theoretical investigation of the phenol C-H and O-H bonds inserted by Rh and Cu carbenes by using DFT calculations. The calculated results reveal that the nucleophilic additions of phenols to the Rh and Cu carbenes in the C-H bond insertions are the rate-determining steps of whole reactions, which are higher than the barriers in the O-H insertions. In the process of intramolecular [1,3]-H transfer, the Rh and Cu ligands in their carbenes tend to dissociate into solution rather than the intramolecular migration due to their weak metal-carbon bonds. A deeply theoretical analysis of the electronic structures of Rh, Cu, and Au carbenes as well as their complexes elucidated their differences in the chemoselectivity of C-H and O-H insertion products, which agrees with the experimental observations well.

Mechanistic Investigation of Aromatic C(sp(2))-H and Alkyl C(sp(3))-H Bond Insertion by Gold Carbenes.

It was recently reported that the gold-carbenes have an unprecedented catalysis toward the functionalization of C(sp(2))-H bonds of aromatic compounds. However, the associated mechanisms of C(sp(2))-H bonds inserted by gold-carbenes have not been comprehensively understood. We carried out a detailed mechanistic investigation of gold-carbene insertion into the C(sp(2))-H bond of anisole by means of theoretical calculations and control experiments. It significantly reveals that the aromatic C(sp(2))-H bond activation starts with the electrophilic addition of aromatic carbon toward the carbene carbon and subsequently followed the [1,3]-proton shift to form an enol intermediate. The rearrangement of enol proceeds through the mechanisms of proton transfer assisted by water molecules or enol intermediates, which are supported by our control experiments. It was also found that the C(sp(3))-H insertions of alkanes by gold-carbenes proceed through a concerted process via a three-centered transition state. The further comparison of different mechanisms provides a clear theoretical scheme to account for the difference in aromatic C(sp(2))-H and alkyl C(sp(3))-H bond activation, which is instructive for the further experimental functionalization of C-H bonds by gold-carbenes.