Mechanism and Origins of Z Selectivity of the Catalytic Hydroalkoxylation of Alkynes via Rhodium Vinylidene Complexes To Produce Enol Ethers

Mechanistic Insight into Palladium/Brønsted Acid Catalyzed Methoxycarbonylation and Hydromethoxylation of Internal Alkene: A Computational Study

Density functional theory (DFT) calculations were performed to study the palladium/Brønsted acid-catalyzed methoxycarbonylation and hydromethoxylation reactions of internal alkene. The calculated results show that the pyridyl group (N atom) in bidentate phosphine ligand with built-in base (L1) plays a crucial role in controlling the selectivity. With the help of the pyridyl group, the methanolysis steps in the methoxycarbonylation reaction and the hydromethoxylation reaction become easy, and both the linear ester methyl 3,4-dimethylpentanoate (P1) and the hydromethoxylation product 2-methoxy-2,3-dimethylbutane (P2) could be obtained. In contrast, the possibility of leading to branched ester P1' was ruled out according to our calculations. The steric effect could account for the observed selectivity. In the presence of the DPEphos ligand (L2) that does not bear the pyridyl group, the methanolysis step in the methoxycarbonylation reaction becomes the rate-determining step with a high overall energy barrier. Neither linear nor branched methoxycarbonylation product could be generated. The palladium/Brønsted acid co-catalyzed hydromethoxylation also become difficult without the assistance of the pyridyl group in the presence of the L2 ligand. Instead, TsOH-catalyzed hydromethoxylation reaction could take place to generate the ether product P2.

Substituent-dependent generation of tricyclic frameworks by the rhodium-catalyzed cycloisomerization of homopropargyl allene-alkynes: a theoretical study

Polycyclic compounds having biological activities can be modified by employing different substituents.

Redox Properties of Mononuclear Dicarbonyl and Carbonylphosphine Rhodium (I) Complexes Containing β-diketonate Ligands

The redox properties of mononuclear dicarbonyl and carbonylphosphine rhodium (I) complexes (CO)(L)Rh(RC(O)CHC(O)R’) with chelate β-diketonate ligands (L = CO, PPh3; R, R’ = Me, Ph; CF3, C4H3S) were studied by electrochemical methods at platinum, glassed carbon and dropping mercury electrodes in acetonitrile. Schemes of their redox reactions were established

Mechanistic Study of Manganese-Catalyzed C-H Bond Functionalizations: Factors Controlling the Competition between Hydroarylation and Cyclization

The Mn-catalyzed C-H functionalization of indoles with allenes developed by Rueping and co-workers provides an efficient access to various alkenylated indoles and substituted pyrroloindolones. Herein, we present a systematic computational study to understand the mechanism and origins of substrate-controlled chemoselectivity of the C-H functionalization reactions (hydroarylation vs cascade cyclization). For the disubstituted allene system, the computed mechanism consists of three main phases: C-H activation, allene migratory insertion, and protonation giving the hydroarylation product. All of these steps are feasible, in agreement with the good yield under the mild experimental conditions. On the other hand, for the trisubstituted allene system, hydroarylation is suppressed due to the higher energy barrier for the protonation step arising from the disfavored ligand-substrate steric repulsions between the carboxide ligand and the substituent group in the allene substrate; our computational results demonstrate that, after the allene insertion leading to a seven-membered cyclometalated intermediate, it undergoes a reaction pathway involving sequential "ketone to enol" isomerization, a 1,4-heteroaryl shift, and β-methoxyl elimination giving the pyrroloindolone product. In contrast, this isomerization → heteroaryl shift → β-methoxyl elimination process is unworkable in the disubstituted allene system, because the protonation step takes place more favorably owing to the lack of ligand-substrate steric interactions. The findings taken together give an insight into the role of the ligand-substrate interactions in directing the competitive pathways and differentiating the energies of key transition states by steric repulsions.

Theoretical investigation of the impact of ligands on the regiodivergent Rh-catalyzed hydrothiolation of allyl amines

The impacts of ligands on regioselectivity were rationalized by using density functional theory calculations.