A Mechanism Study of Redox Reactions of the Ruthenium-oxo-polypyridyl Complex.

Over the years, RuIV(bpy)2(py)(O)2+([RuIVO]2+) has garnered considerable interest owing to its extensive use as a polypyridine mono-oxygen complex. However, as the active-site Ru=O bond changes during the oxidation process, [RuIVO]2+ can be used to simulate the reactions of various high-priced metallic oxides. In order to elucidate the hydrogen element transfer process between the Ruthenium-oxo-polypyridyl complex and organic hydride donor, the current study reports on the synthesis of [RuIVO]2+, a polypyridine mono-oxygen complex, in addition to 1H and 3H (organic hydride compounds) and 1H derivative: 2. Through 1H-NMR analysis and thermodynamics- and kinetics-based assessments, we collected data on [RuIVO]2+ and two organic hydride donors and their corresponding intermediates and established a thermodynamic platform. It was confirmed that a one-step hydride transfer reaction between [RuIVO]2+ and these organic hydride donors occurs, and here, the advantages and nature of the new mechanism approach are revealed. Accordingly, these findings can considerably contribute to the better application of the compound in theoretical research and organic synthesis.

Pd(II)-Catalyzed Enantioselective Alkynylation of Unbiased Methylene C(sp3)-H Bonds Using 3,3'-Fluorinated-BINOL as a Chiral Ligand.

The first Pd(II)-catalyzed enantioselective alkynylation of unbiased methylene ß-C(sp3)-H bonds is reported. The readily accessible and tunable BINOL derivatives are used as chiral ligands in C-H activation for the first time. 3,3'-Fluorinated-BINOL proved crucial in determining both the reactivity and enantioselectivity. A wide range of carboxylic acid derivatives are well tolerated with high enantioselectivities (up to 96% ee). Mechanistic studies suggest that multiple ligands may participate in the stereodetermining C-H palladation step, and a chiral amplification effect is observed.

Palladium(II)-Catalyzed Enantioselective Arylation of Unbiased Methylene C(sp3 )-H Bonds Enabled by a 2-Pyridinylisopropyl Auxiliary and Chiral Phosphoric Acids.

Enantioselective functionalizations of unbiased methylene C(sp3 )-H bonds of linear systems by metal insertion are intrinsically challenging and remain a largely unsolved problem. Herein, we report a palladium(II)-catalyzed enantioselective arylation of unbiased methylene ß-C(sp3 )-H bonds enabled by the combination of a strongly coordinating bidentate PIP auxiliary with a monodentate chiral phosphoric acid (CPA). The synergistic effect between the PIP auxiliary and the non-C2 -symmetric CPA is crucial for effective stereocontrol. A broad range of aliphatic carboxylic acids and aryl bromides can be used, providing ß-arylated aliphatic carboxylic acid derivatives in high yields (up to 96 %) with good enantioselectivities (up to 95:5 e.r.). Notably, this reaction also represents the first palladium(II)-catalyzed enantioselective C-H activation with less reactive and cost-effective aryl bromides as the arylating reagents. Mechanistic studies suggest that a single CPA is involved in the stereodetermining C-H palladation step.

Nickel-catalyzed direct C-H trifluoroethylation of heteroarenes with trifluoroethyl iodide.

A highly selective nickel-catalyzed C-H trifluoroethylation of heteroarenes was developed with the assistance of a monodentate directing group. This protocol provides efficient access to various trifluoroethyl-substituted heteroarenes, including indoles, pyrroles, furans, and thiophenes, with commercially available CF3CH2I as an alkylation reagent. This robust catalytic procedure is scalable and tolerates a broad range of functional groups. Moreover, multifluoroalkylation of indoles is also viable.

Divergent and Stereoselective Synthesis of ß-Silyl-α-Amino Acids through Palladium-Catalyzed Intermolecular Silylation of Unactivated Primary and Secondary C-H Bonds.

A general and practical PdII -catalyzed intermolecular silylation of primary and secondary C-H bonds of α-amino acids and simple aliphatic acids is reported. This method provides divergent and stereoselective access to a variety of optical pure ß-silyl-α-amino acids, which are useful for genetic technologies and proteomics. It can also be readily performed on a gram scale and the auxiliary can be easily removed with retention of configuration. The synthetic importance of this method is further demonstrated by the late-stage functionalization of biological small molecules, such as (-)-santonin and ß-cholic acid. Moreover, several key palladacycles were successfully isolated and characterized to elucidate the mechanism of this ß-C(sp3 )-H silylation process.

Indole Synthesis via Cobalt(III)-Catalyzed Oxidative Coupling of N-Arylureas and Internal Alkynes.

A mild Co(III)-catalyzed oxidative annulation of N-arylureas and internal alkynes has been developed. The use of less electrophilic ureas other than acetamides as directing groups is crucial for the reaction. A broad range of synthetically useful functional groups are compatible with this reaction, thus providing a new opportunity for the synthesis of diverse indoles.

Copper-/Silver-Mediated Arylation of C(sp(2))-H Bonds with 2-Thiophenecarboxylic Acids.

A copper/silver-mediated arylation of (hetero)aryl C-H bonds with 2-thiophenecarboxylic acids has been achieved. The protocol features a broad substrate scope and high functional group tolerance. Preliminary mechanistic studies indicate that a cascade protodecarboxylation/dehydrogenative coupling process is likely involved.

Ni(II)-catalyzed dehydrative alkynylation of unactivated (hetero)aryl C-H bonds using oxygen: a user-friendly approach.

Ni(II)-catalyzed dehydrative alkynylation of unactivated C(sp(2))-H bonds with terminal alkynes under atmospheric pressure of oxygen was developped. This reaction features the use of catalytic amounts of nickel as the catalyst and O2 as the sole oxidant, providing a user-friendly approach to the synthesis of aryl alkynes.

Ni(II)/BINOL-catalyzed alkenylation of unactivated C(sp(3))-H bonds.

The first nickel-catalyzed alkenylation of unactivated C(sp(3))-H bonds with vinyl iodides is described. The catalytic system comprises an inexpensive and air-stable Ni(acac)2 as the catalyst and BINOL as the ligand, which is highly efficient for the alkenylation of ß-methyl C(sp(3))-H bonds of a broad range of aliphatic carboxamides. The resulting olefins can serve as versatile handles for further preparation. Additionally, we also demonstrated the synthesis of functionalized carboxamides bearing α-quaternary carbon centers from simple pivalamide via nickel-catalyzed sequential C(sp(3))-H bond functionalization.

Nickel-catalyzed direct thiolation of unactivated C(sp(3))-H bonds with disulfides.

The first nickel-catalyzed thiolation of unactivated C(sp(3))-H bonds with disulfides was described. This transformation uses (dppp)NiCl2 as a catalyst and BINOL as a ligand, which are efficient for the thiolation of ß-methyl C(sp(3))-H bonds of a broad range of aliphatic carboxamides. The reaction provides an efficient synthetic pathway to access diverse thioethers.

A sustainable and simple catalytic system for direct alkynylation of C(sp(2))-H bonds with low nickel loadings.

A sustainable and simple catalytic system for the atom-economical alkynylation of benzamides with low nickel loadings is described. No organic or metallic oxidants and expensive ligands are required. A broad range of benzamides and bromoalkynes bearing various synthetically useful functional groups are compatible with this reaction. The versatility of this operationally simple protocol has been further demonstrated by the controllable mono- and di-alkynylation. Importantly, substrate/catalyst ratios of up to 200, and a turnover number of 196 were achieved, highlighting the potential of this protocol for synthetic applications.

Nickel-catalyzed thiolation of unactivated aryl C-H bonds: efficient access to diverse aryl sulfides.

A nickel-catalyzed thiolation of unactivated C(sp(2))-H bonds with disulfides employing the PIP directing group was described. This process uses a catalytic nickel catalyst and no metallic oxidants or cocatalysts are required. The reaction tolerates various important functional groups and heteroarenes, providing an efficient synthetic pathway to access diverse diaryl sulfides.