Dual electronic effects achieving a high-performance Ni(II) pincer catalyst for CO2 photoreduction in a noble-metal-free system.

A carbazolide-bis(NHC) NiII catalyst (1; NHC, N-heterocyclic carbene) for selective CO2 photoreduction was designed herein by a one-stone-two-birds strategy. The extended π-conjugation and the strong σ/π electron-donation characteristics (two birds) of the carbazolide fragment (one stone) lead to significantly enhanced activity for photoreduction of CO2 to CO. The turnover number (TON) and turnover frequency (TOF) of 1 were ninefold and eightfold higher than those of the reported pyridinol-bis(NHC) NiII complex at the same catalyst concentration using an identical Ir photosensitizer, respectively, with a selectivity of ∼100%. More importantly, an organic dye was applied to displace the Ir photosensitizer to develop a noble-metal-free photocatalytic system, which maintained excellent performance and obtained an outstanding quantum yield of 11.2%. Detailed investigations combining experimental and computational studies revealed the catalytic mechanism, which highlights the potential of the one-stone-two-birds effect.

Formation of Stable NiIII N-Confused Porphyrins Aided by a 3-Ethoxy Group.

We report the synthesis, characterization, and reactivities of two stable NiIII N-confused porphyrin (NCP) complexes. Metalation of 3-OEt NCP 1 with NiCl2 ⋅ 6H2 O in CHCl3 /EtOH gave 3-OEt NiII NCP 3 initially, which was easily oxidized in air to form the NiIII complex of NCP inner C-oxide 4. Bis-ethoxy-modified NiIII complex 5 was synthesized by oxidation of 3 with PIFA in ethanol and CHCl3 . The structures of 4 and 5 were determined by single-crystal X-ray diffraction analysis. An unusually long NiIII -C bond (2.170(9) Å) was observed in 4. The g-factor (g>2.1) observed in the EPR spectra of 4 and 5 further confirmed that they are paramagnetic NiIII complexes. Comparative experiments showed that the 3-ethoxy group plays an important role in the formation of 4 and 5. Reduction of 4 and 5 with NaBH4 regenerated complex 3.

Tungsten-Catalyzed Direct N-Alkylation of Anilines with Alcohols.

The implementation of non-noble metals mediated chemistry is a major goal in homogeneous catalysis. Borrowing hydrogen/hydrogen autotransfer (BH/HA) reaction, as a straightforward and sustainable synthetic method, has attracted considerable attention in the development of non-noble metal catalysts. Herein, we report a tungsten-catalyzed N-alkylation reaction of anilines with primary alcohols via BH/HA. This phosphine-free W(phen)(CO)4 (phen=1,10-phenthroline) system was demonstrated as a practical and easily accessible in-situ catalysis for a broad range of amines and alcohols (up to 49 examples, including 16 previously undisclosed products). Notably, this tungsten system can tolerate numerous functional groups, especially the challenging substrates with sterically hindered substituents, or heteroatoms. Mechanistic insights based on experimental and computational studies are also provided.

Sustainable and Selective Alkylation of Deactivated Secondary Alcohols to Ketones by Non-bifunctional Pincer N-heterocyclic Carbene Manganese.

A sustainable and green route to access diverse functionalized ketones via dehydrogenative-dehydrative cross-coupling of primary and secondary alcohols is demonstrated. This borrowing hydrogen approach employing a pincer N-heterocyclic carbene Mn complex displays high activity and selectivity. A variety of primary and secondary alcohols are well tolerant and result in satisfactory isolated yields. Mechanistic studies suggest that this reaction proceeds via a direct outer-sphere mechanism and the dehydrogenation of the secondary alcohol substrates plays a vital role in the rate-limiting step.

Nonbifunctional Outer-Sphere Strategy Achieved Highly Active α-Alkylation of Ketones with Alcohols by N-Heterocyclic Carbene Manganese (NHC-Mn).

The unusual nonbifunctional outer-sphere strategy was successfully utilized in developing an easily accessible N-heterocyclic carbene manganese (NHC-Mn) system for highly active α-alkylation of ketones with alcohols. This system was efficient for a wide range of ketones and alcohols under mild reaction conditions, and also for the green synthesis of quinoline derivatives. The direct outer-sphere mechanism and the high activity of the present system demonstrate the potential of nonbifunctional outer-sphere strategy in catalyst design for acceptorless dehydrogenative transformations.

Stereoselective synthesis of sulfur-containing ß-enaminonitrile derivatives through electrochemical Csp3-H bond oxidative functionalization of acetonitrile.

Incorporation of nitrile groups into fine chemicals is of particular interest through C(sp3)-H bonds activation of alkyl nitriles in the synthetic chemistry due to the highly efficient atom economy. However, the direct α-functionalization of alkyl nitriles is usually limited to its enolate chemistry. Here we report an electro-oxidative C(sp3)-H bond functionalization of acetonitrile with aromatic/aliphatic mercaptans for the synthesis of sulfur-containing ß-enaminonitrile derivatives. These tetrasubstituted olefin products are stereoselectively synthesized and the stereoselectivity is enhanced in the presence of a phosphine oxide catalyst. With iodide as a redox catalyst, activation of C(sp3)-H bond to produce cyanomethyl radicals proceeds smoothly at a decreased anodic potential, and thus highly chemoselective formation of C-S bonds and enamines is achieved. Importantly, the process is carried out at ambient temperature and can be easily scaled up.

Rh(iii)-catalyzed regioselective intermolecular N-methylene Csp3-H bond carbenoid insertion.

A Rh(iii)-catalyzed regioselective intermolecular carbenoid insertion into the N-methylene Csp3-H bond of acyclic aliphatic amides has been achieved, taking advantage of bidentate-chelation assistance. This methodology has been successfully applied to a broad range of linear and branched-chain N-alkylamides, thus providing a practical method for the assembly of diverse beta-amino esters. Mechanism studies and density functional theory (DFT) calculations revealed that a singlet Fischer type carbene insertion via an outer-sphere pathway was involved in this N-methylene Csp3-H bond carbenoid insertion.