Efficient α-Alkylation of Arylacetonitriles with Secondary Alcohols Catalyzed by a Phosphine-Free Air-Stable Iridium(III) Complex

Nickel-Catalyzed α-Alkylation of Arylacetonitriles with Challenging Secondary Alcohols

Nickel(II) complex 1 was utilized as a sustainable catalyst for α-alkylation of arylacetonitriles with challenging secondary alcohols. Arylacetonitriles with a wide range of functional groups were tolerated, and various cyclic and acyclic secondary alcohols were utilized to yield a large number of α-alkylated products. The plausible mechanism involves the base-promoted activation of precatalyst 1 to an active catalyst 2 (dehydrochlorinated product) which activates the O-H and C-H bonds of the secondary alcohol in a dehydrogenative pathway.

Oxygen-Dependent Ligand-Controlled Iron-Catalyzed Chemoselective Synthesis of Olefins and Vinyl Nitriles

An oxygen-dependent ligand-controlled chemoselective synthesis of vinyl nitriles and E-olefins by coupling a variety of alcohols and benzyl cyanides, catalyzed by a well-characterized, air-stable, easy-to-prepare Fe(II) catalyst (1a) bearing a redox-active arylazo pincer (L1a) is reported. The azo-moiety of the ligand backbone acts as an electron and hydrogen reservoir, enabling catalyst 1a to efficiently produce a broad spectrum of vinyl nitriles and E-olefins in moderate to good yields selectively under an oxygen and argon atmosphere, respectively.

Amine-functionalized bifunctional CoIII-NHC complexes: highly effective phosphine-free catalysts for the α-alkylation of nitriles

Newly developed amine functionalized NHC-supported CoIII-complexes have been identified as highly effective bifunctional catalysts for the α-alkylation of nitriles using a plethora of alcohols, ranging from aliphatic to aromatic and intriguingly, also secondary ones. Comparison of their activities with the non-bifunctional analogues uncovered their extremely high activities although possessing the high-valent CoIII-center due to metal-ligand cooperativity, which has been established by an array of control experiments.

Heteroditopic NHC Ligand Supported Manganese(I) Complexes: Synthesis, Characterization, and Activity as Non-bifunctional Phosphine-Free Catalyst for the α-Alkylation of Nitriles

In the present work, several manganese(I) complexes of chelating heteroditopic ligands Mn1-3, featuring ImNHC (imidazol-2-ylidene) connected to a 1,2,3-triazole-N or tzNHC (1,2,3-triazol-5-ylidene) donors via a methylene spacer, with possible modifications at the triazole backbone have been synthesized and completely characterized. Notably, the CO stretching frequencies, electrochemical analysis, and frontier orbital analysis certainly suggest that the chelating ImNHC-tzNHC ligands have stronger donation capabilities than the related ImNHC-Ntz ligand in the synthesized complexes. Moreover, these well-defined phosphine-free Mn(I)-NHC complexes have been found to be effective non-bifunctional catalysts for the α-alkylation of nitriles using alcohols and importantly, the catalyst Mn1 containing ImNHC connected to a weaker triazole-N donor displayed higher activity compared to Mn2/Mn3 containing an unsymmetrical bis-carbene donors (ImNHC and tzNHC). A wide range of aryl nitriles were coupled with diverse (hetero)aromatic as well as aliphatic alcohols to get the corresponding products in good to excellent yields (32 examples, up to 95 % yield). The detailed mechanistic studies including deuterium labelling experiments reveal that the reaction follows a Borrowing Hydrogen pathway.

Recent Developments in Reactions and Catalysis of Protic Pyrazole Complexes

Protic pyrazoles (N-unsubstituted pyrazoles) have been versatile ligands in various fields, such as materials chemistry and homogeneous catalysis, owing to their proton-responsive nature. This review provides an overview of the reactivities of protic pyrazole complexes. The coordination chemistry of pincer-type 2,6-bis(1H-pyrazol-3-yl)pyridines is first surveyed as a class of compounds for which significant advances have made in the last decade. The stoichiometric reactivities of protic pyrazole complexes with inorganic nitrogenous compounds are then described, which possibly relates to the inorganic nitrogen cycle in nature. The last part of this article is devoted to outlining the catalytic application of protic pyrazole complexes, emphasizing the mechanistic aspect. The role of the NH group in the protic pyrazole ligand and resulting metal-ligand cooperation in these transformations are discussed.

Manganese-Catalyzed Chemoselective Hydrosilylation of Nitroarenes: Sustainable Route to Aromatic Amines

Herein we report efficient catalytic hydrosilylations of nitroarenes to form the corresponding aromatic amines using a well-defined manganese(II)-NNO pincer complex with a low catalyst loading (1 mol %) under solvent-free conditions. This base-metal-catalyzed hydrosilylation is an easy and sustainable alternative to classical hydrogenation. A large variety of nitroarenes bearing various functionalities were selectively transformed into the corresponding aromatic amines in good yields. The potential utility of the present catalytic protocol was demonstrated by the preparation of commercial drug molecules.

An experimental and computational study of new spiro-barbituric acid pyrazoline scaffolds: restricted rotation vs. annular tautomerism

A regioselective [3+2] cycloaddition (32CA) reaction to synthesize unsymmetric spiro-barbituric pyrazolines containing a chromone or phenolic pyrazole moiety was achieved, providing good to excellent yields.