Direct asymmetric hydrogenation (AH) and asymmetric transfer hydrogenation (ATH) reactions are among the most efficient approaches to produce chiral building blocks. Recently, these types of transformations have witnessed a shift towards the use of molecular catalysts based on earth-abundant transition metals due to their ready availability, economic advantage, and novel properties. With particular regard to manganese, catalyst development has seen both the efficiency and substrate scope in AH and ATH greatly improved, with the emergence of a large number of well-defined Mn-complexes employed in this field. The reaction scope includes the AH and ATH of C=O bonds, asymmetric reduction of C=N bonds and the asymmetric reductive transformations of C=C bonds. Herein, our survey of the area focuses on the catalytic activity of such complexes, their versatility towards asymmetric transformations and the routes employed to convert substrates to their target molecules. We consider the collected findings of this article will be helpful to the reader by providing an insight into ligand design, thereby aiding future catalyst development. Moreover, this review is aimed at highlighting the remarkable progress made in the last six years in the development of manganese complexes for enantioselective reduction.

Ruthenium nanoparticles stabilised by an amine-modified Ordered Mesoporous Silica Immobilized Ionic Liquid (OMSIIL) are efficient catalysts for the partial reduction of nitrobenzene to hydrazobenzene with 100% selectivity as well as the complete reduction to aniline. High selectivity for the partial reduction of nitrobenzene to hydrazobenzene was obtained when the reaction was conducted in ethanol with 0.5 mol% catalyst and NaBH4 as the hydrogen donor whereas aniline was obtained as the sole product in water when dimethylamine borane (DMAB) was used as the hydrogen donor. Interestingly, while a range of electron poor nitroarenes were reduced to the corresponding hydrazoarene with high selectivities and good conversions, nitroarenes substituted with electron donating groups resulted in complete reduction to the aniline. Composition-time profiles suggest that reductions conducted in ethanol with sodium borohydride occur via the condensation pathway while those conducted in water using dimethylamine borane as the hydrogen source may well go via the direct pathway. This is the first example of the selective reduction of nitrobenzene to hydrazobenzene using a ruthenium nanoparticle-based catalyst and the initial TOF of 320 mol nitrobenzene converted mol Ru-1 h-1 is markedly higher than previous literature reports.

The selective oxidation of lower olefins over bismuth molybdate based multicomponent catalysts are key reactions in chemical industry for the functionalization of hydrocarbons. To understand the catalysts’ working principles, three Bi−Mo−Co−Fe-oxides were synthesized, tested in the selective oxidation of propylene and isobutene and characterized by complementary Raman spectroscopy, X-ray absorption spectroscopy and synchrotron X-ray diffraction. Comparison of their catalytic behavior in both reactions provided fundamental insights into the corresponding structure-activity correlations.

Abstract

The elucidation of structure-activity correlations in selective oxidation of propylene and isobutene over mixed metal oxides (MMO) is attractive for knowledge-based catalyst design and process optimisation. Particularly, 4-component Bi−Mo−Co−Fe−O catalysts need to be studied since their complex metal oxide phase mixture leads to higher activity and selectivity than 2-component Bi−Mo−O. Hence, three Bi−Mo−Co−Fe-oxides with different metal ratios were prepared by hydrothermal synthesis and compared during selective oxidation tests with propylene and isobutene. The active phases after several days on stream were investigated by synchrotron X-ray diffraction (XRD) and Raman spectroscopy, while the structural evolution under reaction conditions was followed by operando Raman spectroscopy, synchrotron XRD, and multi-edge X-ray absorption spectroscopy. Similar structural transformations were observed during selective oxidation of propylene and isobutene, with similar influence on catalytic performance. A phase mixture of β-CoMoO₄/β-Co_0.7Fe_0.3MoO₄, γ-Bi₂MoO₆, Fe₃O₄ and Bi₃FeMo₂O₁₂ was observed, whereby high amounts of β-CoMoO₄/β-Co_0.7Fe_0.3MoO₄ increased selectivity to acrolein/methacrolein. In contrast, high amounts of γ-Bi₂MoO₆ and Fe₃O₄ favoured total oxidation to CO and CO₂. The simultaneous presence of β-CoMoO₄/β-Co_0.7Fe_0.3MoO₄, Bi₃FeMo₂O₁₂ and Fe₂O₃ increased selectivity to methacrolein in isobutene oxidation, whereas no comparative increase in acrolein selectivity was observed in propylene oxidation. This suggests different key active phases in both reactions.

N-heterocyclic carbene-catalyzed cross-coupling reaction has been recognized as an enabling tool in the synthesis of complex ketones in recent years. This strategy enables the direct acylation of various alkyl halides under an organocatalytic system.

Abstract

During the past decades, N-heterocyclic carbene (NHC)-catalyzed reactions have emerged as a versatile tool in synthetic chemistry. In particular, NHC-catalyzed cross-coupling reaction has been significantly developed in many respects, including new reaction development and mechanistic investigation. This concept article presents recent advances towards direct cross-coupling reactions of aldehydes with alkyl halides enabled by NHC organocatalysis.

As an excellent class of electrode materials, carbon-based materials have garnered sustained attention. Constructing carbon-based skeleton with unique structure has become a vital research area in the fields of electrocatalysis. Recently, surface curvature has been extensive discussed as a compelling factor in electronic modulation for electrocatalyst design. Benefitting from its distinctive regulation, the intrinsic activity and service stability of catalysts during electrocatalytic process can be significantly improved. Therefore, a helical structure that adeptly integrates well-regulated, highly ordered surface curvatures is considered to be of great research value for the synthesis of carbon-based skeleton. In this Concept article, we systematically summarize the up-to-date reports on the synthetic methods of carbon-based skeletons with helical structures and present major challenges in this field. We also emphasize that the helical carbon-based skeleton could be combined with transition metals for cooperative coupling, potentially leading to the further development of high-efficiency electrocatalysts.