Metal-ligand cooperativity (MLC) is an established strategy for developing effective hydrogenation and dehydrogenation catalysts. Metal-metal cooperativity (MMC) in bimetallic complexes is not as well understood, and to date has had limited implementation in (de)hydrogenation. Herein we use (de)hydrogenation processes as a platform to examine modes of cooperativity, with a particular focus on catalytic mechanisms. We investigate how lessons learnt from the extensive development of metal-ligand cooperative catalysts can aid the ongoing development of metal-metal cooperative catalysts.

Cooperative approaches in catalytic hydrogenation and dehydrogenation.

Electronically tuneable orthometalated Ru<sup>II</sup>–NHC complexes as efficient catalysts for C–C and C–N bond formations <i>via</i> borrowing hydrogen strategy

Electronically Tuneable Orthometalated RuII-NHC Complexes as Efficient Catalysts for the C-C and C-N Bond Formations via Borrowing Hydrogen Strategy

Acceptorless dehydrogenative coupling (ADC) of alcohols and water/hydroxides is an emergent and graceful approach to produce carboxylic acids. Therefore, it is of high demand to develop active and practical catalysts/catalytic systems for this attractive transformation. Herein, we designed and fabricated a series of cyclometallated N-heterocyclic carbene-Ru (NHC-Ru) complexes via ligand tuning of [Ru-1], the superior complex in our previous work. Gratifyingly, gram-scale synthesis of carboxylic acids was efficiently enabled at an ultralow Ru loading (62.5 ppm) in open air. Moreover, effects of distinct ancillary NHC ligands and other parameters on this catalytic process were thoroughly studied, while further systematic studies were carried out to provide rationales for the activity trend of [Ru-1]-[Ru-7]. Finally, determination of quantitative green metrics illustrated that the present work exhibited superiority over representative literature reports. Hopefully, this study could provide valuable input for researchers who are engaging in metal-catalyzed ADC reactions.

Gram-scale synthesis of carboxylic acids via catalytic acceptorless dehydrogenative coupling of alcohols and hydroxides at an ultralow Ru loading

Acceptorless dehydrogenative coupling (ADC) of alcohols and water/hydroxides is an emergent and graceful approach to produce carboxylic acids. Therefore, it is of high demand to develop active and practical catalysts/catalytic systems for this attractive transformation. Herein, we designed and fabricated a series of cyclometallated N-heterocyclic carbene-Ru (NHC-Ru) complexes via ligand tuning of [Ru-1], the superior complex in our previous work. Gratifyingly, gram-scale synthesis of carboxylic acids was efficiently enabled at an ultralow Ru loading (62.5 ppm) in open air. Moreover, effects of distinct ancillary NHC ligands and other parameters on this catalytic process were thoroughly studied, while further systematic studies were carried out to provide rationales for the activity trend of [Ru-1]-[Ru-7]. Finally, determination of quantitative green metrics illustrated that the present work exhibited superiority over representative literature reports. Hopefully, this study could provide valuable input for researchers who are engaging in metal-catalyzed ADC reactions. 

Recent advances on N-heterocyclic carbene transition metal complexes for dehydrogenative catalysis using alcohols

Bifunctional Effect of a Triple-Bond Heterobimetallic Zr/Co System for Hydrogen Activation

Bifunctional transition metal complexes are of particular interest in metal-ligand cooperative activation of small molecules. As a novel type of bifunctional catalyst, Lewis acid transition metal (LA-TM) complexes have attracted increasing interest in hydrogen activation and storage. To advance the catalyst design, herein the metal effect of LA-TM complexes on the hydrogen activation has been systematically studied with a series of tris(phosphino)borane (TPB) complexes with V, Cr, Mn, Fe, Co, and Ni as metal centers. The metal effect not only influences the mechanism of hydrogen activation, but also notably casts a volcano plot for the activity. TPB complexes of V, Cr, Mn, Fe, and Co tend to activate H2 through a stepwise mechanism, while TPB-Ni prefers a synergetic mechanism for H2 activation. More importantly, the metal effect significantly influences the activity of H2 activation and the formation of the LA-H-TM bridging hydride. The trend of changes in the LA-H-TM structures, the second-order perturbation stabilization energies, and the Laplacian bond orders, along with different metals (from V to Ni), are all interestingly constitute volcano plots for the performance of TPB-TM complexes catalyzed H2 activation. TPB-Mn and TPB-Fe are found to be the optimal catalysts among the discussed TPB-TM complexes. The volcano plots disclosed for the metal effects should be informative and instructive for homogeneous and heterogeneous LA-TM catalysts development.

Peifeng Su

Papers

Recent advances on N-heterocyclic carbene transition metal complexes for dehydrogenative catalysis using alcohols

Bifunctional Effect of a Triple-Bond Heterobimetallic Zr/Co System for Hydrogen Activation

Metal Effect Meets Volcano Plots: A DFT Study on Tris(phosphino)borane-Transition Metal Complexes Catalyzed H2 Activation.