Luca Gonsalvi

In the quest for cheap and abundant feedstocks for sustainable hydrogen production, glycerol is emerging as a cost-effective, promising liquid organic hydrogen-rich carrier (LOHC) that can be catalytically activated to produce hydrogen alongside valuable organic products. Selective catalytic acceptorless dehydrogenation of glycerol to lactate and hydrogen gas was achieved with a maximum turnover number (TON_max) of ca. 1600, using a pincer-type ruthenium(II) complex bearing a bis(aminophosphine)pyridine PN³P ligand as a homogeneous catalyst under moderate reaction conditions (24 h, 140 °C) in the presence of KOH as base. NMR experiments and DFT calculations provided insights into key steps of the catalytic process and the energetics of the proposed reaction pathway.

In the quest for highly active ruthenium(II) complexes for homogeneous catalytic CO2 hydrogenation to formate, a small library of cationic Ru(k3-tpm) complexes [tpm = tris(pyrazolyl)methane], bearing different ancillary ligands, were tested under various reaction conditions, with and without the addition of a Lewis acid co-catalyst. Under optimized conditions (80 bar, 120 °C) and in the presence of LiOTf, TONs > 54000 were obtained in single batch runs with the complex [RuCl(k3-tpm)(PPh3)(CH3CN)]Cl (1). Mechanistic studies using NMR spectroscopy and DFT calculations were also carried out to elucidate key steps and the energies associated with the reaction pathway, which allowed for the proposal of a catalytic mechanism.

In the quest for sustainable hydrogen production, the use of biomass‐derived feedstock is gaining importance. Acceptorless Dehydrogenation (AD) in the presence of efficient and selective catalysts has been explored worldwide as a suitable method to produce hydrogen from hydrogen‐rich simple organic molecules. Among these, glycerol and sugars have the advantage of being inexpensive, abundant, and obtainable from fatty acid basic hydrolysis (biodiesel industry) and from biomass by biochemical and thermochemical processing, respectively. Although heterogeneous catalysts are more widely used for hydrogen production from biomass‐based feedstock, the harsh reaction conditions often limit their applicability due to the deactivation of active sites caused by the coking of carbonaceous materials. Moreover, heterogeneous catalysts are more difficult to fine‐tune than homogeneous counterparts, and the latter also allow for high process selectivities under milder conditions. The present Concept article summarizes the main features of the most active homogeneous catalysts reported for glycerol and monosaccharides AD. In order to directly compare hydrogen production efficiencies, the choice of literature works was limited to reports where hydrogen was clearly quantified by yields and turnover numbers (TONs). The types of transition metals and ligands are discussed, together with a perspective view on future challenges of homogeneous AD reactions for practical applications.

Herein, I would like to provide an overview of this Special Issue, published in the Organic and Polymer Chemistry Section of Catalysis, comprising contributions from 18 of the journal’s Editorial Board Members

The catalytic activation of carbon dioxide (CO₂) can be a promising tool for the use of this abundant, non‐flammable and non‐toxic gas as feedstock for C1 chemical synthesis, in particular for bulk products such as formic acid (HCOOH) and methanol (CH₃OH). The key for successful, widespread use of CO₂ is the design and application of efficient, thermally robust and cheap catalysts. In the last decade, the use of earth‐abundant transition metal complexes, in particular those of 3d metals, has shown promising results. In this review article, a comprehensive summary of the main catalytic systems described in the literature for homogeneous Mn(I)‐catalyzed CO₂ reduction processes (hydrogenation, hydroboration and hydrosilylation) will be described, with particular attention to the effect of stabilizing ligands, reaction conditions and need for additives, together with mechanistic details often obtained by a combination of experimental data and DFT calculations.

CO₂ catalytic hydrogenation to formate was achieved (TON_max=ca. 3800) in the presence of the neutral, halide‐free, coordinatively saturated tris(carbonyl) manganese pincer‐type complex [Mn(PNP)(CO)₃], bearing a diarylamido pincer‐type PNP ligand, using DBU as base and LiOTf as Lewis acid additive, under mild reaction conditions (60 bar, 80 °C). DFT calculations suggest that the precatalyst activation key step occurs by intermolecular, base assisted dihydrogen heterolytic splitting rather than by the expected ligand‐assisted intramolecular MLC‐type mechanism.

The new bimetallic [Ru₂(μ‐Cl)₃(CAP)₆]Cl (1) and monometallic cis,cis,trans‐[RuCl₂(dmso‐S)₂(CAP)₂] (2) complexes, bearing the water soluble cage‐like phosphine CAP (1,4,7‐triaza‐9‐phosphatricyclo[5.3.2.1]tridecane), were synthesized and characterized in solution by NMR spectroscopy and ESI‐MS spectrometry. The complexes, endowed with high solubility and stability in water, were applied as catalysts for the proof‐of‐concept hydration of benzonitrile to benzamide in neat water at 100 °C, achieving high conversions with only 1 mol % of catalyst, both in single runs and in catalyst recycling experiments.