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The utilization of formic acid as a liquid organic hydrogen carrier has taken a vast interest lately because of several desirable properties. The state-of-the-art homogenous catalysts known for formic acid dehydrogenation are mainly based on noble metals such as iridium or ruthenium. 3d metals are considered to be an attractive alternative due to their abundance and low toxicity. Exploration of 3d metals has achieved exciting results mainly with iron-based catalysts; however, manganese has not received much attention, and only a few examples are available. Here we report a manganese complex [Mn(PN3P)(CO) 2 ]Br containing a pincer backbone, as an efficient catalyst for formic acid dehydrogenation. Under the optimized condition, the complex afforded a TON of 15,200. To the best of our knowledge, this is considered one of the best TON achieved using a manganese-based complex with excellent selectivity. Mechanistic studies suggested that the imine arm participates in the formic acid activation/deprotonation step, emphasizing the importance of metal-ligand cooperativity during substrate activation to promote catalytic efficacy. • A phosphorus–nitrogen PN3P–Mn pincer complex catalyzes formic acid dehydrogenation. • Good reactivity (TOF), stability (TON), and selectivity were achieved. • The metal-ligand cooperation was involved during formic acid activation. • Mechanistic insights were supported by NMR and kinetic isotope effect. [ABSTRACT FROM AUTHOR]

A wide range of desirable properties has made formic acid (FA) a favored liquid organic hydrogen carrier in recent years. The state-of-the-art homogenous catalysts generally require a base as an additive in a certain solvent to promote FA dehydrogenation. However, it is crucially important to carry out the reaction without the use of a solvent or any volatile additive in order to achieve optimal efficiency in the process. Herein, we report a series of iridium compounds having an azocarboxamide ligand backbone capable of decomposing FA exclusively into H2 and CO2 without the need to use solvents or volatile additives. Under the optimized reaction conditions, a maximum TOF of 12,500 h-1 was achieved with no formation of CO. [ABSTRACT FROM AUTHOR]

The storage and utilization of low‐carbon electricity and decarbonization of transportation are essential components for the future energy transition into a low‐carbon economy. While hydrogen has been identified as a potential energy carrier, the lack of viable technologies for safe and efficient storage and transportation of H2 greatly limits its applications and deployment at scale. Formic acid (FA) is considered one of the promising H2 energy carriers because of its high volumetric H2 storage capacity of 53 g H2/L, and relatively low toxicity and flammability for convenient and low‐cost storage and transportation. FA can be employed to generate electricity either in direct FA fuel cells (FCs) or indirectly as an H2 source for hydrogen FCs. FA can enable large‐scale chemical H2 storage to eliminate energy‐intensive and expensive processes for H2 liquefaction and compression and thus to achieve higher efficiency and broader utilization. This perspective summarizes recent advances in catalyst development for selective dehydrogenation of FA and high‐pressure H2 production. The advantages and limitations of FA‐to‐power options are highlighted. Existing life cycle assessment (LCA) and economic analysis studies are reviewed to discuss the feasibility and future potential of FA as a fuel. [ABSTRACT FROM AUTHOR]

The diruthenium(II,II) complex [Ru2(L¹)(OAc)3]Cl (1), spanned by a naphthyridine-diimine ligand and bridged by three acetates, has been synthesized. The catalytic efficacy of complex 1 has been evaluated for the acceptorless dehydrogenation (AD) of alcohols and for the dehydrogenative coupling reactions of alcohols with Wittig reagents. The diruthenium(II,II) complex is an excellent catalyst for AD of a diverse range of alcohols, and it is shown to be particularly effective for the conversion of primary alcohols to the corresponding aldehydes without undesired side products such as esters. Triphenylphosphonium ylides in a one-pot reaction with alcohols afforded the corresponding olefins in high yields with excellent E selectivity. The liberated dihydrogen gas was identified and measured to be 1 equiv with respect to alcohol. Deuteration studies with PhCD2OH revealed the absence of isotope scrambling in the product, indicating the involvement of a Ru-monohydride intermediate. Kinetic studies and DFT calculations suggest a low-energy bimetallic β-hydride elimination pathway where rate-limiting intramolecular proton transfer from alcohol to metal-bound hydride constitutes the dehydrogenation step. The general utility of metal-metal bonded compounds for alcohol AD and subsequent coupling reactions is demonstrated here. [ABSTRACT FROM AUTHOR]

Formic acid (FA) has been well recognized as one of the most promising hydrogen carriers. The dehydrogenation of the FA could offer an efficient process to on-demand hydrogen generation with a suitable catalyst. Homogeneous catalysts have demonstrated superior activity and selectivity compared to traditional heterogeneous catalysis. However, the latter is preferred for large-scale applications. By incorporating the homogeneous organometallic complex onto an appropriate support, the unique features of both types of catalysts can be combined and utilized effectively. Herein, we synthesized an immobilized PN3P-Ir pincer catalyst (2) supported onto KCC-1, a 3D fibrous silica nanosphere that exhibits a high surface area and contains a tetracoordinate aluminum site. To reduce the use of volatile additives, the choice of cesium formate (CsO 2 CH) was found to be crucial as at 80–90 °C, CsO 2 CH could act as a reaction medium and serve as basic additive. Remarkable reactivities under neat conditions were achieved with a TOF of 13,290 h-1 and a TON of up to 540,000. The comparative study indicates a significant improvement of 2 from its homogenous counterpart, PN3P-IrH 3 (1). Neat Formic Acid Dehydrogenation: The synthesized immobilized PN3P pincer iridium catalyst (2) showed remarkable reactivity under neat conditions to achieve a TOF of 13,290 h-1 and TON up to 540,000 compared to a homogenous PN3P pincer iridium catalyst (1). Cesium formate (CsO 2 CH) was found to act as a molten matrix and serve as both solvent and basic additive in the formic acid dehydrogenation. The overall study revealed that 2 shows superior activity, selectivity, and stability for the neat formic acid dehydrogenation. [Display omitted] • CsO 2 CH acts as both solvent and basic additive. • The larger negative charge on immobilized PN3P-Ir improves the formic acid dehydrogenation activity. [ABSTRACT FROM AUTHOR]

All yields are determined by GC-MS-analysis with dodecane as internal standard. [ABSTRACT FROM AUTHOR]