We report a ruthenium complex containing an N,N'-diimine ligand for the selective decomposition of formic acid to H and CO in water in the absence of any organic additives. A turnover frequency of 12 000 h and a turnover number of 350 000 at 90 °C were achieved in the HCOOH/HCOONa aqueous solution. Efficient production of high-pressure H and CO (24.0 MPa (3480 psi)) was achieved through the decomposition of formic acid with no formation of CO. Mechanistic studies by NMR and DFT calculations indicate that there may be two competitive pathways for the key hydride transfer rate-determining step in the catalytic process.

Formic acid (FA) has been extensively studied as one of the most promising hydrogen energy carriers today. The catalytic decarboxylation of FA ideally leads to the formation of CO2 and H2 that can be applied in fuel cells. A large number of transition‐metal based homogeneous catalysts with high activity and selectivity have been reported for the selective FA dehydrogentaion. In this review, we discussed the recent development of C,N/N,N‐ligand and pincer ligand‐based homogeneous catalysts for the FA dehydrogenation reaction. Some representative catalysts are further evaluated by the CON/COF assessment (catalyst on‐cost number)/(catalyst on‐cost frequency). Conclusive remarks are provided with future challenges and opportunities.

We have developed the Rh-catalyzed selective C-H functionalization of 6-arylpurines, in which the purine moiety directs the C-H bond activation of the aryl pendant. While the first C-H amination proceeds via the N1-chelation assistance, the subsequent second C-H bond activation takes advantage of an intramolecular hydrogen-bonding interaction between the initially formed amino group and one nitrogen atom, either N1 or N7, of the purinyl part. Isolation of a rhodacycle intermediate and the substrate variation studies suggest that N1 is the main active site for the C-H functionalization of both the first and second amination in 6-arylpurines, while N7 plays an essential role in controlling the degree of functionalization serving as an intramolecular hydrogen-bonding site in the second amination process. This pseudo-Curtin-Hammett situation was supported by density functional calculations, which suggest that the intramolecular hydrogen-bonding capability helps second amination by reducing the steric repulsion between the first installed ArNH and the directing group.

The CO(2) fixation ability of N-heterocyclic carbenes (NHC) has been assessed on the basis of electronic and steric properties of the N- and C-substituents, measured in terms of molecular electrostatic potential minimum, observed at the carbene lone pair region of NHC (V(min1)) as well as at the carboxylate region of the NHC-CO(2) adduct (V(min2)). Both V(min1) and V(min2) are found to be simple and efficient descriptors of the stereoelectronic effect of NHCs. The V(min)-based analysis also proved that the stereoelectronic effect of N- and C-substituents is additive. When only C-substituents are present in NHC, its CO(2) affinity solely depends on the electronic effect, whereas if the N-center bears the substituents, the steric factor plays a major role in the carboxylation/decarboxylation process. For standard substituents, maximum CO(2) binding energy of 18.0 kcal/mol is observed for the most electron-donating combination of NMe(2) as the C-substituent and Me as the N-substituent. Introduction of ring strain through five-membered ring fusion at the NC bond slightly increased the electron-rich character of the carbene lone pair and also enhanced the CO(2) binding energy to 20.9 kcal/mol. To further improve the CO(2) fixing ability of NHCs, we have proposed the use of CH(2)OH, CH(2)NHCOMe, and CH(2)NHPh as N-substituents, as they participate in intramolecular hydrogen bond interaction with the carboxylate. With the new strategy, considerable improvement in the CO(2) binding energy (26.5 to 33.0 kcal/mol) is observed.

Structural, electronic, and energetic characteristics of tricin, tricin-4'-O-(erythro-β-guaiacylglyceryl)ether (TEGE), and tricin-4'-O-(threo-β-guaiacylglyceryl)ether (TTGE), isolated from "Njavara" rice bran have been studied using DFT to explain their experimentally determined radical scavenging activity (EC(50) values) in comparison with known standards such as quercetin, myricetin, and catechin. Among the three mechanisms proposed for explaining the antioxidant activity, proton coupled-electron transfer (PC-ET), sequential proton loss electron transfer (SPLET), and electron transfer-proton transfer (ET-PT), our results support the second one. The O-H bond dissociation enthalpy (BDE) and the spin density on the oxygen with the radical character are excellent descriptors of radical scavenging activity. BDE (in kcal/mol) increased in the order myricetin (74.6) < quercetin (78.1) < catechin (78.3) < tricin (81.5) < TTGE (90.6) < TEGE (91.1), while the EC(50) increased exponentially with increase in BDE, 20.51, 42.98, 45.07, 90.39, 208.01, and 352.04 μg/mL for myricetin, quercetin, catechin, tricin, TTGE, and TEGE, respectively.