Formic acid is a promising energy carrier for on-demand hydrogen generation. Because the reverse reaction is also feasible, formic acid is a form of stored hydrogen. Here we present a robust, reusable iridium catalyst that enables hydrogen gas release from neat formic acid. This catalysis works under mild conditions in the presence of air, is highly selective and affords millions of turnovers. While many catalysts exist for both formic acid dehydrogenation and carbon dioxide reduction, solutions to date on hydrogen gas release rely on volatile components that reduce the weight content of stored hydrogen and/or introduce fuel cell poisons. These are avoided here. The catalyst utilizes an interesting chemical mechanism, which is described on the basis of kinetic and synthetic experiments.

We prepared the primary adduct for the reaction of singlet dioxygen (1O2) with an arylphosphine by using the sterically hindered arylphosphine tris(o-methoxyphenyl)phosphine. The resulting phosphadioxirane has a dioxygen molecule triangularly bound to the phosphorus atom. Olefin trapping experiments show that the phosphadioxirane can undergo nonradical oxygen atom-transfer reactions. Under protic conditions, two different intermediates are formed during the reaction of singlet dioxygen with tris(o-methoxyphenyl)phosphine, namely, the corresponding hydroperoxy arylphosphine and a hydroxy phosphorane. Experiments with other arylphosphines possessing different electronic and steric properties demonstrate that the relative stability of the tris(o-methoxyphenyl)phosphadioxirane is due to both steric and electronic effects.

Resveratrol (1) reacts with singlet oxygen by two major pathways: A [2+2] cycloaddition forming a transient dioxetane that cleaves into the corresponding aldehydes and a [4+2] cycloaddition forming an endoperoxide that, upon heating, undergoes a rearrangement to moracin M. The rate constant by which singlet oxygen is removed by 1 (k(T)) was determined by time-resolved infrared luminescence spectroscopy to be 1.5 × 10(6) M(-1) sec(-1) in CD(3)OD, smaller than previously reported values. Chemical reaction accounts for ca. 25% of k(T).

The syntheses of novel dimethylbis(2-pyridyl)borate nickel(II) complexes 4 and 6 are reported. These complexes were unambiguously characterized by X-ray analysis. In dichloromethane solvent, complex 4 undergoes a unique square-planar to square-planar rotation around the nickel(II) center, for which activation parameters of ΔH⧧ = 12.2(1) kcal mol–1 and ΔS⧧ = 0.8(5) eu were measured via NMR inversion recovery experiments. Complex 4 was also observed to isomerize via a relatively slow ring flip: ΔH⧧ = 15.0(2) kcal mol–1; and ΔS⧧ = −4.2(7) eu. DFT studies support the experimentally measured rotation activation energy (cf. calculated ΔH⧧ = 11.1 kcal mol–1) as well as the presence of a high-energy triplet intermediate (ΔH = 8.8 kcal mol–1).

A (pyridyl)­phosphine-ligated ruthenium­(II) catalyst is reported for the chemoselective benzylic N-alkylation of amines, via a hydrogen-borrowing mechanism. The catalyst operates under mild conditions, neat, and without a base or other additive. These conditions offer remarkable functional group compatibility for applications in organic synthesis, including reactions involving phenols and anilines, which are very difficult to achieve. Mechanistic studies suggest that, unlike other catalysts for this reaction, the redox steps are fast and reversible while imine formation is slow. We perceive that this is the origin of the selectivity realized with these reaction conditions.