No abstract

The water‐soluble ruthenium(II)–mTPPTS complex (mTPPTS=meta‐trisulfonated triphenylphosphine) efficiently catalyzes the generation of hydrogen from formic acid in aqueous solution. This catalyst has been immobilized in a hydrophilic silica support to facilitate mobile portable applications. It was used in diluted formic acid solutions, in which the recycling of a liquid phase catalyst is problematic. A series of heterogenized catalysts have been prepared by the reaction of the ruthenium(II)–mTPPTS dimer and silica functionalized with diphenylphosphine groups via alkyl chains. The length of the alkylene chain separating the silica from the diphenylphosphine group has been varied in these catalysts—all of them catalyzing the decomposition of formic acid. The catalysts were easily separated from the solution and reused. The optimized catalytic system based on MCM41‐Si‐(CH2)2PPh2/Ru‐mTPPTS demonstrated an activity and stability comparable to those of the homogeneous catalyst: a turnover frequency of 2780 h−1 was obtained at 110 °C, and no ruthenium leaching was detected after turnover numbers of 71 000.

The hydrogenation of phenylacetone to cyclohexylacetone, in which the aromatic ring is selectively reduced in preference to the carbonyl group, has been achieved with chemoselectivities exceeding 90%. The catalyst (precatalyst) used to achieve this transformation comprises PVP-stabilized Rh nanoparticles dispersed in water with some phosphine ligand additives. Phosphine ligands with different steric and electronic properties and polarities were investigated for this purpose, and several clear trends were observed, showing the potential of welldefined phosphine ligands as modifiers in nanocatalysis.

The selective catalytic decomposition of formic acid into hydrogen and carbon dioxide has been achieved in water under mild conditions. For the first time, a ruthenium ion in combination with a series of oligocationic, ammoniomethyl‐substituted triarylphosphines was used for this reaction, as opposed to previously used anionic and neutral ligands. These cationic phosphines vary in size and charge and therefore have different hydrophilic, steric, and electronic properties. Excellent catalytic activities were achieved in the formic acid dehydrogenation reaction and correlations between the activity and the ligand structure were made. High turnover frequencies (TOFs) of 1950 h−1 and turnover numbers (TONs) over 10 000 were obtained through optimization of the catalytic system.

Water‐soluble ruthenium m‐triphenylphosphinetrisulfonate (TPPTS) complexes are excellent catalysts for formic acid dehydrogenation. Interestingly, the choice of metal catalyst precursor has a direct influence on initial activities. The reaction with hexaaquaruthenium(II) tosylate directly yields bisphosphine complexes in the presence of TPPTS and formic acid, whereas trisphosphine adducts are involved if the reaction starts with ruthenium(III) chloride. We present the results of a series of manometric and spectroscopic experiments that reveal the true nature of these highly active species, and subsequently propose a rational “fast” cycle mechanism explaining this peculiar activity profile.