A simple method for the preparation of bio-inspired nickel bisdiphosphine hydrogen-evolving catalysts

International audienceWe herein report on a novel, simple and straightforward method for the preparation of nickel bisdiphosphine hydrogen-evolving catalysts, so-called DuBois catalysts, from commercially available nickel hexaaqua salts. This method yields coordination complexes with the same physical characteristics as previously described for compounds prepared from the [Ni(CH$_3$CN)$_6$]$^{2+}$ precursor. However, if hexaaquanickel(II) chloride is used as a precursor, a different nickel bisdiphosphine complex is formed, which incorporates chloride as an axial ligand. This complex displays a significantly different electrochemical behavior and a diminished activity for proton reduction as compared to classic DuBois catalysts

Molecular Cobalt Complexes with Pendant Amines for Selective Electrocatalytic Reduction of Carbon Dioxide to Formic Acid

We report here on a new series of CO2-reducing molecular catalysts based on Earth-abundant elements that are very selective for the production of formic acid in dimethylformamide (DMF)/water mixtures (Faradaic efficiency of 90 ± 10%) at moderate overpotentials (500–700 mV in DMF measured at the middle of the catalytic wave). The [CpCo(PR2NR′2)I]+ compounds contain diphosphine ligands, PR2NR′2, with two pendant amine residues that act as proton relays during CO2-reduction catalysis and tune their activity. Four different PR2NR′2 ligands with cyclohexyl or phenyl substituents on phosphorus and benzyl or phenyl substituents on nitrogen were employed, and the compound with the most electron-donating phosphine ligand and the most basic amine functions performs best among the series, with turnover frequency >1000 s–1. State-of-the-art benchmarking of catalytic performances ranks this new class of cobalt-based complexes among the most promising CO2-to-formic acid reducing catalysts developed to date; addressing the stability issues would allow further improvement. Mechanistic studies and density functional theory simulations confirmed the role of amine groups for stabilizing key intermediates through hydrogen bonding with water molecules during hydride transfer from the Co center to the CO2 molecule

Metal-controlled diastereoselective self-assembly and circularly polarized luminescence of a chiral heptanuclear europium wheel

The chiral dissymmetric tetradentate ligand (S)-6′-(4-phenyloxazolin- 2-yl)-2,2′-bipyridine-6-carboxylate (S-Phbipox) leads to the diastereoselective assembly of a homochiral Eu3+ triangle and a highly emissive (quantum yield = 27%) heptanuclear wheel that is the largest example of a chiral luminescent complex of Eu3+ reported to date. The nuclearity of the assembly is controlled by the solvent and the Eu3+ cation. All of the compounds show large circularly polarized luminescence with an activity that varies with the nature of the assembly (highest for the homochiral trimer). © 2012 American Chemical Society