Molly O'Hagan

Dinitrogen Reduction by a Chromium(0) Complex Supported by a 16-Membered Phosphorus Macrocycle

We report a rare example of a Cr-N2 complex supported by a 16-membered phosphorus macrocycle containing pendant amine bases. Reactivity with acid afforded hydrazinium and ammonium, representing the first example of N2 reduction by a Cr-N2 complex. Computational analysis examined the thermodynamically favored protonation steps of N2 reduction with Cr leading to the formation of hydrazine.

Electrocatalytic H2 production with a turnover frequency >107 s−1: the medium provides an increase in rate but not overpotential

Rapid proton movement results in exceptionally fast electrocatalytic H2 production (up to 3 × 107 s−1) at overpotentials of ∼400 mV when catalysed by [Ni(PPh2NC6H4x2)2]2+ complexes in an acidic ionic liquid–water medium ([(DMF)H]NTf2–H2O, χH2O = 0.71).

Binuclear complexes containing a methylnickel moiety: relevance to organonickel intermediates in acetyl coenzyme A synthase catalysis.

A series of binuclear NiNi complexes supported by a single thiolate bridge and containing a methylnickel moiety have been prepared and fully characterized. The complexes represent structural analogues for the proposed organonickel intermediate in the acetyl coenzyme A synthase catalytic cycle. Variable temperature 31P NMR spectroscopy was used to examine dynamic behavior of the thiolate bridging interaction in two of the derivatives. Kinetic analyses, independent exchange and crossover experiments support an intermolecular exchange mechanism. Carbonylation results in thioester formation via a reductive elimination pathway.

A rare terminal dinitrogen complex of chromium.

Cis and trans-Cr-N(2) complexes supported by the diphosphine ligand P(Ph)(2)N(Bn)(2) have been prepared. Positioned pendant amines in the second coordination sphere influence the thermodynamically preferred geometric isomer. Electronic structure calculations indicate negligible Cr-N(2) back-bonding; rather, electronic polarization of N(2) ligand is thought to stabilize Cr-N(2) binding.

Controlling proton movement: Electrocatalytic oxidation of hydrogen by a nickel(ii) complex containing proton relays in the second and outer coordination spheres

A nickel bis(diphosphine) complex containing proton relays in the second and outer coordination spheres, Ni(P(Cy)2N((CH2)2OMe))2, (P(Cy)2N((CH2)2OMe) = 1,5-di(methoxyethyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to the Ni(II) complex results in rapid formation of three isomers of the doubly protonated Ni(0) complex, [Ni(P(Cy)2N((CH2)2OMe)2H)2](2+). The three isomers show fast interconversion at 40 °C, unique to this complex in this class of catalysts. Under conditions of 1.0 atm H2 using H2O as a base, catalytic oxidation proceeds at a turnover frequency of 5 s(-1) and an overpotential of 720 mV, as determined from the potential at half of the catalytic current. Compared to the previously reported Ni(P(Cy)2N(Bn))2 complex, the new complex operates at a faster rate and at a lower overpotential.

Controlling Proton Delivery through Catalyst Structural Dynamics

The fastest synthetic molecular catalysts for H2 production and oxidation emulate components of the active site of hydrogenases. The critical role of controlled structural dynamics is recognized for many enzymes, including hydrogenases, but is largely neglected in designing synthetic catalysts. Our results demonstrate the impact of controlling structural dynamics on H2 production rates for [Ni(PPh2 NC6H4R2 )2 ]2+ catalysts (R=n-hexyl, n-decyl, n-tetradecyl, n-octadecyl, phenyl, or cyclohexyl). The turnover frequencies correlate inversely with the rates of chair-boat ring inversion of the ligand, since this dynamic process governs protonation at either catalytically productive or non-productive sites. These results demonstrate that the dynamic processes involved in proton delivery can be controlled through modification of the outer coordination sphere, in a manner similar to the role of the protein architecture in many enzymes. As a design parameter, controlling structural dynamics can increase H2 production rates by three orders of magnitude with a minimal increase in overpotential.

Crystal structure of di­methyl­formamidium bis­(tri­fluoro­methane­sulfon­yl)amide: an ionic liquid

The cation and anion of the title salt are linked by an O—H⋯N hydrogen bond and a C—H⋯O interaction, resulting in a high viscosity and a crystallization temperature slightly lower than ambient temperature.