Aaron J. Bloomfield

Room temperature, palladium-mediated P-arylation of secondary phosphine oxides.

We show that a broad range of aryl iodides are efficiently coupled with secondary phosphine oxides using 1 mol % of a catalyst formed in situ from tris(dibenzylideneacetone)dipalladium and Xantphos (1). Scalemic (S)-methylphenylphosphine oxide [(S)-2e] is shown to undergo arylation without detectable stereoerosion. The application of this method to the synthesis of novel P-chiral phosphines and PCP ligands is demonstrated.

Capture of CO2 by a Cationic Nickel(I) Complex in the Gas Phase and Characterization of the Bound, Activated CO2 Molecule by Cryogenic Ion Vibrational Predissociation Spectroscopy

We describe a systematic method for the preparation and spectroscopic characterization of a CO2 molecule coordinated to an activated bisphenoidal nickel(I) compound containing a tetraazamacrocyclic ligand in the gas phase. The resulting complex was then structurally characterized by using mass-selected vibrational predissociation spectroscopy. The results indicate that a highly distorted CO2 molecule is bound to the metal center in an η(2)-C,O coordination mode, thus establishing an efficient and rational method for the preparation of metal-activated CO2 for further studies using ion chemistry techniques.

Real-time kinetics of surfactant molecule transfer between emulsion particles probed by in situ second harmonic generation spectroscopy.

Emulsions are widely used in industrial and environmental remediation applications. The breaking and reformulation of emulsions, which occur during their use, lead to changes in their surface composition as well as their physical and chemical properties. Hence, a fundamental understanding of the transfer of surfactant molecules between emulsion particles is required for optimization of their applications. However, such an understanding remains elusive because of the lack of in situ and real-time surface-specific techniques. To address this, we designed and synthesized the surfactant probe molecules MG-butyl-1 (2) and MG-octyl-1 (3), which contain an n-butyl and an n-octyl chain, respectively, and a charged headgroup similar to that in malachite green (MG, 1). MG is known to be effective in generating second harmonic generation (SHG) signals when adsorbed onto surfaces of colloidal microparticles. Making use of the coherent nature of SHG, we monitored in real-time the transfer of 2 and 3 between oil-in-water emulsion particles with diameters of ~220 nm. We found that 3 is transferred ~600 times slower than 2, suggesting that an increase in the hydrophobic chain length decreases the transfer rate. Our results show that SHG combined with molecular design and synthesis of surfactant probe molecules can be used to measure the rate of surfactant transfer between emulsion particles. This method provides an experimental framework for examining the factors controlling the kinetics of surfactant transfer between emulsion particles, which cannot be readily investigated in situ and in real-time using conventional methods.

A heterogeneous water oxidation catalyst from dicobalt octacarbonyl and 1,2-bis(diphenylphosphino)ethane

We report the thermal synthesis of a heterogeneous Co–phosphine-based water oxidation catalyst that can be easily coated onto a variety of substrates. The system is active in neutral water and performs best with borate as electrolyte, in which the onset of catalytic current occurs at 1.51 V vs. RHE, with a Tafel slope of 68 mV per decade. Stable water oxidation is observed for over 40 hours; including in seawater with borate electrolyte, in which the catalyst is selective for water oxidation over chloride (85% Faradaic efficiency). The organic portion of the catalyst appears to play a crucial role in catalytic activity.

A switchable route to valuable commodity chemicals from glycerol via electrocatalytic oxidation with an earth abundant metal oxidation catalyst

Electrocatalytic upgrading of glycerol to value-added commodity is demonstrated using an ultralow loading of a cobalt-based oxidation catalyst at 16 μg cm−2. Reactions take place under ambient conditions in an aqueous environment, while generating H2 as a byproduct. Selectivity towards two major products, lactic acid and glyceric acid, can be controlled via simple variation of reaction conditions. The system is scalable and functions well even in the presence of methanol, an impurity commonly found in the industrial bio-diesel waste stream. Industrial glycerol waste from a local bio-diesel plant was also shown to be upgradable after a simple aqueous pretreatment.

Organometallic Iridium Complex Containing a Dianionic, Tridentate, Mixed Organic–Inorganic Ligand

A pentamethylcyclopentadienyl-iridium complex containing a tricyclic, dianionic, tridentate, scorpionate (facial binding), mixed organic-inorganic ligand was synthesized and characterized by single-crystal X-ray crystallography, as well as polynuclear NMR, UV-vis, and IR spectroscopies. The central cycle of the tridentate ligand consists of a modified boroxine in which two of the boron centers are tetrahedral, anionic borates. The complex is stable to hydrolysis in aqueous solution for >9 weeks at 25 °C but reacts with a 50 mM solution of sodium periodate within 12 s to form a periodate-driven oxygen evolution catalyst that has a turnover frquency of >15 s(-1). However, the catalyst is almost completely deactivated within 5 min, achieving an average turnover number of ca. 2500 molecules of oxygen per atom of iridium. Nanoparticles were not observed on this time scale but did form within 4 h of catalyst activation under these experimental conditions. The parent complex was modeled using density functional theory, which accurately reflected the geometry of the complex and indicated significant interaction of iridium- and boracycle-centered orbitals.

Facile solvolysis of a surprisingly twisted tertiary amide

A bicyclo[2.2.2]octane derivative containing both a tertiary amide and a methyl ester (1) was shown crystallographically to adopt a conformation in which the amide is in the cis configuration, which is sterically disfavored, but electronically favored. The steric strain induces a significant torsion (15.9°) of the amide, thereby greatly increasing the solvolytic lability of the amide to the extent that we see competitive amide solvolysis in the presence of the normally more labile methyl ester also present in the molecule.