Synthetic Exploration of Bis(phenolate) Aza-BODIPYs and Heavier Group 13 Chelates.

A series of boron, aluminum, gallium, and indium chelates containing the underexplored bis(phenolate) aza-dipyrromethene (aza-DIPY) core were prepared. These compounds were found to possess near-infrared absorption and emission profiles in the 710 to 770 nm domain and exhibit quantum yield values up to 14%. X-ray diffraction analysis revealed that heavier group 13 bis(phenolate) aza-DIPY chelates possessed octahedral geometries with either THF or pyridine groups occupying the axial positions as opposed to the tetrahedral geometry of the boron chelate.

Why Do N-Alkylated Anilides Bend Over? The Factors Dictating the Divergent Conformational Preferences of 2° and 3° N-Aryl Amides.

The conformational preferences of 28 sterically and electronically diverse N-aryl amides were determined using density functional theory (DFT), using the B3LYP functional and 6-31G(d) basis set. For each compound, both the cis and trans conformers were optimized, and the difference in ground state energy calculated. For six of the compounds, the potential energy surface was determined as a function of rotation about the N-aryl bond (by 5° increments) for both cis and trans conformers. A natural bond orbital (NBO) deletion strategy was also employed to determine the extent of the contribution of conjugation to the energies of each of the conformers. By comparing these computational results with previously reported experimental data, an explanation for the divergent conformational preferences of 2° N-aryl amides and 3° N-alkyl-N-aryl amides was formulated. This explanation accounts for the observed relationships of both steric and electronic factors determining the geometry of the optimum conformation, and the magnitude of the energetic difference between cis and trans conformers: except under the most extreme scenarios, 2° amides maintain a trans conformation, and the N-bound arene lies in the same plane as the amide unless it has ortho substituents; for 3° N-alkyl-N-aryl amides in which the alkyl and aryl substituents are connected in a small ring, trans conformations are also favored, for most cases other than formamides, and the arene and amide remain in conjugation; and for 3° N-alkyl-N-aryl amides in which the alkyl and aryl substituents are not connected in a small ring, allylic strain between the two N-bound substituents forces the aryl substituent to rotate out of the plane of the amide, and the trans conformation is destabilized with respect to the cis conformation due to repulsion between the π system of the arene and the lone pairs on the oxygen atom of the carbonyl. The cis conformation is increasingly more stable than the trans conformation as electron density is increased on the arene because the more electron-rich arenes adopt a more orthogonal arrangement, increasing the interaction with the carbonyl oxygen, while simultaneously increasing the magnitude of the repulsion due to the increased electron density in the π system. The trans conformation is favored for 2° amides even when the arene is orthogonal to the amide, in nearly all cases, because the C-N-C bond angle can expend at the expense of the C-N-H bond angles, while this is not favorable for 3° amides.

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.

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.

[3 + 2] Cycloadditions of Tertiary Amine N-Oxides and Silyl Imines as an Innovative Route to 1,2-Diamines.

We have developed a one-pot synthetic method for producing 1,2-diamines from easily prepared and commercially available precursors through a formal umpolung process. Our method utilizes an efficient [3 + 2] cycloaddition as the key step in forming substituted 1,2-diamines in moderate to high yields. These resulting compounds can undergo subsequent transformations, demonstrating their utility as synthetic building blocks for more complex scaffolds. Finally, we propose a reasonable mechanism for this transformation using density functional theory modeling, justifying the experimental observations.

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.

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.

Personality is reflected in the brain's intrinsic functional architecture.

Personality describes persistent human behavioral responses to broad classes of environmental stimuli. Investigating how personality traits are reflected in the brain's functional architecture is challenging, in part due to the difficulty of designing appropriate task probes. Resting-state functional connectivity (RSFC) can detect intrinsic activation patterns without relying on any specific task. Here we use RSFC to investigate the neural correlates of the five-factor personality domains. Based on seed regions placed within two cognitive and affective 'hubs' in the brain--the anterior cingulate and precuneus--each domain of personality predicted RSFC with a unique pattern of brain regions. These patterns corresponded with functional subdivisions responsible for cognitive and affective processing such as motivation, empathy and future-oriented thinking. Neuroticism and Extraversion, the two most widely studied of the five constructs, predicted connectivity between seed regions and the dorsomedial prefrontal cortex and lateral paralimbic regions, respectively. These areas are associated with emotional regulation, self-evaluation and reward, consistent with the trait qualities. Personality traits were mostly associated with functional connections that were inconsistently present across participants. This suggests that although a fundamental, core functional architecture is preserved across individuals, variable connections outside of that core encompass the inter-individual differences in personality that motivate diverse responses.