Experimental Evidence for Zerovalent Pd(NHC) as a Competent Catalyst in C-N Cross-Coupling (NHC = DiMeIHeptCl).

Use of the branched N-heterocyclic carbene (NHC) ligand 1,3-bis(2,6-bis(3-methyl-1-(2-methylpropyl)butyl)phenyl)-4,5-dichloro-1,3-dihydro-2H-imidazole-2-ylidene (DiMeIHeptCl) facilitated the stabilization of several relevant intermediates for Pd(NHC)-catalyzed C-N cross-coupling reactions. Complexes [Pd(DiMeIHeptCl)]2(µ-N2), [Pd(DiMeIHeptCl)]2(µ-η2-1,2-η2-4,5-C6H6), and Pd(DiMeIHeptCl)(pyridine), representing zerovalent Pd(NHC) bearing labile ligands, were isolated and structurally characterized, along with divalent PdCl(Ph)(DiMeIHeptCl) and PdCl(Ph)(DiMeIHeptCl)(n-propylamine). The former is a 14-electron Pd complex, which is stable under air and chromatography on silica gel or neutral alumina. One possible reason for this exceptional stability is the numerous dispersion interactions between the NHC alkyl chains and the Pd-Ph group. Detailed investigations of catalyst activation and oxidative addition confirmed that "Pd(NHC)" is formed from many known Pd(II)(NHC) precatalysts and provided activation rates for these different precatalysts.

Optical and computational study of the trans ↔ cis reversible isomerization of the commercial bis-azo dye Bismarck Brown Y.

The trans-cis-trans isomerization behaviour of Bismarck Brown Y (BBY) during and after irradiation with visible light, was characterized in detail for the first time by means of optical pump-probe experiments, to study the geometric inter-conversion of bis-azobenzene both in solution and embedded in multi-layered polymeric thin films. The rate constants observed for the thermal cis-trans back isomerization permit a determination of how the thermal isomerization is influenced by its local environment. In both solution and when incorporated into multi-layered thin films, the thermal relaxation observed for the commercial azo dye BBY showed a highly unusual biexponential decay, which clearly demonstrates two distinct isomerization processes. The cis decay showed an anomalous fast isomerization process on the timescale of milliseconds, followed by a slower isomerization process with a cis lifetime on the order of seconds. It was further observed that the faster isomerization process was influenced more by its local environment than was the slower process. The faster isomerization process also displayed a higher rate constant in aprotic solvents such as THF and DMF compared to that observed in protic solvents such as ethanol and water. Additionally, a higher rate constant was observed in solution compared to the multi-layered thin films where motion of the azo molecules was likely more restricted. Following recrystallization of the BBY azo dye, the more expected monoexponential decay was observed for the cis isomer in solution, with a single cis lifetime calculated on the timescale of seconds. This timescale corresponded well to values predicted by density functional theory calculations.

Ligand Electrochemical Parameter Approach to Molecular Design. σ-Donation, π-Back Donation, and Other Metrics in Ruthenium(II) Dinitrogen Complexes.

Using the density functional theory, [(N2)RuIIL5]n+ species are studied in silico. The properties of the Ru-N2 bond are derived, including σ-donation, π-back donation, Ru-N and N-N bond lengths and bond orders, net charges and NN stretching frequencies, and so forth. These data are correlated using the ligand electrochemical parameter (EL) theory, whereby the availability of electrons in the [RuL5]n+ fragment is defined by its electron richness, which is the sum of the EL parameters, ΣEL(L5). The objective is to better understand the binding of the N2 ligand, leading to a molecular design whereby a specific species is constructed to have a desired property, for example, a particular bond length or charge. We supply cubic expressions linking ΣEL(L5) with these many metrics, allowing researchers to predict metric values of their own systems. The extended charge decomposition analysis is used. For the given target, N2, σ-bonding does not vary greatly with the nature of ligand L, and π-back donation is the dominant property deciding the magnitudes of the various metrics. The EL parameter provides the path to design the desired species. This contribution is devoted to dinitrogen, but the method is expected to be general for any ligand, including polydentate ligands.

Modeling ligand electrochemical parameters by repulsion-corrected eigenvalues.

Ligand electrochemical parameters, EL , more commonly known as Lever parameters, have played a major research role in understanding redox processes involved in inorganic electrochemistry, enzymatic reactions, catalysis, solar cells, biochemistry, and materials science. Despite their broad usefulness, Lever parameters are not well understood at a first-principles level. Using density functional theory, we demonstrate in this contribution that a ligand's Lever parameter is fundamentally related to the ligand's ability to alter the eigenvalue of the electroactive spin-orbital in an octahedral transition metal complex. Our analysis furthers a first-principles understanding of the nature of Lever parameters.

(DiMeIHeptCl)Pd: A Low-Load Catalyst for Solvent-Free (Melt) Amination.

(DiMeIHeptCl)Pd, a hyper-branched N-aryl Pd NHC catalyst, has been shown to be efficient at performing amine arylation reactions in solvent-free ("melt") conditions. The highly lipophilic environment of the alkyl chains flanking the Pd center serves as lubricant to allow the complex to navigate through the paste-like environment of these mixtures. The protocol can be used on a multi-gram scale to make a variety of aniline derivatives, including substrates containing alcohol moieties.

A SiPM-Enabled Portable Delayed Fluorescence Photon Counting Device: Climatic Plant Stress Biosensing.

A portable and sensitive time-resolved biosensor for capturing very low intensity light emission is a promising avenue to study plant delayed fluorescence. These weak emissions provide insight on plant health and can be useful in plant science as well as in the development of accurate feedback indicators for plant growth and yield in applications of agricultural crop cultivation. A field-based delayed fluorescence device is also desirable to enable monitoring of plant stress response to climate change. Among basic techniques for the detection of rapidly fluctuating low intensity light is photon counting. Despite its vast utility, photon counting techniques often relying on photomultiplier tube (PMT) technology, having restricted use in agricultural and environment measurements of plant stress outside of the laboratory setting, mainly due to the prohibitive cost of the equipment, high voltage nature, and the complexity of its operation. However, recent development of the new generation solid-state silicon photomultiplier (SiPM) single photon avalanche diode array has enabled the availability of high quantum efficiency, easy-to-operate, compact, photon counting systems which are not constrained to sophisticated laboratories, and are accessible owing to their low-cost. In this contribution, we have conceived, fabricated and validated a novel SiPM-based photon counting device with integrated plug-and-play excitation LED, all housed inside a miniaturized sample chamber to record weak delayed fluorescence lifetime response from plant leaves subjected to varying temperature condition and drought stress. Findings from our device show that delayed fluorescence reports on the inactivation to the plant's photosystem II function in response to unfavorable acute environmental heat and cold shock stress as well as chronic water deprivation. Results from our proof-of-concept miniaturized prototype demonstrate a new, simple and effective photon counting instrument is achieved, one which can be deployed in-field to rapidly and minimally invasively assess plant physiological growth and health based on rapid, ultra-weak delayed fluorescence measurements directly from a plant leaf.

Electrochemical Parametrization in Sandwich Complexes of the First Row Transition Metals.

Applying the ligand electrochemical parameter approach to sandwich complexes and standardizing to the Fe(III)/Fe(II) couple, we obtained E(L)(L) values for over 200 pi-ligands. Linear correlations exist between formal potential (E degrees ) and the summation operatorE(L)(L) for each metal couple. In this fashion, we report correlation data for many first row transition metal couples. The correlations between the E(L)(L) of the substituted pi-ligand and the Hammett substituent constants (sigma(p)) are also explored.

Biodegradable open cell foams of telechelic poly(epsilon-caprolactone) macroligand with ruthenium (II) chromophoric subunits via sub-critical CO2 processing.

This work reports on the effect of CO2 at subcritical conditions and the gaseous state on the telechelic poly(epsilon-caprolactone) polymers. The tested polymers are semi-crystalline in nature and thus the effect of functional groups and their overall contribution to foaming and formation of microstructures with open-cell morphollogy is discussed.

Electronic structure and spectra of linkage isomers of bis(bipyridine)(1,2-dihydroxy-9,10-anthraquinonato)ruthenium(ii) and their redox series.

Linkage isomers of bis(bipyridine)(1,2-dihydroxy-9,10-anthraquinonato)ruthenium(II), 1,2- and 1,9-coordinated complexes, and several of their oxidation products have been prepared chemically and/or electrochemically. For the 1,2-coordinated complex, the one- and two-electron oxidized species have been characterized, and for the 1,9-coordinated complex, the one-electron oxidized species has been characterized. The rich redox activity of these complexes leads to ambiguity in assessing the electronic structure. This paper reports EPR spectra of odd-electron species and detailed analyses of electronic spectra and structure of the complexes, based on INDO molecular orbital calculations. Results of calculations on the related 1-hydroxyanthraquinone complex and the free ligands,1,2-dihydroxy-9,10-anthraquinone (alizarin) and 1-hydroxyanthraquinone, are also briefly discussed.