Erratum to: Axial Imidazole Binding Strengths in Porphyrinoid Cobalt(III) Complexes as Studied by Tandem Mass Spectrometry

The Co(II) complexes of twelve meso-tetraaryl-porphyrins, -chlorins, and chlorin analogues containing non-pyrrolic heterocycles were synthesized and converted in situ to the corresponding Co(III) complexes coordinated to one or two imidazoles. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) in conjunction with the energy-variable collision-induced dissociation (CID) technique was used to compare the relative gas-phase binding strength of the axially coordinated imidazoles to the octahedral and square planar Co(III) porphyrinoid complex ions. The observed binding energies of these ligands were rationalized in terms of the effects of porphyrinoid core structure and meso-substitution on the electron density on the central Co(III) centers. Some of these trends were supported by DFT-based computational studies. The study highlights to which extend porphyrins vary from chlorins and chlorin analogues in their coordination abilities and to which extraordinary degree meso-thienyl-substituents influence the electronic structure of porphyrins. The study also defines further the scope and limits CID experiments can be used to interrogate the electronic structures of metalloporphyrin complexes.     

Divalent NI Compounds: Identifying new Carbocyclic Carbenes to Design Nitreones using Quantum Chemical Methods

Nitreones are compounds with oxidation state 1 at the nitrogen, these compounds carry formal positive charge as well as two lone pairs of electrons at nitrogen center. These compounds are also known as divalent N^I compounds and can be represented with the general formula L → N⁺ ← L, where L is an electron donating ligand. In the recent past, several divalent N^I compounds have been reported with L = N-heterocyclic carbene (NHC), remote N-heterocyclic carbene (rNHC), carbocyclic carbene (CCC) and diaminocarbene. Recently, our group reported that a novel six-membered CCC (cyclohexa-2,5-diene-4-[diaminomethynyl]-1-ylidene) can stabilize N⁺ center in nitreones. As an independent carbene, this species is very unstable. In this work, modulation of this CCC using (a) annulation, (b) heterocyclic ring modification, (c) substitutions adjacent to the carbenic carbon, (d) exocyclic double bond insertion and (e) ring contraction, has been reported. These modulations and quantum chemical analyses helped in the identification of five new six-membered CCCs which carry improved donation and stability properties. Further, these CCCs were employed in the design of new divalent N^I compounds (nitreones) which carry coordination bonds between ligands and N⁺ center. The molecular and electronic structure properties, and the donor→acceptor coordination interactions present in the resultant low oxidation state divalent N^I compounds have been explored.     

Hydrocarbon group type analysis of petroleum heavy fractions using the TLC-FID technique

Hydrocarbon group type analysis is important in all conversion processes and in preparation of feed for these conversion processes so as to learn the selectivity of the different type of catalysts for product yield and quality. The use of the Mark 5 Iatroscan detector and the method reported here allowed for a rapid and quantitative hydrocarbon group type analysis of petroleum residues without prior separation of asphaltenes. SARA type analyses of petroleum residues have been performed by a three stage development using n-hexane, toluene and DCM (95%):MeOH (5%). The standard deviation and coefficient of variation in repeated measurements by this method were as low as 0.65 wt% or less and 3.5 wt% or less, respectively. The time required for analysis of 10 samples could be as short as 90 min. Received: 20 May 1997 / Revised: 12 August 1997 / Accepted: 16 August 1997     

Catalysis and mechanistic studies of ruthenium and osmium on synthesis of anthranilic acids

Ruthenium, osmium and ruthenium + osmium catalyzed synthetic methodology was developed for the synthesis of anthranilic acids from indoles in good to excellent yields using bromamine‐B in alkaline acetonitrile–water (1:1) at 313 K. Detailed catalysis studies of ruthenium, osmium and the mixture of both were carried out for the synthetic reactions. The positive synergistic catalytic activity of Ru(III) + Os(VIII) was observed to a large extent with the activity greater than the sum of their separate catalytic activities. Detailed kinetic and mechanistic investigations for each catalyzed reactions were carried out. The kinetic pattern and mechanistic picture of each catalyzed reaction were found to be different for each catalyst and to obey the underlying rate laws: where, x, y < 1. The reactions were studied at different temperatures and the activation parameters were evaluated for each catalyzed reaction. Under the identical set of experimental conditions, the kinetics of all the three catalyzed reactions were compared with uncatalyzed reactions, revealing that the catalyzed reactions were 6‐ to 42‐fold faster. The catalytic efficiency of aforementioned catalysts followed the order: Ru(III) + Os(VIII) > Os(VIII) > Ru(III). This trend may be attributed to the different d‐electronic configuration of the catalysts. The proposed mechanisms and the rigorous kinetic models derived give results that fit well with the experimental data in each catalyzed reaction. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient protocol for the synthesis of quinoxaline, benzoxazole and benzimidazole derivatives using glycerol as green solvent

A straightforward, efficient and more sustainable catalyst-free method has been developed for the synthesis of quinoxaline, benzoxazole, and benzimidazole ring system in glycerol to achieve yields that were comparable to or better than, those in conventional media. It is noteworthy that the reaction was exclusively carried out in glycerol-water system, rendering the methodology highly valuable from both environment and economic points of view.     

Unusual Nitrene Oxidation Product Formation by Metathesis Involving the Dioxygen O−O and Borylnitrene B−N Bonds

The reaction of dioxygen with nitrenes can have significant energy barriers, although both reactants are triplet diradicals and the formation of nitroso-O-oxides is spin-allowed. By means of matrix-isolation infrared spectroscopy in solid argon, nitrogen, and neon, and through high-level computational quantum chemistry, it is shown herein that a 3-nitreno-1,3,2-benzodioxaborole CatBN (Cat=catecholato) reacts with dioxygen under cryogenic conditions thermally at temperatures as low as 7 K to produce two distinct products, an anti-nitroso-O-oxide and a nitritoborane CatBONO. The computed barriers for the formation of nitroso-O-oxide isomers are very low. Whereas anti-nitroso-O-oxide is kinetically trapped, its bisected isomer has a very low barrier for metathesis, yielding the CatBO+NO radicals in a strongly exothermic reaction; these radicals can combine under matrix-isolation conditions to give nitritoborane CatBONO. The trapped isomer, anti-nitroso-O-oxide, can form the nitritoborane CatBONO only after photoexcitation, possibly involving isomerization to the bisected isomer of anti-nitroso-O-oxide.     

Catalytic Oxidation of Alcohols and Amines to Value‐Added Chemicals using Water as the Solvent

Designing reactions in aqueous media has been one of the major challenges in modern organic synthesis, especially to avoid the use of large amounts of organic solvents whose disposal is a matter of grave concern from an environmental perspective. The oxidation of alcohols and amines is an essential and important step in the synthesis of many valuable products including polymers and pharmaceuticals. In recent times, there has been a surge in the use of water as a solvent in many organic reactions. This review focuses specifically on the oxidation reactions of alcohols and amines carried out in water media using transition metal catalysts, metal‐free catalysts and photocatalysts.     

Iron(III)–salen complex on a polymer scaffold as heterogeneous catalyst for synthesis of benzimidazoles

Research on Chemical Intermediates - Benzimidazoles are important bioactive compounds with diverse applications in the medicinal, industrial, as well as agrochemical fields. In this study, an...     

A novel imidazolium‐supported palladium–chloroglycine complex: copper‐ and solvent‐free high‐turnover catalysts for the Sonogashira coupling reaction

A novel, effective 1‐glycyl‐3‐methyl imidazolium chloride–palladium(II) complex ([Gmim]Cl–Pd(II)) was synthesized and studied as an organocatalyst for the Sonogashira coupling reaction under solvent‐free conditions at 25 °C. The hydrophobic group on amino acid favors reagent diffusion toward the chloroglycine moiety, increasing the catalytic activity of supported palladium complex. By this protocol, different aryl halides (Cl, Br and I) were reacted with phenylacetylene in good to excellent yields with turnover number 8.0 × 10² to 9.6 × 10². The catalyst was recycled for the reaction of bromobenzene with phenylacetylene for eight runs without appreciable loss of its catalytic activity and negligible metal leaching. Copyright © 2012 John Wiley & Sons, Ltd.