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Aryldiazonium cation undergoes C–C coupling reactions through instant formation of PdIV aryldiazenido complex with the precursor [(Tp*)PdIIMe2]- complex (Tp* = tris(3,5-dimethyl-1-pyrazolyl)borate). This PdIV arylazenido complex is the first high-valent PdIV complex in C–C coupling reactions which can decompose further into aryldiazonium cation and PdII complex and follow a series of reactions via a two-electron or ionic path. Alternatively, it can decompose into aryl radical (AniR) and follow one-electron or radical path forming the C–C coupled product. The possibility of these two mechanisms were proposed by Fekl and co-workers [Dalton Trans. 2017, 46, 4004–4008] and in this work, DFT calculations have been performed to clarify the mechanism as well as to probe the competitive role of aryldiazonium cation and aryl radical (AniR) in this reaction. In the two-electron pathway the process follows sequentially oxidative addition, transmetallation, oxidative addition and dinitrogen extrusion, and reductive elimination to form the C–C coupled product 4,4′-dimethoxybiphenyl (P1) and 4-methoxy toluene (P3). In the one-electron or radical pathway, 4-methoxyphenyl radicals are formed directly and they recombine to give P1. There are other products including [(Tp*)PdIVMe3] (P2) and ethane (P4) formed in the reaction. QTAIM calculations reveal that methyl group migrates as a cation in the transmetallation step of the two-electron path. N2 extrusion passes through a six membered cyclic transition state involving orbital and CH--.π interactions, and reductive elimination passes through a three-membered cyclic transition state. NBO calculations explain the nature of metal-ligand bonding of the species involved in the reaction path. A close inspection of the activation barriers shows the one-electron pathway seems to be favoured over two-electron path because it is low lying and everything becomes irreversible once aryl radical is formed, which quickly undergoes completely irreversible coupling, whereas the first several steps of the two-electron pathway are all reversible. This is in agreement with the experiment and calculations further clarify that the proposed PdIV diaryldiazenido complex is not feasible. Computations thus reveal that aryldiazonium cation starts the reaction by forming [(Tp*)PdIVMe2(pmbd)](RC) complex and this complex reacts favourably through aryl radical to form the products. Aryldiazonium cation readily reacts with the precursor PdII complex to give PdIV aryldiazenido complex and this complex undergoes C–C coupling reaction via radical pathway through aryl radical and forms 4, 4′-dimethoxybiphenyl as a major product, and ethane and 4-methoxytoluene as minor products following PdII/PdIV catalytic cycle. [ABSTRACT FROM AUTHOR]

The influence of phenols upon the fluorescence quenching of 9-aminoacridine (9-AA) was examined in acetonitrile solution by employing steady state and time-resolved fluorescence measurements. On increasing the concentration of quencher molecules the absorption spectra of 9-AA change with significant bathochromic shift. The fluorescence intensity of 9-AA change in presence of quencher molecules were measured at various temperatures as a function of the quencher concentrations. The observed bimolecular quenching rate constant (kq) depends on the nature and electronic effect of substituent present in the quencher molecules. The bimolecular quenching rate constant (kq) decreases on increasing the oxidation potential of quencher molecules. To examine the quenching behavior, kq values were correlated with the free energy change (ΔG). To get forthcoming in the quenching process, fluorescence quenching experiments were carried out in different solvents of varying polarities. The observed result suggest the involvement of charge-transfer quenching mechanism. Lifetime measurements support static quenching. Further, the radical scavenging potential is calculated from density functional theory (DFT) calculations to address the quenching behavior of the quencher molecules. DFT result reveals that electronic features are important in tuning the quenching ability of the quencher molecules and found to agree with the obtained experiment result. [ABSTRACT FROM AUTHOR]

The stereochemical course of the deamination of cis‐2,3‐dimethylaziridine by nitrosyl chloride was investigated at the QCISD/6‐31G(d) level. Calculations reveal that the reaction takes place in two steps. In the first step, the reactants form a pre‐reactive complex, followed by a spiro‐type bicyclic transition state, which on dissociative cycloelimination gives the N‐nitrosoaziridine intermediate. In the second step, this intermediate undergoes cycloreversion through a slightly asynchronous concerted transition state to form an alkene with the same stereochemistry, which is in total agreement with experiment. In the whole reaction, the denitrosation step is found to be rate‐determining. For comparison, geometry optimizations and energies were also obtained at the B3LYP/6‐31G(d) level. It was found that the B3LYP energy results differed significantly from the QCISD ones. To analyze the reason for this difference, B3LYP calculations were repeated by varying the contribution of exact exchange in the Becke functional. With respect to the QCISD results, it has been shown that the functional with 0% exact exchange yields the best activation barriers, whereas the functional with 30% exact exchange is the most suitable one to carry out the complexation and reaction energy calculations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [ABSTRACT FROM AUTHOR]

[Display omitted] • Binuclear zinc complex. • Crystal structure. • Tetrahedral geometry. • Square pyramidal geometry. • Theoretical studies. A new dinuclear zinc coordination complex with di(μ-alkoxido) bridge obtained from [[H 2 L = N,N-(salicyaldene)-1,3-diaminopropan-2-ol] was investigated by IR, 1H- &13C NMR spectroscopy. Single crystal X-ray analysis reveals that the Zn1 atom in the title complex is five coordinated and bound to two alkoxide atoms, two nitrogen atoms, and a chloride ion at apical position in distorted square pyramid geometry, while the second central cation, Zn2, is four coordinated and its O2Cl2 coordination environment is distorted tetrahedral. The single-crystal X-ray crystallographic measurements and DFT calculations reveal that the complex has a bowl-like structure. Hirschfeld surface analysis, energy frameworks QTAIM, NBO, and EDA analyses show clearly that the structure contains a variety of classical and non-classical interactions that help to extend the crystal net dimension. TGA is used to investigate the stability of the structure of the title complex. [ABSTRACT FROM AUTHOR]

Abstract: Hydrolysis of carbonyl dichloride or phosgene (Cl2CO) in gas phase has been investigated at Hartree–Fock, density functional and ab initio levels of theory. The effects of basis sets on the energetics of the reaction have also been explored. Calculations reveal that initially carbonyl dichloride and water form a weak complex and this complex can react further in two ways. In Path 1, water adds on to carbonyl dichloride across carbonyl bond in a concerted fashion to give dichloromethane diol, and this diol decomposes to form chloro formic acid by syn-1,2-elimination of HCl and forms CO2 and HCl as final products. Path 2 is the concerted addition of water across carbon chlorine bond and elimination of HCl in a single step leading to the formation of chloro formic acid directly. This second path that skips the formation of dichloromethane diol is observed to be very low lying and hence is kinetically favored. Addition of second water molecule to the reacting system is found to catalyze the reaction by stabilizing the complex, intermediate and transition states and reduces the activation energy to 24.6kcalmol−1 compared to 29.9kcalmol−1 for a single water molecule. [Copyright &y& Elsevier]