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The structural evolution pathways leading to the conversion of some α-chlorinated carboxylic acids (Cl n H 3-n CCOOH, n = 0, 1, 2, 3) to their respective acid chlorides by thionyl chloride are investigated via density functional theoretical (DFT) modelling. For all compounds where n = 0–3, acid chloride formation occurs via two competing pathways, consisting of three activation barriers in both cases, all of which are enthalpy-controlled and moderate (ΔGǂ < 190 kJ mol−1). Though both pathways are not limited by the same step, they are both composed of only cyclic activated complexes. Rapid intra-molecular small molecule transfer (HCl) allows one pathway to be slight more productive than the other. Whereas all acids evolve via both competing pathways, the evolution of formic acid occurs exclusively via that which involves intramolecular HCl transfer where all the constituent transition states are formed quasi-synchronously. Results for both pathways are summarized in a detail kinetic model which, of-course, is based on the thermodynamic profiles. [Display omitted] • Chlorination of α-chlorinated carboxylic acids proceed via two competing pathways of near equal probabilities. • Chlorination of carboxylic acids occurs fastest via two-step process. • The chlorination rates for carboxylic acids are controlled by a combination steric and electronic factors. • All activated complexes in the transformation if carboxylic acids to acids chlorides are cyclic. • The mechanistic steps for the conversion of carboxylic acids to acid chlorides are enthalpy controlled. [ABSTRACT FROM AUTHOR]

• Two Co(II)-pincer ligands of coorcination modes κ3-SNS and κ3-ONS are reported. • The crystal structure of the pincer ligand pcta is reported. • Both complexes of Co(II) displayed electro-catalytic hydrogen evolution (HER). • The addition of co-ligands bpy or PPh 3 had varying effects on the HER. Bis- N -(2,5-dimethoxyphenyl)pyridine-2,6-dicarbothioamide (pdcta) and N -(2,5- dimethoxyphenyl)-6-[(2,5-dimethoxyphenyl)carbamothioyl]pyridine-2-carboxamide (pcta) were synthesized from a one pot mixture as pincer ligands. Crystals of pcta , grown from CDCl 3 were structurally characterized, and found to crystallize in the space group P 2 1 / c. The Co(II) complexes [Co(II)(κ3-SNS-pdcta)(CH 3 CO 2)(H 2 O)] (1) and [Co(II)(κ3-ONS-pcta)(CH 3 CO 2)(H 2 O)]·H 2 O (2) were prepared from the reaction of pdcta and pcta and Co(CH 3 CO 2) 2 ·4H 2 O in ethanol at reflux under argon atmosphere. The identities of 1 and 2 were confirmed from their elemental analyses, ESI MS and a series of spectroscopic measurements. Both complexes displayed electrocatalytic hydrogen evolution with p -toluene sulfonic acid monohydrate in the presence and absence of bpy or PPh 3 co-ligands. The hydrogen evolution occurred at moderate overpotentials (605–780) mV, with 1 giving better Faradaic efficiencies than 2 under all the conditions explored herein. Thermodynamic estimates, based on the reduction potentials, suggest that the homolytic pathway for the production of hydrogen from the CoIII-hydride species generated in the presence of the proton source, is more favourable than the heterolytic pathway in CH 3 CN. [ABSTRACT FROM AUTHOR]

Abstract: The reaction between ZnCl2 and di-2-pyridyl ketone benzoyl hydrazone (dpkbh) in acetonitrile under ultrasonic or reflux conditions gave [ZnCl2(η3-N,N,O-dpkbh)] in good yield. The identity of the compound was established from the results of its elemental analysis and a number of spectroscopic measurements. Solid-state infrared spectra of [ZnCl2(η3-N,N,O-dpkbh)] reveal the coordination of dpkbh, the presence of the amide proton and binding of the oxygen atom of dpkbh. 1H NMR spectra of [ZnCl2(η3-N,N,O-dpkbh)] show sensitivity to solvent and temperature variations and confirm the coordination of dpkbh. The electronic absorption spectra of [ZnCl2(η3-N,N,O-dpkbh)] in non-aqueous media show high sensitivity to changes in their surroundings and divulge two interlocked intra-ligand-charge transfer (ILCT) transitions of the donor–acceptor type between 300 and 500nm. Optical measurements show reversible inter-conversion between two forms of [ZnCl2(η3-N,N,O-dpkbh)] that may be due to complex–substrate interactions and thermodynamic analysis gave changes in enthalpy (ΔH θ ) of −23.3 and +14.1kJmol−1, entropy (ΔS θ ) of −51 and +31Jmol−1K−1, and free energy (ΔG θ ) of −8.16 and +4.54kJmol−1 at 298.15K in DMF and DMSO, respectively. Substrates in concentrations as low as 10−5 M can be detected and determined using [ZnCl2(η3-N,N,O-dpkbh)] in polar solvents. A provisional model for the binding of substrate to [ZnCl2(η3-N,N,O-dpkbh)] is developed and a binding constant in the range 6000–8000M−1 is obtained in the case of ZnCl2 in DMSO. Electrochemical measurements on [ZnCl2(η3-N,N,O-dpkbh)] in DMF show irreversible metal and ligand-based redox processes, and electrochemical reactions of dpkbh with ZnCl2 show facile coordination of ZnCl2 and formation of [ZnCl2(η3-N,N,O-dpkbh)]. X-ray structural analysis done on a crystal grown from a DMF solution of [ZnCl2(η3-N,N,O-dpkbh)] confirmed the identity of [ZnCl2(η3-N,N,O-dpkbh)] and shows an extensive network of non-covalent interactions that connects all molecules. [Copyright &y& Elsevier]