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[Co(dmgBF2)2(H2O)2] 1 (where dmgBF2 = difluoroboryldimethylglyoximato) was used to synthesize [Co(dmgBF2)2(H2O)(py)]·0.5(CH3)2CO 2 (where py = pyridine) in acetone. The formulation of complex 2 was confirmed by elemental analysis, high resolution MS, and various spectroscopic techniques. The complex [Co(dmgBF2)2(solv)(py)] (where solv = solvent) was readily formed in situ upon the addition of pyridine to complex 1. A spectrophotometric titration involving complex 1 and pyridine proved the formation of such a species, with formation constants, log K = 5.5, 5.1, 5.0, 4.4, and 3.1 in 2-butanone, dichloromethane, acetone, 1,2-difluorobenzene/acetone (4 : 1, v/v), and acetonitrile, respectively, at 20 °C. In strongly coordinating solvents, such as acetonitrile, the lower magnitude of K along with cyclic voltammetry, NMR, and UV-visible spectroscopic measurements indicated extensive dissociation of the axial pyridine. In strongly coordinating solvents, [Co(dmgBF2)2(solv)(py)] can only be distinguished from [Co(dmgBF2)2(solv)2] upon addition of an excess of pyridine, however, in weakly coordinating solvents the distinctions were apparent without the need for excess pyridine. The coordination of pyridine to the cobalt(II) centre diminished the peak current at the Epc value of the CoI/0 redox couple, which was indicative of the relative position of the reaction equilibrium. Herein we report the first experimental and theoretical 59Co NMR spectroscopic data for the formation of Co(I) species of reduced cobaloximes in the presence and absence of py (and its derivatives) in CD3CN. From spectroelectrochemical studies, it was found that pyridine coordination to a cobalt(I) metal centre is more favourable than coordination to a cobalt(II) metal centre as evident by the larger formation constant, log K = 4.6 versus 3.1, respectively, in acetonitrile at 20 °C. The electrosynthesis of hydrogen by complexes 1 and 2 in various solvents demonstrated the dramatic effects of the axial ligand and the solvent on the turnover number of the respective catalyst.

The synthesis and crystal structures of bis-N-(2,5-dimethoxyphenyl)pyridine-2,6-dicarbothioamide (dicarbothioamide I) and 6-(4,7-dimethoxy-2-benzothiazolyl)-N-(2,5-dimethoxyphenyl)-2-pyridinecarbothioamide (L 1 ) as well as the syntheses of the palladium(II) chloride and acetate pincer complexes are reported. The stability constant for the palladium complex formation at 258C was found to be (2.04 AE 0.26) Â 10 4 dm 3 mol À1 and (2.30 AE 0.19) Â 10 4 dm 3 mol À1 with D f H ¼ 8 AE 1 kJ mol À1 , D f S y ¼ 108 AE 10 J K À1 mol À1 , and D f H ¼ 17 AE 4 kJ mol À1 and D f S y ¼ 140 AE 20 J K À1 mol À1 for the PdClL 1 and Pd(OAc)L 1 , respectively. The kinetics of formation of the palladium(II) complexes were investigated and the mechanism is proposed to be associative in nature (DH 1 z ¼ 34 AE 2 kJ mol À1 and DS 1 z ¼ À113 AE 8 J K À1 mol À1 , and DH 1 z ¼ 37 AE 3 kJ mol À1 and DS 1 z ¼ À100 AE 8 J K À1 mol À1 for the PdClL 1 and Pd(OAc)L 1 species, respectively). The electrochemical measurements of the acetonitrile solutions revealed irreversible electron transfers consistent with the electrochemical decomposition of the ligand and its coordination complexes.

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The Co(I) species resulting from the reduction of two mononuclear species [CoL n Cl 2 ] (where L = 2,2'bipyridine (bpy) and n = 2, or L = trans-2-(2'-quiolyl)methylene-3-quinuclidione (quin) and n = 1), was studied by 59 Co NMR spectroscopy, UV-visible-NIR spectroscopy, and spectroelectrochemical techniques. A quasi-stable Co(I) species produced by the reduction of [Co(bpy) 2 Cl 2 ] was studied and gave a 59 Co NMR spectroscopic chemical shift of 2934 ppm in CD 3 CN-D 2 O (4:1, v/v) and a broad peak of  max = 600 nm in the UV-visible region of the spectrum. The Co(I) species generated from [Co(quin)Cl 2) (when reduced by electrochemical methods) was found to be unstable and produced a transient of  max = 530 nm. Both [CoL n Cl 2 ] species were examined as electrocatalysts for the proton reduction in an acetonitrile-water solvent mixture in the presence of p-cyanoanilinium tetrafluoroborate. The electrochemical properties of both species showed a dependence on the supporting electrolyte which also affected the electrocatalytic behavior. The simulation of the cyclic voltammograms in CH 3 CN-H 2 O (4:1, v/v) allowed for the extraction of kinetic data and suggested a homogenous reaction following the reduction to a Co(I) metal centre with rate constants k = 0.01 s-1 and 2 M s-1 for the Co(I) species with the ligands, bpy and quin, respectively. Analysis of the head space of controlled potential electrolysis experiments for an hour, in the presence of p-cyanoanilinium tetrafluoroborate, confirmed the production of hydrogen, and also showed that the supporting electrolyte affected the production of hydrogen at a glassy carbon electrode in CH 3 CN-H 2 O (either 1:1 or 4:1, v/v). A mechanism was postulated which involved a Co III-H species as the most likely candidate and appeared to involve both a homolytic and a heterolytic pathway towards the production of hydrogen.

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