Terpyridine ligands are widely used in chemistry and material sciences owing to their ability to form stable molecular complexes with a large variety of metal ions. In that context, variations of the substituents on the terpyridine ligand allow modulation of the material properties. Applying the Stille cross-coupling reaction, we prepared with good yields a new series of terpyridine ligands possessing quinoline-type moieties in ortho, meta, and para positions and dimethylamino substituents at central or distal positions. The corresponding cobalt(II) complexes were synthesized and fully characterized by elemental analysis, single-crystal X-ray crystallography, mass spectrometry, and UV-vis, H NMR, and Fourier transform infrared (FT-IR) spectroscopy as well as by cyclic voltammetry (CV). Density functional theory (DFT) calculations were performed to investigate the electronic structure of all the Co(II) bis-terpyridyl molecular complexes. In this work, we show that terpyridine ligand functionalization allows tuning the redox potentials of the Co(III)/Co(II), Co(II)/Co(I), and Co(I)/Co(I) (tpy) couples over a 1 V range.

Starting from an easily available pyridinol derivative, a route to penta(2-thienyl)pyridine and related symmetrical compounds is reported. Key reactions are activation of the pyridine core and metal-catalyzed couplings proving the efficacy of these methods even in sterically highly encumbered systems. UV/vis and fluorescence spectra as well as first cyclovoltametric measurements of the synthesized novel thiophene-pyridine conjugates are reported.

Preparation of as eries of terpyridyl ligandsb earing different substituents recently led to the synthesis of new cobalt-bisterpyridyl complexes spanning over aw ide range of redox potentials. In this work, we describet he catalytic properties of these complexes for the electroreduction of protons into hydrogen (hydrogen evolution reaction( HER)) in acetonitrile. The substituents of the ligands were found to greatly affect the catalytic performances of the systems, in terms of stability and overpotential. Interestingly,s ystemsb ased on dimethylaminoterpyridine derivatives perform HER with highe fficiency,l ow overpotential and excellent stability. Density functional theory calculations were used to providei nsights into the reaction mechanism of HER catalyzed by these systems, highlighting the role of the ligand for protonactivation.Major efforts are currently employed into the development of green energy technologies based on solar and wind power. However,t hese energy sourcess uffer from low energetic density and intermittency.T oo vercome such failings, ac ommon approachi nvolves storage of the generatede nergy by conversion into chemical energy through the formation of chemical bonds. The best examples of these strategies are the photochemicalo re lectrochemical reduction of protons (2H + )t om olecular hydrogen (H 2 ), allowing energy storagethrough the formation of an HÀHc hemical bond. [1][2][3] The kinetic barrierf or such at ransformation is large, hence,c atalysts are required to lower it.Although metallic platinum remains the most effective catalytic materialf or the hydrogen evolution reaction( HER), its limited availability and high cost justifiest he quest for alternative catalysts based on cheaper and more abundant non-noble metals.C urrent research focuses primarily on two types of compounds:h eterogeneousm aterials and homogeneous metal complexes. Despite being more complex than heterogeneous materials, molecular catalysts are often ideal for fine tuning reactivity through syntheticm odificationso f the ligands. In this context,significant successhas been recently obtained with molecular cobalt complexes,i np articular cobaloximes, cobalt-diimine-dioximes andc obalt-polypyridine complexes. [3][4][5][6][7] The latter possess remarkablea bility to store multiple reducing equivalents, as the ligand not only stabilizes the reduced metal centerb ut also accumulates electrons within its p-conjugated system. Within this class of compounds, our group hasi nvestigated the rarely studied potential of simple and cheap cobalt-bisterpyridine complexes as catalysts for CO 2 and proton reduction. [8] We have shown that these complexes can be graftedo nt he surface of glassy carbon electrodes, on which they display significant HER activity. [9] To optimize such catalysts, we have synthesized av ariety of new terpyridines with different substituents (very few functionalized terpyridine derivatives were commercially available). Synthesis and characterization of the corresponding cobalt complexes (C1-C8 in Figure ...

The combination of 2,2':6',2''-terpyridines (tpy) and Ru II is knownt od eliverm olecular and supramolecular assembliesw ith remarkablep roperties.H ere new Ru II complexes, with modified tpy ligandss ubstituted with varying numbers of dimethlyamino groups,a re presented. Electrochemistry shows that the incorporation of the strongly electron-donatingg roups on the tpy ligands leads to an egative shift of the Ru II oxidation potentialb yc lose to 1V .T he reductive electrochemical responses are strongly dependent on the nature of the working electrode, with glassyc arbon and gold working electrodes showing the best results. These observations led to the development of am odified Optically Transparent Thin Layer Electrochemical (OTTLE)c ell, based on ag old working electrode. The use of UV/Vis/NIR spectroelectrochemical methods with that OTTLE cell, together with simulations of the cyclic voltammograms, allowed the characterization of four reduction steps in these complexes, the final two of which lead to bond activationsa tt he ruthenium center.T his observation is to the best of our knowledge unprecedented in coordinatively saturated complexes of type [Ru (tpy) 2 ] 2 + .T he variousr edox states of the complexes were characterized by EPR spectroelectrochemistry and through DFT calculations. The results presented here establish these substitutedt py ligands as highly attractive ligands in coordination chemistry,a nd displayt he utility of ag old-basedO TTLE cell for spectroelectrochemicalm easurements.

A three-component reaction with lithiated alkoxyallenes, nitriles, and perfluorinated carboxylic acids as precursors led to a series of perfluoroalkyl- or perfluoroaryl-substituted 4-hydroxypyridine derivatives. These compounds were converted into 4-pyridyl nonaflates which can be employed as versatile building blocks for the synthesis of pi-conjugated compounds with use of palladium-catalyzed couplings. Suzuki reactions at C-4 and C-3 of the pyridine ring proceeded with moderate to high yields. In addition, Suzuki-Miyaura, Stille, or Buchwald-Hartwig coupling reactions have also been studied and afforded the corresponding highly substituted pyridine derivatives. Starting from an arylated propargylic ether the three-component reaction led to a pentasubstituted 4-hydroxypyridine derivative that could also be employed in palladium-catalyzed processes at C-4 and at C-3 of the pyridine core. With this simple approach the sterically highly crowded 3,4,5-triphenyl-substituted pyridine derivative 37a could be prepared and studied by an X-ray analysis. With acetonitrile as precursor a different reaction pathway was found when this component was used in excess resulting in a pyridine derivative with a new substitution pattern. In summary, the methods described here allow a flexible and fairly efficient entry to a variety of highly substituted pyridine derivatives bearing perfluorinated alkyl or aryl groups.