Charles H. Devillers

Aromatic Nucleophilic Substitution (SNAr) of meso-Nitroporphyrin with Azide and Amines as an Alternative Metal Catalyst Free Synthetic Approach To Obtain meso-N-Substituted Porphyrins

Aromatic nucleophilic substitution reaction of the nitro group of meso-nitroporphyrins with azide and various amines was achieved and represents an alternative procedure to C-N coupling reactions usually needed to obtain such meso-N-substituted porphyrins in good yields.

Exploring the redox reactivity of magnesium porphine. Insight into the origins of electropolymerisation

Magnesium(II) porphine, MgP (1), was synthesised according to the Lindsey procedure allowing to isolate and crystallise 1-formyldipyrromethane (2) as a synthetic intermediate. Unprecedented X-ray diffraction studies revealed multiple intermolecular associations in the crystal between neighbouring units of 2, namely hydrogen bonds and CH...pi. The electrochemical behaviour of 1 was examined by means of cyclic voltammetry. In oxidation, two well-defined and distinct steps are assigned to macrocycle concerned electron transfers yielding initially the pi-cation radical and pi-dication, respectively. The highly reactive dication condenses neutral magnesium porphine to form a diprotonated di-isoporphine species, which is assumed to be a key intermediate at the origin of the electropolymerisation. Electrolyses were performed at the potential of the pi-cation radical generation. Investigation of the electrolysed solution by UV-vis spectroscopy and MALDI-TOF spectrometry revealed the presence of several oligoporphyrins, with diporphine as an important product. In all the oligomers series, extensive demetallation is evidenced, due to the increasing acidity of the medium as oligomerisation progresses. This demetallation could be prevented by addition of 2,6-lutidine as a base prior to electrolysis. In the oligomer series, the porphine units seem to be connected through meso-meso bonds, an argument supported by certain features of the UV-vis spectrum. Finally, the mechanism of oxidative oligomerisation is discussed, from the point of view of the initial steps of the electropolymerisation.

Electrosynthesis of Imidazolium Carboxylates

Synthesis of imidazolium carboxylate compounds was efficiently achieved by electrochemical reduction of imidazolium precursors under very mild conditions.

Kinetic and Electrochemical Studies of the Oxidative Addition of Demanding Organic Halides to Pd(0): the Efficiency of Polyphosphane Ligands in Low Palladium Loading Cross-Couplings Decrypted

Oxidative addition (OA) of organic halides to palladium(0) species is a fundamental reaction step which initiates the C-C bond formation catalytic processes typical of Pd(0)/Pd(II) chemistry. The use of structurally congested polyphosphane ligands in palladium-catalyzed C-C bond formation has generated very high turnover numbers (TONs) in topical reactions such as Heck, Suzuki, Sonogashira couplings, and direct sp(2)C-H functionalization. Herein, the OA of aryl bromides to Pd(0) complexes stabilized by ferrocenylpolyphosphane ligands L1 (tetraphosphane), L2 (triphosphane), and L3 (diphosphane) is considered. The investigation of kinetic constants for the addition of Ph-Br to Pd(0) intermediates (generated by electrochemical reduction of Pd(II) complexes coordinated by L1-L3) is reported. Thus, in the OA of halides to the Pd(0) complex coordinated by L1 the series of rate constants kapp is found (mol(-1) L s(-1)): kapp(Ph-Br) = 0.48 > kapp(ClCH2-Cl) = 0.25 ≫ kapp(p-MeC6H4-Br) = 0.08 ≈ kapp(o-MeC6H4-Br) = 0.07 ≫ kapp(Ph-Cl). Kinetic measurements clarify the influence that the presence of four, three, or two phosphorus atoms in the coordination sphere of Pd has on OA. The presence of supplementary phosphorus atoms in L1 and L2 unambiguously stabilizes Pd(0) species and thus slows down the OA of Ph-Br to Pd(0) of about 2 orders of magnitude compared to the diphosphane L3. The electrosynthesis of the complexes resulting from the OA of organic halides to [Pd(0)/L] is easily performed and show the concurrent OA to Pd(0) of the sp(3)C-Cl bond of dichloromethane solvent. The resulting unstable Pd/alkyl complex is characterized by NMR and single crystal X-ray structure. We additionally observed the perfect stereoselectivity of the OA reactions which is induced by the tetraphosphane ligand L1. Altogether, a clearer picture of the general effects of congested polydentate ligands on the OA of organic halides to Pd(0) is given.

Electrosynthesis as a Powerful Method for the Generation of Catalytic Intermediates: Efficient Isolation of a Palladium Aryl Halide Oxidative Addition Product

Electrosynthesis has become a useful and commonly used technique in organic chemistry. Conversely, its use is still limited in organometallic synthesis, despite its potential to control at the finest level, through electron transfer, elementary steps of important metal-mediated transformations. This lack of popularity partly originates in the potential difficulty in separating the reaction products from the supporting electrolyte. Yet, in the vast majority of cases the separation can be readily achieved in many practical ways such as selective precipitation, solid–liquid or liquid–liquid extraction, and even sometimes column chromatography. Electrochemical studies have greatly contributed to the mechanistic understanding of catalytic cross-coupling reactions, for instance by employing valuable analytical methods to investigate features of [(Pd,Pd)/phosphane(s)] active organometallic catalysts. In general, in mechanistic investigations the isolation and characterization of catalytic intermediates is of crucial importance. In this purpose, various chemical methods have been employed, which allow forming model compounds of aryl halides oxidative addition on palladium species stabilized by chelating diphosphanes or several monophosphanes. 7] As illustrated in Scheme 1, both the trans-ligation on preformed [Pd ACHTUNGTRENNUNG(aryl) ACHTUNGTRENNUNG(halide)] complexes and the direct oxidative addition on stabilized [Pd(diphosphane)] precursors are possible. Each of these methods to form [LnPd (Ar)(X)] complexes arguably presents some disadvantages. In the course of our studies devoted to the investigation of the behavior of highly efficient palladium polyphosphane catalytic systems for cross-coupling reactions, 9] we anticipated the usefulness of electrosynthesis to provide a convenient access to important intermediates in organometallic catalysis. Based on reported mechanistic and kinetic studies on oxidative addition of iodobenzene to Pd polyphosphane complexes, the present report answers several important questions concerning the nature of oxidative addition products and the course of the reaction. It describes also a powerful and general electrosynthetic method for the straightforward isolation of oxidative addition intermediates. As a proof of concept, the characterization through X-ray solidstate structure and solution NMR of the iodophenyl intermediate [L1Pd ACHTUNGTRENNUNG(phenyl)(I)] (see complex 2 in Scheme 2), never isolated by standard chemical methods, is provided. The clean electrochemically driven oxidative addition of Ph I allowed us to recognize the perfect regioselectivity of the reaction. This selectivity was evidenced consistently by solution NMR and from a solid-state structure. The origin of this unexpected selectivity is discussed herein in the light of the specific conformation of the phosphorus donor atoms, and especially the hindrance of their phenyl substituents. As a first contribution to this field, we examined the initial step of general catalytic cycles in palladium-catalyzed cross-coupling reactions, that is, the oxidative addition of a formally electrophilic partner in the presence of tetraphosphane ligand L1 (see Scheme 2). In these studies, the reaction was initiated by the electrochemical reduction of stable palladium(II) dihalogenides, thus delivering the reactive palladium(0) species, which next readily activates a halogenated substrate, typically iodobenzene (Scheme 2). Some important information on the reaction mechanism was [a] Dr. V. A. Zinovyeva, C. Luo, S. Fournier, Dr. C. H. Devillers, Dr. H. Cattey, Prof. Dr. J.-C. Hierso, Prof. Dr. D. Lucas Universit de Bourgogne Institut de Chimie Mol culaire de l’Universit de Bourgogne (ICMUB) UMR-CNRS 5260, 9, avenue Alain Savary 21078 Dijon (France) Fax: (+33) 3-8039-3682 Fax: (+33) 3-8039-6025 E-mail : jean-cyrille.hierso@u-bourgogne.fr dominique.lucas@u-bourgogne.fr [b] Dr. H. Doucet Institut Sciences Chimiques de Rennes UMR-CNRS 6226, Campus de Beaulieu 35042 Rennes (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100629. Scheme 1. General synthetic routes to form Pd oxidative addition products of aryl halides stabilized by chelating diphosphanes.

Towards sustainable synthesis of pyren-1-yl azoliums via electrochemical oxidative C–N coupling

Electrosynthesis of 1-methyl-3-(pyren-1-yl)-1H-imidazol-3-ium tetrafluoroborate via oxidative C–N coupling of pyrene with methylimidazole is optimized with the aim to reduce waste and simplify the experimental setup. Several parameters are tested such as cell configuration (number of compartments), pyrene concentration, amount of nucleophile, electrosynthetic method (potentiostatic/galvanostatic), amount of electrons, atmosphere (Ar/air), solvent quality and presence/absence of a supporting electrolyte. The optimized conditions are successfully applied to the synthesis of 1-methyl-3-(pyren-1-yl)-1H-benzimidazol-3-ium tetrafluoroborate, 1-methyl-4-(pyren-1-yl)-1H-1,2,4-triazol-4-ium tetrafluoroborate and 3-(pyren-1-yl)-benzothiazol-3-ium tetrafluoroborate. These four pyren-1yl-azolium salts are characterized by NMR, MS, elemental analysis, UV-Vis absorption and emission spectroscopy. The X-ray crystallographic structures of 1-methyl-3-(pyren-1-yl)-1H-imidazol-3-ium tetrafluoroborate and 1-methyl-3-(pyren-1-yl)-1H-benzimidazol-3-ium tetrafluoroborate are presented.

Electrochemistry as an Attractive and Effective Tool for the Synthesis and Immobilization of Porphyrins on an Electrode Surface

Magnesium(II) 10-phenyl-5,15-p-ditolylporphyrin is easily and cleanly transformed by electrolysis. A nitro group is first introduced at the free meso position by anodic substitution. Hydrogenation into the amine is then carried out electrocatalytically under ambient conditions with water as a hydrogen supplier. The synthesized porphyrin under the nickel(II) form can be covalently grafted onto a platinum electrode by electrochemical reduction of the diazonium cation, generated in situ by a reaction of the nickel(II) aminoporphyrin with sodium nitrite and trifluoroacetic acid. The electrosynthesized thin film gives an electrochemical response typical of a porphyrin material. Films grown under our conditions have a maximum surface coverage of approximately 5×10(-10)  mol cm(-2). The modified electrode exhibits a reproducible electrochemical behavior and a good level of stability over potential cycling and exposition to air.

BODIPY–diketopyrrolopyrrole–porphyrin conjugate small molecules for use in bulk heterojunction solar cells

Two small molecules denoted as BD-pPor and BD-tPor composed of a central BODIPY core surrounded with two DPP and two porphyrin units have been designed and synthesized. In BD-pPor and BD-tPor, porphyrins are linked to the central BODIPY by phenyl and thiophene bridges, respectively. The optical and electrochemical properties were systematically investigated in order to employ them as donors along with PC71BM as an acceptor for solution processed bulk heterojunction organic solar cells. After the optimization of the active layer, the organic solar cells based on BD-pPor and BD-tPor exhibit overall power conversion efficiencies of 6.67% and 8.98% with an energy loss of 0.63 eV and 0.50 eV. The low value of energy loss for BD-tPor may be related to the low LUMO offset between the BD-tPor and PC71BM (0.31 eV) as compared to that between BD-pPor and PC71BM (0.36 eV). The low energy loss also leads to a higher value of open-circuit voltage for the BD-tPor based OSC than its BD-pPor counterpart, despite the slightly deeper HOMO energy level of BD-pPor. The enhanced values of Jsc and FF of the BD-tPor based OSCs may be related to the better exciton dissociation and charge transport, as confirmed from the PL spectra and charge carrier mobility. These results indicate that the combination of BODIPY, DPP and porphyrin in the same conjugate is very promising for small molecule organic solar cells.

Preparation of cobalt polyporphine and its catalytic properties in oxygen electroreduction

A new member of the polyporphine series—cobalt polyporphine of type I (pCoP-I)—was prepared from the starting magnesium polyporphine of type I (pMgP-I) by ion exchange, i.e. by sequential processing of the pMgP-I polymer film on the electrode surface with solutions of trifluoroacetic acid (forming metalfree polyporphine of type I, pH2P-I) and cobalt(II) acetate in organic solvents. The completeness of each stage of ion exchange can be judged from the change in the electrochemical and spectral characteristics of the obtained polymer films of unsubstituted porphine (?H2P-I) and cobalt porphine (pCoP-I) of type I. Oxidative transformation of this polyporphine pCoP-I was performed, which led to the formation of additional bonds between the neighboring porphine units in the polymer film (transition of polymer of type I into polymer of type II, pCoP-II). The behavior of the polymer films of cobalt polyporphine of types I and II in oxygen electroreduction was studied. The films showed catalytic activity in this process.

Synthesis and characterization of zinc carboxy–porphyrin complexes for dye sensitized solar cells

Two zinc porphyrins, 2 and 8, have been synthesized. Porphyrin 8 displays better electronic communication between the dye and the TiO2 electrode. Photophysical measurements and electrochemistry experiments suggest that both porphyrins are very promising sensitizers for dye-sensitized solar cells (DSSCs). It was found that their molecular orbital energy levels favor electron injection and dye regeneration in DSSCs. Solar cells sensitized by 2 and 8 were fabricated, and it was found that they show power conversion efficiencies (PCEs) of 5.27% and 7.13%, respectively. Photovoltaic measurements (J–V curves) together with the incident photon-to-electron conversion efficiency spectra of the two cells reveal that the higher PCE value of the DSSC based on 8 is ascribed to the higher short-circuit current (Jsc), open-circuit voltage (Voc), and dye loading values. Moreover, the larger charge recombination resistance, longer electron lifetime and shorter electron transport time for 8 also confirm the higher value of the Voc and the Jsc and the FF for the DSSC based on 8.