Rate and Mechanism of the Oxidative Addition of Benzoic Anhydride to Palladium(0) Complexes in DMF

The rate constant of the oxidative addition of the benzoic anhydride (PhCO)2O to [Pd0(PPh3)4] has been determined in DMF and compared to that of phenyl halides and phenyl triflate. The following reactivity order has been established: PhI >> (PhCO)2O > PhOTf > PhBr. The oxidative addition of (PhCO)2O proceeds by activation of one C−O bond. Two acyl-PdII complexes are formed: a neutral complex trans-[(PhCO)Pd(OCOPh)(PPh3)2] and a cationic complex trans-[(PhCO)PdS(PPh3)2]+ (S = DMF) showing that the decarbonylation process is highly endergonic. The exchange of PPh3 by the bidentate ligand dppp does not favor the decarbonylation process.

Synthesis of Unsymmetrical Heterobiaryls Using palladium-catalyzed cross-coupling reactions of lithium organozincates

International audienceSeveral unsymmetrical heterobiaryls have been synthesized through palladium-catalyzed cross-coupling reactions of lithium triorganozincates. The latter have been prepared by deprotonative lithiation followed by transmetalation using non hygroscopic ZnCl2*TMEDA (1/3 equiv)

A Convenient Approach to Luminescent Cyclometalated Platinum(II) Complexes with Organometallic π-Bonded Benzenedithiolate

International audienceA family of neutral cyclometalated platinum(II) complexes [(C^N)Pt(η-S^S)] with π-bonded benzenedithiolate {(η-S^S) = Cp*Ru(C6H4S2)} and various cyclometalated ligands, {(C^N) = 2-phenylpyridine (ppy), (2); 2,4-difluorophenylpyridine (F2ppy) (3), benzo[h]quinoline (bzq) (4); dibenzo[f,h]quinoline (dbzq) (5) } were prepared and fully characterized. For comparison purposes the related bipyridine platinum (II) complex [(bpy)Pt(η-S^S)][OTf] (6) was also prepared. The electrochemistry behavior of these complexes was investigated and shows the enhanced stability of these compounds toward oxidation due to the presence of Cp*Ru moiety which is now π-bonded to the benzenedithiolato group. Moreover several complexes were identified by single crystal X-ray molecular structures. To the best of our knowledge these are the first structures to be reported for cyclometalated platinum complexes with a π-bonded benzenedithiolate (bdt) ligand. All of the complexes are luminescent in fluid solution at room temperature and in glassy solution at 77 K; their emission properties can be tuned through ligand variation

Iron(II) catalyzed reductive radical cyclization reactions of bromoacetals in the presence of NaBH4: optimization studies and mechanistic insights

Abstract 5-Exo-trig radical reductive cyclization reactions of bromoacetals are catalyzed by iron in the presence of the reducing agent NaBH4. Both iron(II) and iron(III) were found to effectively mediate these reactions. As shown by cyclic voltammetry, iron(III) can be reduced to an iron(II) precatalyst before passing through an identical reaction mechanism in which monoelectronic activation of the substrate would occur by an anionic hydridoiron(I) complex. Further studies have established that both the substrate (iodo- vs bromo-derivative) and the precatalytic mixture are decisive in determining the reaction outcome

Elucidating dramatic ligand effects on SET processes: iron hydride versus Iron borohydride catalyzed reductive radical cyclization of unsaturated organic halides

An iron(II) borohydride complex ([(η1-H3BH)FeCl(NCCH3)4]) is employed as the precatalyst in iron-catalyzed radical cyclizations of unsaturated organic halides in the presence of NaBH4. Mechanistic investigations have established that the ligand bound to the metal center (acetonitrile versus ethylenebis(diphenylphosphine) (dppe)) plays a crucial role in the structure and reactivity of the active anionic iron(I) hydride ([HFeCl(dppe)2]−) and borohydride ([(η1-H3BH)FeCl(NCCH3)4]−) with unsaturated haloacetals. This work provides new insights into iron(I) hydride and borohydride species and their potential implication in single-electron processes

Etude mécanistique de réactions de couplage catalysées par des complexes du cuivre et du fer

L'utilisation de complexes du cuivre et du fer comme catalyseurs de réactions de couplage est d'un grand intérêrt en synth se organique du fait de leur faible coût et de leur basse toxicité. Dans cette th se sont étudiés dans un premier temps les mécanismes de formations de liaisons C-N et C-O catalysés par des complexes du cuivre. Ensuite, le rôle réel du fer dans la catalyse de la formation de liaisons C-N est étudié. Deux exemples de formation de liaisons C-C ferrocatalysées sont enfin étudiés: un couplage de Kochi entre un halogénure aromatique et un réactif de Grignard, ainsi qu'une réaction de cyclisation radicalaire. La voltammétrie cyclique, les modélisations théoriques par calculs DFT ainsi que les spectroscopies de RMN et de RPE ont été utilisés comme outils d'investigation.The use of copper and iron complexes as cross-coupling catalysts is now a challenge in today organic synthesis, due to their low cost and low toxicity. This work, in a first part, deals with mechanistic insights into C-N and C-O cross-couplings catalyzed by copper complexes. In a second part, the true role of iron in C-N cross-couplings processes is investigated. In a third part, two examples of iron-catalyzed C-C bond formations are investigated: a Kochi-type coupling between an aryl halide and a Grignard reagent, and a radical carbocyclization. Cyclic voltammetry, theoretical DFT calculations, NMR and EPR spectroscopies have been used as investigation tools.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Transition Metal‐Catalyzed Carbon–Carbon Cross‐Coupling

International audienc

Réactions catalysées par Pd(oAc)2/benzoquinone (un procédé général pour l'activation de liaisons Ar-H, Ar-B et C-H, via une oxydation électrochimique)

Le principal problème lié aux réactions catalysées par le palladium (II) est qu au cours du cycle catalytique, du palladium (0) est libéré, ce qui impose la présence d un oxydant permettant la régénération du Pd(II). Des méthodes de recyclage existantes impliquent généralement l utilisation d oxydants chimiques en quantité stœchiométrique. La formation de produits secondaires, et le caractère souvent toxique de ces composés nous ont poussés à trouver une alternative plus douce, plus économique en atomes et généralisable à diverses réactions. Nous proposons ici une voie électrochimique de recyclage du catalyseur, via l utilisation d une quantité catalytique de p benzoquinone. Cette méthode permet d éviter la présence d oxydants chimiques pouvant être nuisibles à la réaction. Ce procédé a été mis au point pour trois réactions différentes de synthèse organique, qui sont : les réactions de type Heck à partir d arènes, la synthèse de biaryles par homocouplage de dérivés organoborés et enfin, l oxydation d alcools en aldéhydes et cétones.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF