Synthesis and characterization of palladacyclopentadiene complexes with N-heterocyclic carbene ligands

New palladacyclopentadiene compounds containing different chelate NHC-thioether and NHC-pyridine ligands have been prepared by transfer of the functionalized carbenes from the respective silver complexes to the polymeric precursors [PdC-COOR)4]n (R = Me, t-Bu). Their dynamic behaviour in solution was discussed and the solid-structure of 2c was determined by X-ray crystallography. The treatment of [Pd(C-COOCH3)4]n with two equivalents of the carbene silver complexes led to the (NHC)2Pd(C4-COOCH3)4 derivatives (3cei), a new class of compounds with only PdeC bonds. A serious limitation to this synthetic procedure is an excessive steric crowding around the metal centre. The complexes 3 are present in solution as a mixture of two atropoisomers, due to restricted rotation around the CarbeneePd bond. The kinetics of equilibration between the two configurational isomers was studied for complex 3c, which was also structurally defined by X-ray crystallography (anti isomer). Finally a synthetic protocol was set up for the synthesis of mixed NHC-Phosphine and NHC-Isocyanide palladacyclopentadiene complexes. In this procedure the order of addition of the reactants is of great importanc

Computational investigations on the unexpected extrusion of molecular iodine in Pd(II) σ-butadienyl complexes

4reservedmixedSCATTOLIN, THOMAS; VISENTIN, Fabiano; CANOVESE, Luciano; SANTO, ClaudioScattolin, Thomas; Visentin, Fabiano; Canovese, Luciano; Santo, Claudi

Reactions of palladium(0) olefin complexes stabilized by some different hetero- and homo-ditopic spectator ligands with propargyl halides

Several new allenyl and propargyl complexes have been obtained by oxidative addition with propargyl chlorides of palladium (0) olefin complexes stabilized by N−N, P−P, N−P, N−S. and N−C homo− and hetero−ditopic spectator ligands. The oxidative addition of some of the isolated palladium(0) olefin derivatives with 3−chloro−1−propyne and 3−chloro−1− phenyl−propyne has been investigated and the ensuing tautomeric mixtures bearing propargyl and allenyl fragmenst η1− coordinated isolated. As a consequence of a detailed kinetic study, we have analyzed the influence of the electronic and steric parameters of the involved reactants and hypothesized the mechanism of reaction. The tautomeric rearrangement of one allenyl isomer into its propargyl counterpart was also investigated and in this case the complete determination of all the rate constants involved has been obtained. Beside these studies, two very rare η3−propargyl palladium derivatives have been isolated and characterized

Halogen metathesis in Pd(II) σ-butadienyl complexes

4reservedmixedSCATTOLIN, THOMAS; VISENTIN, Fabiano; CANOVESE, Luciano; SANTO, ClaudioScattolin, Thomas; Visentin, Fabiano; Canovese, Luciano; Santo, Claudi

Reactivity of N-heterocyclic carbene-pyridine palladacyclopentadiene complexes toward halogen addition. the unpredictable course of the reaction

As an extension of a previously published work we have reacted some palladacyclopentadiene complexes stabilized by bidentate N-heterocyclic carbene-pyridine or monodentate N-heterocyclic carbene-pyridine and isocyanide ligands with the halogens I2 and Br2. All the bidentate and monodentate complexes react with halogens to give at first the expected Ï\u83-coordinated butadienyl fragment. However, two of the less hindered NHC carbene-pyridine bidentate butadienyl iodo derivatives undergo a further rearrangement and novel Pd(ii) complexes characterized by a ten term coordinative ring were isolated and characterized. In the most favorable case we were able to carry out the kinetics of rearrangement and measure its reaction rate. Moreover, we have surmised a plausible mechanism on the basis of a dedicated computational approach and in one case the surprising structure characterized by the ten term coordinative ring was resolved by X-ray diffraction

Synthesis, Stability Constant Determination, and Structural Study of Some Complexes of a Zinc Triad Containing Pyridyl-amine-quinoline and Pyridyl-thio-quinoline

The potentially fluorescent and terdentate ligands containing nitrogen or sulfur as coordinating atom were synthesized and used in the formation of perchlorate or chloride complexes of the metals of the Zn triad. The reaction of the ligands with metal perchlorate salts yields the corresponding bis-chelate derivatives, whereas the same ligands react with metal chloride salts to give monochelate complexes. All of these complexes undergo NMR-scale fast fluxional rearrangement in solution. Some structural X-ray diffractometric studies were also performed and the ensuing data confirm the surmised structures and the solution rearrangement in the case of monochelate substrates and of one Hg derivative, respectively. The equilibrium constants of formation in the case of monochelate derivatives were also determined in water by means of spectrophotometric titration of the studied ligand with the metal ions. The values of the equilibrium constants were confirmed by supplementary determination taking into account the exchange between two different metals and/or dissociation equilibria. The fluorescence activity of ligands and complexes was eventually studied and notably one fluorescent silent ligand gives rise to fluorescent zinc derivatives