PdI Complex Research Articles

Palladium‐Catalyzed Allylic Substitution: Reversible Formation of Allyl‐Bridged Dinuclear Palladium(I) Complexes

ESI-MS monitoring of the title reaction has led to the discovery that dinuclear allyl-bridged PdI complexes are formed reversibly in substantial amounts during catalysis (see scheme; Bz=benzoyl). The structure of one such complex was determined by X-ray analysis (see picture; P yellow, N blue, O red, Pd dark gray). Upon consumption of the starting materials a new dinuclear complex resulting from reductive C[BOND]Cl bond cleavage of CH2Cl2 was observed.

A Dinuclear Palladium(I) Ethynyl Complex: Synthesis, Structure, and Dynamics

The reaction of Pd(η3-C3H5)2 with PiPr3 at −30 °C affords yellow crystals of the PdII complex (iPr3P)Pd(η3-C3H5)(η1-C3H5) (1). At 20 °C 1 transforms into the dinuclear PdI complex {(iPr3P)Pd}2(μ-C3H5)2 (2) due to oxidative C−C coupling of two allyl groups with elimination of 1,5-hexadiene. Heating 1 or 2 in 1,6-heptadiene to 80 °C produces the Pd0 complex (iPr3P)Pd(η2,η2-C7H12) (3). {(η3-C3H5)PdCl}2 reacts with iPr3P to give (iPr3P)Pd(η3-C3H5)Cl (4b), from which further derivatives (iPr3P)Pd(η3-C3H5)X (X = OSO2CF3 (4a), C⋮CH (5a), CH3 (5b)) are obtained by replacement reactions. The mononuclear PdII-acetylide 5a and complex 3 combine to give the dinuclear PdI derivative {(iPr3P)Pd}2(μ-C3H5)(μ2-η2-C2H) (6). The Pd−Pd bond in 6 is unsymmetrically bridged by a π-allyl and a σ−π-ethynyl group, as determined by X-ray structure analysis. The structures of 1, 4a,b, and 6 are dynamic in solution, with 1 undergoing an exchange of the binding modes of the π- and σ-coordinated allyl groups and 4a,b displaying a π/σ-...

Identification of a novel saturable endoplasmic reticulum localization mechanism mediated by the C-terminus of a Dictyostelium protein disulfide isomerase.

Localization of soluble endoplasmic reticulum (ER) resident proteins is likely achieved by the complementary action of retrieval and retention mechanisms. Whereas the machinery involving the H/KDEL and related retrieval signals in targeting escapees back to the ER is well characterized, other mechanisms including retention are still poorly understood. We have identified a protein disulfide isomerase (Dd-PDI) lacking the HDEL retrieval signal normally found at the C terminus of ER residents in Dictyostelium discoideum. Here we demonstrate that its 57 residue C-terminal domain is necessary for intracellular retention of Dd-PDI and sufficient to localize a green fluorescent protein (GFP) chimera to the ER, especially to the nuclear envelope. Dd-PDI and GFP-PDI57 are recovered in similar cation-dependent complexes. The overexpression of GFP-PDI57 leads to disruption of endogenous PDI complexes and induces the secretion of PDI, whereas overexpression of a GFP-HDEL chimera induces the secretion of endogenous calreticulin, revealing the presence of two independent and saturable mechanisms. Finally, low-level expression of Dd-PDI but not of PDI truncated of its 57 C-terminal residues complements the otherwise lethal yeast TRG1/PDI1 null mutation, demonstrating functional disulfide isomerase activity and ER localization. Altogether, these results indicate that the PDI57 peptide contains ER localization determinants recognized by a conserved machinery present in D. discoideum and Saccharomyces cerevisiae.

Mechanisms of synthesis of maleic and succinic anhydrides by carbonylation of acetylene in solutions of palladium complexes

The mechanism of synthesis of maleic and succinic anhydrides from acetylene and CO in the PdBr2−LiBr-organic solvent catalytic system was studied using the procedure of advancement and discrimination of hypotheses. The hypotheses were obtained using the data bank on elementary steps and the Combl combinatorial program. The discrimination of the hypotheses was based on the data of NMR and IR spectroscopy, studies of isotope exchange, the role of potential organic intermediates, the kinetic isotope effect, and one-factor kinetic experiments. The most probable mechanism of synthesis of maleic anhydride includes insertion of acetylene and CO into the Pd−Pd bond of the PdI complex, which is formed from PdII at the initial step of the process. Succinic anhydride results from the intramolecular transformation of the hydride complex of palladium and maleic anhydride. The palladium hydride complexes detected in the contact solution apparently play the crucial role in the conjugation of oxidation, reduction, and addition type reactions.

Adsorbate interactions of paramagnetic palladium species in PdII-exchanged H-rho zeolite characterized by EPR and electron spin echo modulation spectroscopies

Interactions of paramagnetic palladium ions in H-rho zeolite with oxygen, water, methanol, ethanol, propanol, ammonia, carbon monoxide, hydrogen, ethene, benzene and pyridine have been studied by EPR and electron spin echo modulation (ESEM) spectroscopies. PdII was reduced to paramagnetic PdI by a thermal activation process. The EPR spectrum of an activated sample shows the formation of one PdI species, which is suggested to be located in octagonal prism sites of the rho zeolite framework. PdI interacts with water vapour or molecular oxygen, to form PdII–O2–, indicating the decomposition of water. Equilibration with methanol, ethanol or propanol results in a broad isotropic EPR signal which is attributed to the formation of small palladium clusters. ESEM shows that the Pd clusters coordinate to one molecule of methanol or ethanol. Interestingly, an activated sample with adsorbed ethanol produces an additional anisotropic signal, besides the broad isotropic signal, which is also coordinated to one molecule of ethanol. Propanol requires relatively much longer times for cluster formation, compared with methanol and ethanol. Adsorption of ammonia produces a PdI complex containing four molecules of ammonia, based upon resolved nitrogen superhyperfine coupling. Adsorption of carbon monoxide results in a PdI complex containing two molecules of carbon monoxide, based upon resolved 13C superhyperfine coupling. Upon adsorption of hydrogen, a new PdI species occurs, which disappears upon exposure to oxygen. EPR and ESEM results indicate that exposure to ethene leads to two new PdI species, each of which coordinates to one molecule of ethene.

PdIlocation and adsorbate interactions in PdH-SAPO-34 studied by EPR and electron spin–echo modulation spectroscopies

EPR and electron spin–echo modulation (ESEM) spectroscopies have been used to monitor the location of PdI and its interaction with water, methanol, ethanol, ethene, benzene, carbon monoxide and ammonia in sili-coaluminophosphate type 34 (SAPO-34) molecular sieve containing PdII by ion exchange. After activation at 600 °C, three different PdI species are observed: A1(g⊥= 2.177), A2(g⊥= 2.070) with a common g‖= 2.92. These correspond to three different site locations in the framework. A1 is assigned to the least accessible site III in the centre of a hexagonal prism, A3 to site I displaced from a six-ring into the ellipsodial cage and A2 to the most accessible site IV near an eight-ring window based on adsorption of oxygen and hydrogen and 31P modulations from the SAPO framework observed by ESEM. Oxygen and water oxidize PdI ions in an activated sample to PdII ions complexed to O2–, indicating water decomposition. Adsorption of methanol and ethanol causes a change in the EPR spectrum which indicates some relocation of PdI to allow better coordination with one molecule of the alcohol. Exposure to ethene also changes the EPR spectrum, indicating interaction of PdI with it. ESEM shows that the PdI species coordinates to one ethene molecule. The adsorption of carbon monoxide results in a PdI complex with three molecules of carbon monoxide based on resolved 13C superhyperfine splittings. Upon adsorption of ammonia, one molecule of ammonia coordinates to PdI based on resolved nitrogen hyperfine coupling.

Alkoxycarbonyl, acyl, and alkyl complexes of nickel(II) and palladium(II)

Oxidative addition of haloformates and acyl halides to Pd (CNBut)2, Pd (PPh3)4, Ni (CNBut)4, and Ni (PPh3)4 gave ROCO-, RCO-, and R-PdII or NiII complexes and some PdI and NiI complexes.