Search results for "PALLADIUM"
showing 10 items of 956 documents
Generation, Characterization, and Electrochemical Behavior of the Palladium-Hydride Cluster [Pd3(dppm)3(3-CO)(3-H)]+ (dppm=Bis(diphenylphosphinometha…
2007
Addition of formate on the dicationic cluster [Pd(3)(dppm)(3)(mu(3)-CO)](2+) (dppm=bis(diphenylphosphinomethane) affords quantitatively the hydride cluster [Pd(3)(dppm)(3)(mu(3)-CO)(mu(3)-H)](+). This new palladium-hydride cluster has been characterised by (1)H NMR, (31)P NMR and UV/Vis spectroscopy and MALDI-TOF mass spectrometry. The unambiguous identification of the capping hydride was made from (2)H NMR spectroscopy by using DCO(2) (-) as starting material. The mechanism of the hydride complex formation was investigated by UV/Vis stopped-flow methods. The kinetic data are consistent with a two-step process involving: 1) host-guest interactions between HCO(2) (-) and [Pd(3)(dppm)(3)(mu(3…
Synthesis and crystal structures of palladium(II) complexes of 1,11-bis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane-5,7-dione
2001
The two palladium(II) complexes, [PdL22222][ClO4]2·H2O 1 and [Pd(H−2L22222)]·H2O 2 with 1,11-bis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane-5,7-dione, L22222, were prepared and characterized by X-ray crystallography and UV-visible spectroscopy. In 1 the palladium centre is co-ordinated by the tertiary amines of the macrocycle and the two pyridylmethyl nitrogens, forming a square-planar geometry in which two amide nitrogen groups remain protonated and do not take part in co-ordination. Moreover, there is a weak interaction between palladium and H(–N(8)) [d(PdII ⋯ H) = 2.90 A]. In contrast, 2 isolated under basic conditions has a square-planar geometry but the palladium ion is co-ordi…
(2,2‐Dibromovinyl)ferrocene as a Building Block for the Assembly of Heterodinuclear Complexes – Preparation of an σ‐Alkenylpalladium Complex and Dime…
2007
The oxidative addition of (2,2-dibromovinyl)ferrocene [Br2C=C(H)–Fc] (1) to [Pd(PPh3)4] yields the heterodinuclear σ-alkenyl complex trans-[{Pd(Br)(PPh3)2}–C(Br)=C(H)–Fc] (2). Nucleophilic attack of sodium thiolates on 1 unexpectedly affords the vinyl thioether derivatives (Z)-[(RS)(H)C=C(H)–Fc] (4a: R = Ph; 4b: R = tBu; 4c: R = Et). Complexes 4a and 4c can also be prepared by addition of NaSR across the triple bond of Fc–C≡C–H (3). Addition of an excess of NaSR to 1 affords the dithioether derivatives (Z)-[(RS)(H)C=C(SR)–Fc] (5a: R = Ph; 5b: R = p-tolyl; 5c: R = Et). An addition/elimination sequence is suggested to account for this surprising result. The yield of 5c is very low due to a co…
Synthesis of the first imidazolyl-triphosphines containing a Triphos unit
2007
Abstract Since biphasic liquid–liquid continuous-flow catalytic processes often require the use of cationic phosphine ligands for the metal sequestration in the polar phase, we have prepared the first imidazolyl triphosphines, named Triphosim and Triphosmim. These ligands contain the Triphos unit [-P(CH2CH2PPh2)] which is linked to the imidazole fragment and have been obtained in three steps from imidazole (or 2-methylimidazole), diethylvinylphosphonate and diphenylvinylphosphine with global yields of 42–48%. The Triphosim ligand adopts a tridentate P-coordination mode in a palladium dichloride complex and the reaction of the dangling imidazole function with alkyl halides leads to a new kin…
Stability of Dinuclear Phosphane Palladium(III) Complexes: A DFT Approach
2018
Computational density functional theory studies have been carried out for the dinuclear ortho-metalated palladium(III) compounds [Pd2{μ-(C6H4)PPh2}2{μ-(X1-X2)}2Cl2]. These studies have shown that the electronic and steric properties of the auxiliary ligands (X1-X2 = bridging (carboxylato) or chelating (phenolato/acetylacetonato) O,O-donor ligands, bridging N,N-donor ligands (triazenido/formamidinato/pyrazolato), and bridging N,S-donor ligands) lead to systematic trends in their stability, highlighting that (a) the electronic nature of the donor atoms trans to the P has a clear trend, the replacement of hard donor atoms (O, N) by softer S donors generally reducing the stability of the compou…
Synthesis and application of new iminopyridine ligands in the enantioselective palladium-catalyzed allylic alkylation
2014
A variety of iminopyridines were obtained by condensation of chiral amines with pyridine-2-carboxaldehyde and quinoline-8-carbaldehyde, or of aminoalkylpyridine derivatives with chiral ketones. These ligands were assessed in the enantioselective palladium catalyzed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate affording the product dimethyl 1,3-diphenylprop-2-enylmalonate in good yields and moderate enantioselectivities (up to 62% ee). Catalytic activity and enantioselectivity were found to be highly dependent upon the steric properties of the ligands. The best enantioselectivity (62% ee) was obtained by an iminopyridine based on a camphane skeleton. © 2014 …
Self-Sorting Effects in the Self-Assembly of Metallosupramolecular Rhombi from Chiral BINOL-Derived Bis(pyridine) Ligands
2013
Four BINOL-based bis(4-pyridyl) ligands were synthesised in enantiopure and racemic form. These ligands form metallosupramolecular [(dppp)2M2L2] rhombi with cis-protected [(dppp)Pd]2+ and [(dppp)Pt]2+ ions. In principle, racemic ligands can self-assemble into three stereoisomeric rhombi. The degree of self-sorting in the self-assembly process crucially depends on the substitution pattern and the resulting bend angle of the V-shaped ligands as well as the degree of steric crowding within the assembly when racemic ligands are used. Thus, these processes either lead to homochiral assemblies in a narcissistic self-recognition manner, to heterochiral assemblies in a social self-discriminating ma…
The oligomerisation of 3-hydroxy-1-alkynes with palladium(II) diketonates and phosphorus ligands as the catalytic system
1993
Abstract 3-Methylhex-1-yne-3-ol has been oligomerised by use of Pd(II) acetylacetonate with 31 different phosphorus ligands as catalyst, yielding a dimer (2,4-disubstituted but-1-en-3-yne) and a linear trimer (1,4,6-trisubstituted hexa-1,3-dien-5-yne) as the two main products. By input-output relations a variation of the diketonate and the P ligand, as weil as an alteration of the phosphorus/palladium ratio, has been connected with product ratios as dependent variables. Phosphines produced three association steps up to a cone angle of 170°; the third step representing a stop complex. For the first association the activity of the catalytic system and the portion of the 2,4-dimer increased wi…
Unexpected self-assembly of a homochiral metallosupramolecular M4L4 catenane
2014
Two enantiomerically pure 9,9'-spirobifluorene-based bis(pyridine) ligands 1 and 2 were prepared to study their self-assembly behavior upon coordination to cis-protected palladium(II) ions. Whereas the sterically more demanding ligand, 2, gave rise to the expected dinuclear metallosupramolecular M2L2 rhombi, the sterically less demanding ligand, 1, acts as a template to give rise to a homochiral metallosupramolecular M4L4 catenane.
Ab initio study of structure and energetics of species involved in the 2,4-dinitro-toluene hydrogenation on Pd catalysts
2002
Abstract Quantum-mechanical calculations, at HF level, were performed to gain chemical–physical basis information on the 2,4-dinitro-toluene hydrogenation occurring over palladium catalysts. To investigate the surface characteristics of the species involved in the reaction system, simplified molecular models including small metal clusters were considered. Remarkable findings, useful to elucidate the reaction mechanism and important parameters, working in time dependent Monte-Carlo simulations of the title reaction, were obtained; inter alia: the molar standard free energies of the molecules involved in the reaction, the volume occupied by the species in solution phase and the qualitative or…