1,720,994 research outputs found
Complessi di Pd(0) contenenti leganti imino-fosfinici come catalizzatori per la reazione di Stille
No full textComplessi di Pd(0) contenenti leganti imino-fosfinici come catalizzatori per la alcossicarbonilazione di alchini terminali
No full textIminophosphine-palladium systems for the cross-coupling of vinyl stannanes with aryl halides
No full textReazioni di 'cross coupling' di alchinilstannani con alogenuri arilici catalizzate da complessi imminofosfinici di palladio(0)
No full text[PdCl2{8-(di-tert-butylphosphinooxy)quinoline)}]: a highly efficient catalyst for Suzuki–Miyaura reaction
No full textThe complex [PdCl2(P–N)] containing the basic and sterically demanding 8-(di-tert-butylphosphinooxy)-quinoline ligand (P–N) is a highly efficient catalyst for the coupling of phenylboronic acid with arylbromides or aryl chlorides. The influence of solvent and base has been investigated, the highest rates being observed at 110 C in toluene with K2CO3 as the base. With aryl bromides the reaction rates are almost independent on the electronic properties of the para aryl substituents, on the contrary, reduced reaction rates are observed when bulky substituents are present on the substrate. Nevertheless the
coupling of 2-bromo-1,3,5-trimethylbenzene with phenylboronic acid can be carried out to completion in 2 h using a catalyst loading of 0.02 mol %. Under optimized reaction conditions, turnover frequencies as high as 1900 h1 can be obtained in the coupling of 4-chloroacetophenone with phenylboronic acid;
lower reaction rates are obtained with substrates bearing EDG substituents on the aryl group
Iminophosphine-palladium(0) Complexes as Catalysts for the Stille Reaction
No full textThe cross-coupling of iodobenzene with tributylphenylethynylstannane or tributylvinylstannane is efficiently catalysed by
iminophosphine–palladium(0)–olefin complexes of the type [Pd(h2-dmf)(P-N)] (dmf, dimethylfumarate; P-N, 1-(PPh2)-C6H4-2-CvNR
(R1⁄4alkyl, aryl)). The catalytic activity depends on the R substituent of the imino group: the highest reaction rates are obtained using arylsubstituted
iminophosphines. Equivalent catalytic systems can be obtained using a palladium source such as Pd(OAc)2 or Pd(dba)2
(dibenzylideneacetone, dba) in combination with the iminophosphine ligands. In the coupling of iodobenzene with tributylphenylethynylstannane,
the highest reaction rates are obtained using an iminophosphine/palladium molar ratio of 2:1, while in the vinylstannane–
iodobenzene coupling the best P-N/Pd ratio is 1:1. q 2002 Elsevier Science Ltd. All rights reserved
Structural studies on iminophosphine ligands and their palladium complexes
No full textThe crystal and molecular structures of the iminophosphine o-(Ph2P)C6H4CH=NC6H4OMe-4 (1) and its palladium complexes [Pd(3-C3H5){o-(Ph2P)C6H4CH=NC6H4OMe-p}]BF4 (2) and [Pd(2-fn){o-(Ph2P)C6H4CH=NC6H4OMe-4}] [fn=fumaronitrile, (3)] have been determined by X-ray analysis. In the free ligand (1), the planar imino group of E configuration is oriented, relative to the PPh2 unit, so that the CH=N hydrogen atom points towards phosphorus, with the nitrogen atom on the opposite side. In (2) and (3) the iminophosphine behaves as a P,N-chelate ligand, this coordination mode being achieved by the imino group rotation of 169.3° and 145.3°, respectively, around its bond with the ortho disubstituted phenyl ring. Complex (2) shows a structural disorder with two different orientations of the allyl ligand. The trigonal planar coordination around the central metal in complex (3) involves the P- and N-donor atoms of (1) and the 2-bound olefin, with a marked lengthening of the olefinic carbon-carbon bond. In both the complexes, the chelate six-membered ring of the iminophosphine with palladium is not coplanar with the N-Pd-P coordination plane, the imino carbon atom and the ortho disubstituted phenyl group lying on the same side out of the N-Pd-P plane, whereas the N-substituent and one of the PPh2 groups are on the opposite side. The 1H-n.m.r. spectra at low temperatures of (2) and (3), and of [Pd(2-tmetc){o-(Ph2P)C6H4CH=NCMe3}] [tmetc=tetramethyl ethylenetetracarboxylate, (4)] are interpreted on the basis of a non-rigid conformation of the chelate iminophosphine, which undergoes a fast dynamic process whereby the N- and P-substituents move above and below the coordination plane
Polynuclear complexes of palladium(II) with halogen and sulfur bridges
No full textThe reaction of Na2[PdCl4] with Ph2S2 in MeOH yields a polymeric compd. of formula [Pd(SPh)Cl]n (I) contg. alternating
halogen and S bridges. This compd. is also formed by refluxing [Pd(Ph2S2)-Cl2]2 in MeOH. The characterization of I was based on its ir spectra and on its bridge-splitting reactions. In the reaction of I with a neutral ligand L (L = pyridine, Ph3P, Ph3As) S-bridged complexes of the type [Pd(SPh)LCl]2 are formed. The reaction with ethylenediamine yields the cationic S-bridged complex [Pd(SPh)(en)]2Cl2, whereas with [AsPh4]Cl the anionic complex [Pd(SPh)Cl2]2[AsPh4]2 is formed. The above reactions involve only splitting of the Cl-Pd bridges. When I reacts either with 1,2- bis(diphenylphosphino)ethane or with an excess of phosphine, both the halogen and S bridges are cleaved. The nature of the products in the bridge-splitting reactions has been detd. on the basis of elemental anal., ir spectra, cond., and mol.
wt. measurements, where possible
Five-coordinate complexes of palladium(II) and platinum(II) with alpha-diimine and 1,5-cyclooctadiene ligands
No full textThe five-coordinate complexes [PtMe(cod)(N-N')]BF4 [cod = eta(2), eta(2)-cyclooctadiene, N-N' = (6-R-2)C5H3N-2-CH=NR1 (R-1 = C6H4OMe-4, R-2 = H (1), Me (2); R-1 = CMe3, R-2 = H (3), Me (4); R-1 = (R)-bornyl, R-2 = Me (5))] are readily obtained from the reaction of [PtClMe(cod)] with N-N' in the presence of NaBF4. The preparation of [PtMe(cod)(6)]BF4 (6 = 4-MeOC6H4N=CHCHN=C6H4OMe-4), [PdMe(cod)(N-N')] BF4 and [PtCl(cod)(N-N')]BF4 (N-N' = 2, 4) requires chloride abstraction by AgBF4 from [PtClMe(cod)], [PdClMe(cod)] and [PtCl2(cod)], respectively, followed by coordination of N-N'. The NMR spectral data suggest a trigonal-bipyramidal structure with chelating cod and N-N' ligands, where the alpha-diimine and one C=C bond are on the equatorial plane and the second C=C bond in an axial position. The complexes [PtMe(cod)(1)]BF4 and [PtCl(cod)(2)]BF4 undergo dynamic processes in solution which bring about N-N' ligand site exchange for the former, and exchange of all the olefinic protons for the latter. The X-ray diffraction analysis of [PtMe(cod)(2)]BF4 indicates that in the solid state, the complex assumes a distorted trigonal-bipyramidal geometry, similar to that proposed to exist in solution. For the two independent molecules in the asymmetric unit cell, the differences in the structural parameters between the equatorial Pt-(CH=CH) bond [Pt-C2.08(1), 2.09(2) Angstrom, C=C 1.43(2) Angstrom (molecule I); Pt-C 2.13( 2), 2.10(2) Angstrom, C=C 1.42(2) Angstrom (molecule II)] and the axial Pt-(CH=CH) bond [Pt-C 2.35(1), 2.34(1) Angstrom, C=C 1.39(2) Angstrom (molecule I); Pt-C 2.37(2), 2.34(1) Angstrom, C=C 1.38(2) Angstrom (molecule II)] are related to the high trans influence of the methyl ligand and to greater d-pi back-donation in the equatorial bond
- …
