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Corresponding Complexes (corresponding + complex)
Selected AbstractsAn Atropo-Stereogenic Diphosphane Ligand with a Proximal Cationic Charge: Specific Catalytic Properties of a Palladium Complex ThereofEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2008Nathalie Debono Abstract A class of cationic diphosphane ligands combining phosphane and amidiniophosphane moieties is illustrated on the N -methyl,N -naphthylbenzimidazolium framework. The palladium(II) complex thereof is described and compared to the corresponding complex of the analogous neutral diphosphane. Contrary to first-level expectations, the N2C,P and N2CP,Pd bonds in the cationic diphosphane complex are not longer than those occurring in its neutral counterpart. In the cationic ligand, the proximal positive charge is indeed conjugated to one phosphanyl group, and the coordination scheme is tentatively interpreted by resonance of the phosphane,metal dative bond (+N2C,P:,[Pd]) with a carbene,phosphenium dative bond (N2C:,[+P:,Pd]). Despite this peculiar structural feature, the electronic , donation (vs. , acceptation) towards the palladium centre remains lowered in the cationic ligand. This specific property can be a priori valuable in a catalytic process where oxidative addition is not the limiting step. It is indeed shown that although the neutral complex is more active in Suzuki coupling reactions, the cationic complex is more active in Sonogashira-type coupling reactions involving predissociated halide substrates, namely an acyl chloride. These likely atropo-chiral ligands deserve to be resolved for application in asymmetric catalysis.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Computing a partial generalized real Schur form using the Jacobi,Davidson methodNUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 3 2007Tycho van Noorden Abstract In this paper, a new variant of the Jacobi,Davidson (JD) method is presented that is specifically designed for real unsymmetric matrix pencils. Whenever a pencil has a complex conjugate pair of eigenvalues, the method computes the two-dimensional real invariant subspace spanned by the two corresponding complex conjugated eigenvectors. This is beneficial for memory costs and in many cases it also accelerates the convergence of the JD method. Both real and complex formulations of the correction equation are considered. In numerical experiments, the RJDQZ variant is compared with the original JDQZ method. Copyright © 2007 John Wiley & Sons, Ltd. [source] Design your own elastomeric or stereoregular polymer,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10-12 2002Michal Shmulinson Abstract This study reports the synthesis and activity as precatalysts for the polymerization of propylene of five racemic group 4 complexes, cis-[p-R,C6H4C(NR)2]2MX2 (R,,=,CH3, R,=,SiMe3, M,=,Ti, X,=,Cl (1); R,,=,CH3, R,=,SiMe3, M,=,Zr, X,=,Cl (2); R,,=,H, R,=,i-pr, M,=,Zr, X,=,Cl (3); R,,=,CH3, R,=,SiMe3, M,=,Zr, X,=,CH3 (4)) and (acac)2MCl2 (M,=,Ti (5), M,=,Zr (6)) (acac,=,acetylacetone). The hydrocarbyl complex 4 was prepared by the alkylation of the corresponding complex 2 with MeLi·LiBr. Reaction of complex 4 with B(C6F5)3 or all complexes with MAO (MAO,=,methylalumoxane) results in the formation of a "cationic" intermediate complex which rapidly reacts with the incoming monomer. Some of the complexes catalyze the stereoregular polymerization of propylene only under pressure in either toluene or CH2Cl2, producing polypropylene with very large isotacticities (mmmm %,=,,95,98), high melting points (140,154,°C) and similar molecular weights as compared with cyclopentadienyl complexes, whereas complex 5 is active for the polymerization of elastomeric polypropylene. Copyright © 2003 John Wiley & Sons, Ltd. [source] Design of Neutral Metallomesogens from 5,5-Dimethyldipyrromethane: Metal Ion Mediated Control of Folding and Hairpin StructuresEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 32 2008Kelly A. Ames Abstract New ligands derived from 5,5-dimethyldipyrromethane and their corresponding neutral complexes with ZnII and PdII are described. The ligands incorporate either a hexacatenar [H2(1n), n = 1, 10, 12, 14 and 16], tetracatenar [H2(2n), n = 1 and 16] or an extended dicatenar structure [H2(3n), n = 1and 16]. Single-crystal X-ray structure determinations of [Zn2(11)2] and [Zn2(31)2] confirm a distorted tetrahedral geometry at ZnII to afford double-stranded helical structures, while the PdII species [Pd(31)] shows a distorted square-planar geometry with the ligand adopting an alternative hairpin conformation. The metal-free hexacatenar ligands H2(1n) (n = 10, 12, 14, 16) and the corresponding complexes [Zn2(116)2] and [Pd(1n)] (n = 12, 14, 16) are not mesomorphic. However, the tetracatenar complex [Zn2(216)2] generates a smectic mesophase, as confirmed by X-ray diffraction, while [Pd(216)] and the metal-free ligand H2(216) show no mesomorphic behaviour. Two of the extended dicatenar compounds, H2(316) and [Zn2(316)2] are non-mesomorphic, while [Pd(316)] displays a smectic A phase.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Tuning of Copper(I),Dioxygen Reactivity by Bis(guanidine) Ligands,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2005Sonja Herres-Pawlis Abstract A series of bis(guanidine) ligands designed for use in biomimetic coordination chemistry, namely bis(tetramethylguanidino)-, bis(dipiperidinoguanidino)-, and bis(dimethylpropyleno)propane (btmgp, DPipG2p and DMPG2p, respectively), has been extended to include bis(dimethylethyleneguanidino)propane (DMEG2p), which has both Namine atoms of each guanidine functionality connected by a short ethylene bridge, as a member. From this series, a family of novel bis(guanidine)copper(I) compounds , [Cu2(btmgp)2][PF6]2 (1), [Cu2(DPipG2p)2][PF6]2 (2), [Cu2(DMPG2p)2][PF6]2 (3), and [Cu2(DMEG2p)2][PF6]2·2MeCN (4) , has been synthesised. Single-crystal X-ray analysis of 1,4 demonstrated that these compounds contain dinuclear complex cations that contain twelve-membered heterocyclic Cu2N4C6 rings with the Cu atoms being more than 4 Å apart. Each copper atom is surrounded by a set of two N-donor functions from different ligands, resulting in linear N,Cu,N coordination sites. Depending on their individual substitution patterns, the guanidine moieties deviate from planarity by characteristic propeller-like twists of the amino groups around their N,Cimine bonds. The influence of these groups on the reactivity of the corresponding complexes 1,4 with dioxygen was investigated at low temperatures by means of UV/Vis spectroscopy. The reaction products can be classified into ,-,2:,2 -peroxodicopper(II) or bis(,-oxo)dicopper(III) complex cations that contain the {Cu2O2}2+ core portion as different isomers. The electronic properties of the specific bis(guanidine) ligands are discussed from the viewpoint of their ,-donor and ,-acceptor capabilities, and it is shown that ,-,2:,2 -peroxodicopper(II) complexes are stabilised relative to the bis(,-oxo)dicopper(III) ones if , conjugation within the guanidine moieties is optimised. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Formation of molecular radical cations of aliphatic tripeptides from their complexes with CuII(12-crown-4)RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2004Ivan K. Chu Molecular radical cations have proven to be difficult to generate from aliphatic peptides under electrospray ionization mass spectrometry (ESI-MS) conditions. For a family of small aliphatic peptides GGX, where XG, A, P, I, L and V, these cations have been generated by electrospraying a mixture of Cu.2+, 12-crown-4 and GGX in methanol/water. GGX.+ is readily formed from the collision-induced dissociation (CID) of [CuII(12-crown-4)(GGX)].2+. The formation of these aliphatic peptide radical ions from these complexes, in cases where it is not possible from the corresponding complexes involving a series of amine ligands instead of 12-crown-4, is likely due to the second ionization energy of the [CuI(12-crown-4)(GGX)]+ complex being higher than that of the corresponding [CuI(amine)(GGX)]+ complex. Using these 12-crown-4 complexes, GGI can be differentiated from the isomeric GGL by comparing the CID spectra of their [a3+H].+ ions. Copyright © 2004 John Wiley & Sons, Ltd. [source] Behavioural dynamics in the biological control of pests: role of silicon complexesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 11 2008Savita Belwal Abstract The complexes of silicon (IV) with Schiff base ligands (L1H and L2H of isatin derivatives) having a sulfur and oxygen donor system were prepared by the reactions in methanol environment. These were isolated and characterized by elemental analysis, molecular weight determinations and conductance measurements. On the basis of electronic, infrared, 1H, 13C and 29Si NMR spectral studies, trigonal bipyramidal geometry was suggested for the resulting complexes. These data support preferential binding of sulfur and oxygen atom to the silicon atom. The disease resistance activities of the ligands and their corresponding complexes were examined successfully in in vitro and in vivo experiments, against pathogenic fungi and bacteria. Results were quite encouraging and these were compared with the standard pesticides Bavistin and Streptomycin. Copyright © 2008 John Wiley & Sons, Ltd. [source] Stabilisation of RNA Bulges by Oligonucleotide Complements Containing an Adenosine AnalogueCHEMBIOCHEM, Issue 11 2003Annemieke Madder Abstract Incorporation of 2,-deoxy-2,- , -(1-naphthylmethyl)tubercidin into an oligodeoxyribonucleotide mostly has little or a slightly negative effect on the Tmvalues of complexes with DNA complements. With the same naphthylmethyl-substituted nucleoside at the 3,-end of a 2,-O-methyloligoribonucleotide, however, a stabilisation of 1,2,°C in the corresponding complexes with both DNA and RNA is observed. When the target sequence is an RNA fragment forming a two- or three-nucleotide bulge, complexes with (naphthylmethyl)tubercidin-modified oligodeoxyribonucleotides, as well as with the corresponding 2,-O-methyloligoribonucleotides, give stabilisations of 1,2,°C for the three-nucleotide bulge and of almost 4,°C for the two-nucleotide bulge. This stabilisation is specific to RNA, since the corresponding complexes with the DNA fragments do not display this effect. Thus, the (naphthylmethyl)tubercidin-containing oligonucleotides are the first reported oligonucleotide modifications that specifically stabilise bulged RNA. [source] | ||||||||||