Home About us Contact
|
Home About us Contact | ||
|
|
||
Ligand Substitution (ligand + substitution)
Selected AbstractsReactivity and X-ray Structural Studies in Ligand Substitution of [Cp/(Ind)Ru(dppf)Cl] , Epimerisation in [Cp/(Ind)Ru(Josiphos)Cl] {Cp = ,5 -C5H5, Ind = ,5 -C7H9, dppf = 1,1,-Bis(diphenylphosphanyl)ferrocene, Josiphos = (R)-(,)-1-[(S)-2-(Diphenylphosphanyl)ferrocenyl]ethyldicyclohexylphosphane}EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2007Sin Yee Ng Abstract Ligand substitution of [(Ind)Ru(PPh3)2Cl] (1) led to the isolation of [(Ind)Ru(PPh3){Ph2P(CH2)2C9H7}Cl] (2), [(Ind)Ru(dppf)Cl] (3) and [(Ind)Ru{(Ph2PCH2)3CMe}]PF6 ([4]PF6), and diastereoisomers [(R)- and (S)-(Ind)Ru(Josiphos)Cl] [(R)- 5 and (S)- 5], where (R)-(S)-Josiphos is the ferrocene-based chiral diphosphane ligand (R)-(,)-1-[(S)-2-(diphenylphosphanyl)ferrocenyl] ethyldicyclohexylphosphane. The Cp analogues of 5, viz. (R)- 6 and (S)- 6, were also obtained from [CpRu(PPh3)2Cl] (1a). Josiphos-dependent epimerisation was observed, with conversion of the (S) isomer to the (R) isomer in both cases. Chloride abstraction of 3 with NaPF6 in CH3CN and NaN3 in EtOH gave [(Ind)Ru(dppf)(CH3CN)]PF6 ([7]PF6) and [(Ind)Ru(dppf)(N3)] (8), respectively. The azido ligand in 8 underwent [3+2] dipolar cycloaddition with dimethyl acetylenedicarboxylate to give a N -bound bis(methoxycarbonyl)-1,2,3-triazolato complex, 9. X-ray crystal structures of the new complexes, except (R)- 5, (S)- 5 and (S)- 6, have been determined. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Cationic Brønsted Acids for the Preparation of SnIV Salts: Synthesis and Characterisation of [Ph3Sn(OEt2)][H2N{B(C6F5)3}2],[Sn(NMe2)3(HNMe2)2][B(C6F5)4] and [Me3Sn(HNMe2)2][B(C6F5)4]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2006Yann Sarazin Abstract Ph3SnN(SiMe3)2 (1) was prepared in good yields by reaction of [{NaN(SiMe3)2}2·THF] (2) with Ph3SnF. Treatment of 1 with [H(OEt2)2][H2N{B(C6F5)3}2] (4) in dichloromethane afforded the stannylium cation [Ph3Sn(OEt2)][H2N{B(C6F5)3}2] (5), which was characterised by 1H, 13C{1H}, 11B, 19F and 119Sn NMR spectroscopy. The reaction of Sn(NMe2)4 with [Ph2MeNH][B(C6F5)4] (3) gave the amidotin(IV) compound [Sn(NMe2)3(HNMe2)2][B(C6F5)4] (6) which proved very stable towards ligand substitution and resisted treatment with Et2O, THF, TMEDA and pyrazine. Two new Brønsted acid salts [H(NMe2H)2][B(C6F5)4] (7) and [(C4H4N2)H·OEt2][H2N{B(C6F5)3}2] (8) were synthesised. The reaction of 7 with Sn(NMe2)4 in Et2O allowed the preparation of 6 in a much improved yield (83,%). The treatment of 7 with Me3SnN(SiMe3)2 in Et2O yielded [Me3Sn(HNMe2)2][B(C6F5)4] (9) nearly quantitatively. Compounds 1, 2, 6, 8 and 9 were characterised by single-crystal X-ray diffraction analyses; 6 is the first example of a structurally characterised amidotin(IV)cation.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Stable Nickel Catalysts for Fast Norbornene Polymerization: Tuning ReactivityEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2005Juan A. Casares Abstract The air-stable complexes trans -[Ni(C6Cl2F3)2L2] (L = SbPh3, 1; AsPh3, 2; AsCyPh2, 3; AsMePh2, 4; PPh3, 5) have been synthesized by arylation of [NiBr2(dme)] (dme = 1,2-dimethoxyethane) in the presence of the corresponding ligand L (for compounds 1,4) or by ligand substitution starting from 1 (for compound 5). The structures of 1, 2, and 5 have been determined by X-ray diffraction and show an almost perfect square-planar geometry in all cases. Their catalytic activity in insertion polymerization of norbornene have been tested showing a strong dependence of the yield and molecular mass of the polymer on the ligand used and the solvent. High yield and high molecular mass values are obtained using complexes with ligands easy to displace from NiII (SbPh3 is the best) and noncoordinating solvents. Complexes 1,3 are suggested as convenient bench-catalysts to have available in the lab. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] The Reaction of (Bipyridyl)palladium(II) Complexes with Thiourea , Influence of DNA and Other Polyanions on the Rate of ReactionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2005Matteo Cusumano Abstract [Pd(bipy)(py)2](PF6)2 reacts stepwise with excess thiourea to give [Pd(tu)4](PF6)2. The kinetics of the second step, which refers to the replacement of bipyridyl in [Pd(bipy)(tu)2](PF6)2, have been studied in water and in the presence of calf thymus DNA, sodium polyriboadenylate, sodium polyvinylsulfonate or sodium polymetaphosphate at 25 °C and pH = 7 and a fixed sodium chloride concentration. The reaction follows a first order course and a plot of kobs against [thiourea]2 affords a straight line with a small intercept. DNA inhibits the process without altering the rate law. The kobs values decrease systematically on increasing the DNA concentration eventually tending to a limiting value. The values are larger at higher ionic strengths and the other polyanions show similar behaviour. The influence of DNA on the kinetics can be related to steric inhibition caused by noncovalent binding with the complex. Upon interaction with DNA, [Pd(bipy)(tu)2]2+ gives rise to immediate spectroscopic changes in the UV/Vis region as well as induced circular dichroism suggesting that the complex, like similar platinum(II) and palladium(II) species of bipyridyl, intercalates with the double helix. Such a type of interaction hampers the attack of the nucleophile at the metal centre inhibiting the reaction. The decrease in the rate of ligand substitution upon decreasing salt concentration but at a given DNA concentration is due to the influence of ionic strength on the complex,DNA interaction. The reactivity inhibition by single-stranded poly(A), polyvinylsulfonate or polymetaphosphate can be accounted for in terms of self-aggregation of the complex induced by the polyanion. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Water Stability and Luminescence of Lanthanide Complexes of Tripodal Ligands Derived from 1,4,7-Triazacyclononane: Pyridinecarboxamide versus Pyridinecarboxylate DonorsHELVETICA CHIMICA ACTA, Issue 11 2009Grégory Nocton Abstract A series of europium(III) and terbium(III) complexes of three 1,4,7-triazacyclononane-based pyridine containing ligands were synthesized. The three ligands differ from each other in the substitution of the pyridine pendant arm, namely they have a carboxylic acid, an ethylamide, or an ethyl ester substituent, i.e., these ligands are 6,6,,6,-[1,4,7-triazacyclononane-1,4,7-triyltris(methylene)]tris[pyridine-2-carboxylic acid] (H3tpatcn), -tris[pyridine-2-carboxamide] (tpatcnam), and -tris[pyridine-2-carboxylic acid] triethyl ester (tpatcnes) respectively. The quantum yields of both the europium(III) and terbium(III) emission, upon ligand excitation, were highly dependent upon ligand substitution, with a ca. 50-fold decrease for the carboxamide derivative in comparison to the picolinic acid (=pyridine-2-carboxylic acid) based ligand. Detailed analysis of the radiative rate constants and the energy of the triplet states for the three ligand systems revealed a less efficient energy transfer for the carboxamide-based systems. The stability of the three ligand systems in H2O was investigated. Although hydrolysis of the ethyl ester occurred in H2O for the [Ln(tpatcnes)](OTf)3 complexes, the tripositive [Ln(tpatcnam)](OTf)3 complexes and the neutral [Ln(tpatcn)] complexes showed high stability in H2O which makes them suitable for application in biological media. The [Tb(tpatcn)] complex formed easily in H2O and was thermodynamically stable at physiological pH (pTb 14.9), whereas the [Ln(tpatcnam)](OTf)3 complexes showed a very high kinetic stability in H2O, and once prepared in organic solvents, remained undissociated in H2O. [source] Mechanistic Studies of Metal Aqua Ions: A Semi-Historical PerspectiveHELVETICA CHIMICA ACTA, Issue 3 2005Stephen A semi-historical review of the establishment of the nature of metal aqua ions ranging from the alkali metal ions to the lanthanides and the mechanism of water exchange and ligand substitution on them is presented. [source] On the use of "fast kinetics" to determine the mechanism of ligand substitution at a solvated transition-metal intermediateINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2004Richard H. Schultz Substitution of the weakly-coordinated solvent molecule at a solvated transition-metal intermediate is frequently investigated by "fast kinetic" methods. In typical experiments, the kinetics of the reaction are determined by following the time dependence of the changes in the reaction mixture's UV-visible or infrared spectrum following photolytic creation of the intermediate. We consider the two limiting mechanisms (associative and dissociative), as well as the case of competition between them, and show that under typical "fast kinetics" experimental conditions, the different mechanisms are kinetically indistinguishable. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 427,433, 2004 [source] Osmabenzenes from Osmacycles Containing an ,2 -Coordinated OlefinCHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2009Lei Gong Dr. Abstract Osmabenzenes can be easily synthesized from two ,2 -coordinated olefin osmacycles in the presence of benzonitrile by means of facile hydrogen-transfer conversions (see graphic). Mechanisms for the formation of osmabenzenes are proposed based on DFT calculations. Treatment of HCCC(CH3)(OH)CHCH2 with [OsCl2(PPh3)3] in dichloromethane yielded the ,2 -olefin-coordinated osmacycle [Os{CHC(PPh3)C(CH2)-,2 -CHCH2}Cl2(PPh3)2] (9). Transformations of osmacycle 9 by treatment with benzonitrile under various conditions have been investigated. Reaction of 9 with excess benzonitrile at room temperature afforded the dicationic osmacycle [Os{CHC(PPh3)C(CH2)-,2 -CHCH2}(PhCN)2(PPh3)2]Cl2 (11) by ligand substitution, which reacted further to the intramolecularly coordinated ,2 -allene complex [Os{CHC(PPh3)C(CH3)(,2 -CCH2)}(PhCN)2(PPh3)2]Cl2 (12). In contrast, heating a chloroform solution of 9 to the reflux temperature in the presence of excess benzonitrile generated osmabenzene [Os{CHC(PPh3)C(CH3)CHCH}(PhCN)2(PPh3)2]Cl2 (14). Complexes 11, 12 and 14 are in fact isomers. In the absence of excess benzonitrile, the isolated dicationic 12 and 14 readily dissociate the benzonitrile ligands in solution to produce the neutral complex [Os{CHC(PPh3)C(CH3)(,2 -CCH2)}Cl2(PPh3)2] (13) and the monocationic osmabenzene [Os{CHC(PPh3)C(CH3)CHCH}Cl(PhCN)(PPh3)2]BPh4 (15), respectively. Mechanisms for the formation of osmabenzene 14 from 11 and 12 are proposed based on DFT calculations. [source] | ||||||||||