共查询到20条相似文献,搜索用时 15 毫秒
1.
V. V. Khrizanforova Yu. G. Budnikova I. D. Strelnik E. I. Musina M. I. Valitov M. K. Kadirov A. A. Karasik O. G. Sinyashin 《Russian Chemical Bulletin》2013,62(4):1003-1009
Nickel complexes with new cyclic ligands containing phosphorus and nitrogen atoms as coordination sites are novel efficient catalysts for hydrogen oxidation. A systematic study of their electrochemical properties made it possible to classify the nickel systems in question into four groups according to the sequence of electron transfer processes in the reduction (MII-MI-M0) and to the nature of solvents and counterions. Regularities of catalytic transformations involving nickel complexes with P,N-cyclic ligands in the H2 oxidation reaction in the coordination sphere of the catalyst and a correlation between the structure of the complex and its redox properties were established. The most efficient catalysts contain phenyl and 2-pyridyl substituents at the phosphorus atom and benzyl or 2-pyridyl substituents at the nitrogen atom. 相似文献
2.
《Tetrahedron: Asymmetry》2006,17(12):1759-1762
We describe the improved catalytic reactivity of terminal alkenes with 1,2-diboranes in the presence of Au(I) and Ag(I) complexes when N-heterocyclic carbene ligands are used. The new catalytic systems are able to diminish the undesired β-H-elimination of the alkylboryl–metal intermediates, which leads to the formation of hydroborated byproducts. The electronic properties and molecular the structure of the precursors of the catalysts could explain the modest asymmetric induction provided. 相似文献
3.
Yu. G. Budnikova A. G. Kafiyatullina Yu. M. Kargin O. G. Sinyashin 《Russian Chemical Bulletin》2003,52(7):1504-1511
Electrochemical reduction of cobalt(ii) complexes containing -acceptor ligands (L = bpy, Ph2Ppy) proceeds through three consecutive reversible steps: one-electron transfer to form a more stable CoIL complex, transfer of two electrons at more negative potentials to form an anionic [NiL]– complex, and reduction of the ligand to the radical anion. The stability of the cobalt complexes with different ligands decreases in the series Ph2Ppy > Ph3P > bpy. 相似文献
4.
《Journal of Coordination Chemistry》2012,65(15):2671-2682
Nickel salen and salophen complexes have been covalently anchored on multi-walled carbon nanotubes (MWNTs). The MWNT-supported nickel complexes have been characterized by inductive coupled plasma spectroscopy, FT-IR spectroscopy, UV-Vis spectrophotometry, transmission electron microscopy, and X-ray diffraction. The catalytic performance for the oxidation of primary and secondary alcohols was evaluated using periodic acid as oxidant. Reaction conditions have been optimized for MWNT-supported salen and salophen complexes by considering the effect of parameters such as solvent, reaction time, concentration of catalyst, amount of oxidant, etc. The catalytic activity was higher for supported catalysts than similar homogeneous ones. These supported catalysts were highly stable and reused several times without the loss of catalytic activity. 相似文献
5.
Sk Manirul Islam Manir Mobarok Paramita Mondal Anupam Singha Roy Noor Salam Dildar Hossain Sanchita Mondal 《Transition Metal Chemistry》2012,37(1):97-107
A tetradentate Schiff base (teta), obtained from triethylenetetramine and salicylaldehyde, has been covalently bonded to divinylbenzene
cross-linked chloromethylated polystyrene. This chelating ligand, abbreviated as PS-teta (PS = polymeric support), reacts
with metal chlorides (Cu2+, Co2+, and Ni2+) in methanol to give polymer-bound transition metal complexes, PS-Cu(II)teta/(Cat-1), PS-Ni(II)teta/(Cat-2), and PS-Co(II)teta/(Cat-3),
formation of which has been established by various physiochemical methods and spectroscopic techniques. The catalytic potential
of these materials has been tested for the oxidation of various alkenes, alkanes, alcohols, and thioethers in the presence
of 30% H2O2 as an oxidant. At the same time, these catalysts are very stable and could be reused in oxidation reactions for more than
five times without noticeable loss of their catalytic activity. 相似文献
6.
Dinuclear copper(II) complexes (Cu2 LnCl3), nickel(II) complexes (Ni2 LnCl3) and cobalt(II) complexes (Co2L
2
n
Cl2) from Schiff base ligands are synthesised, characterised and used as catalysts for oxidation of 3,5-DTBC to 3,5-DTBQ. (Cu2LnCl3) are found to be more efficient than the other complexes. Dinuclear iron(III) complexes of composition (Fe2L2Cl2) and ruthenium (III) complexes of composition Ru2L
2
n
Cl6(PPh3)2 and Ru2L
2
n
Cl2(PPh3)2 catalyse epoxidation of styrene and cyclohexene. Catalytic activities of ruthenium(III) complexes are much greater than those
of analogous iron(III) complexes. 相似文献
7.
Ledoux N Allaert B Pattyn S Vander Mierde H Vercaemst C Verpoort F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(17):4654-4661
Various symmetrically and asymmetrically substituted N-heterocyclic carbene (NHC) ligands bearing aliphatic nitrogen-containing side groups have been synthesised. In our attempts to isolate the corresponding second-generation Grubbs catalysts, we were unsuccessful when using the symmetrical aliphatic NHC ligands. For the asymmetrical ligands bearing an aliphatic moiety on one side and an aromatic mesityl group on the other side, substitution of a phosphine ligand was achieved. The performance of a so-formed series of Ru-based metathesis initiators has been evaluated for the ring-opening metathesis polymerisation (ROMP) of cycloocta-1,5-diene and the ring-closing metathesis (RCM) of diethyl diallylmalonate. 相似文献
8.
Iridium N-heterocyclic carbene complexes as efficient catalysts for magnetization transfer from para-hydrogen 总被引:1,自引:0,他引:1
Cowley MJ Adams RW Atkinson KD Cockett MC Duckett SB Green GG Lohman JA Kerssebaum R Kilgour D Mewis RE 《Journal of the American Chemical Society》2011,133(16):6134-6137
While the characterization of materials by NMR is hugely important in the physical and biological sciences, it also plays a vital role in medical imaging. This success is all the more impressive because of the inherently low sensitivity of the method. We establish here that [Ir(H)(2)(IMes)(py)(3)]Cl undergoes both pyridine (py) loss as well as the reductive elimination of H(2). These reversible processes bring para-H(2) and py into contact in a magnetically coupled environment, delivering an 8100-fold increase in (1)H NMR signal strength relative to non-hyperpolarized py at 3 T. An apparatus that facilitates signal averaging has been built to demonstrate that the efficiency of this process is controlled by the strength of the magnetic field experienced by the complex during the magnetization transfer step. Thermodynamic and kinetic data combined with DFT calculations reveal the involvement of [Ir(H)(2)(η(2)-H(2))(IMes)(py)(2)](+), an unlikely yet key intermediate in the reaction. Deuterium labeling yields an additional 60% improvement in signal, an observation that offers insight into strategies for optimizing this approach. 相似文献
9.
Pearly Sebastian Chittilappilly N. Sridevi K. K. Mohammed Yusuff 《Journal of molecular catalysis. A, Chemical》2008,286(1-2):92-97
Zeolite Y-encapsulated ruthenium(III) complexes of Schiff bases derived from 3-hydroxyquinoxaline-2-carboxaldehyde and 1,2-phenylenediamine, 2-aminophenol, or 2-aminobenzimidazole (RuYqpd, RuYqap and RuYqab, respectively) and the Schiff bases derived from salicylaldehyde and 1,2-phenylenediamine, 2-aminophenol, or 2-aminobenzimidazole (RuYsalpd, RuYsalap and RuYsalab, respectively) have been prepared and characterized. These complexes, except RuYqpd, catalyze catechol oxidation by H2O2 selectively to 1,2,4-trihydroxybenzene. RuYqpd is inactive. A comparative study of the initial rates and percentage conversion of the reaction was done in all cases. Turn over frequency of the catalysts was also calculated. The catalytic activity of the complexes is in the order RuYqap > RuYqab for quinoxaline-based complexes and RuYsalap > RuYsalpd > RuYsalab for salicylidene-based complexes. The reaction is believed to proceed through the formation of a Ru(V) species. 相似文献
10.
Khurshid A. Zafar M. N. Javed K. Iqbal N. Arshad M. N. 《Russian Chemical Bulletin》2020,69(11):2121-2128
Russian Chemical Bulletin - A nickel(II) complex with the newly synthesized dicarboxamide ligand [H2LBZ][(CF3SO3)Cl] was explored as a water oxidation catalysis. All the synthesized compounds were... 相似文献
11.
The preparation of a series of complexes of the type CpIrX2(NHC) provides effective catalysts for the H/D exchange of a wide range of organic molecules in methanol-d4. The reaction proceeds with higher yields under milder reaction conditions than previous CpIr systems reported thus far. For comparative purposes, we also studied the catalytic activity of CpIrCl2(PMe3) under the same reaction conditions. The molecular structures of two of the new CpIr(NHC) complexes are described. 相似文献
12.
Kantchev EA O'Brien CJ Organ MG 《Angewandte Chemie (International ed. in English)》2007,46(16):2768-2813
Palladium-catalyzed C-C and C-N bond-forming reactions are among the most versatile and powerful synthetic methods. For the last 15 years, N-heterocyclic carbenes (NHCs) have enjoyed increasing popularity as ligands in Pd-mediated cross-coupling and related transformations because of their superior performance compared to the more traditional tertiary phosphanes. The strong sigma-electron-donating ability of NHCs renders oxidative insertion even in challenging substrates facile, while their steric bulk and particular topology is responsible for fast reductive elimination. The strong Pd-NHC bonds contribute to the high stability of the active species, even at low ligand/Pd ratios and high temperatures. With a number of commercially available, stable, user-friendly, and powerful NHC-Pd precatalysts, the goal of a universal cross-coupling catalyst is within reach. This Review discusses the basics of Pd-NHC chemistry to understand the peculiarities of these catalysts and then gives a critical discussion on their application in C-C and C-N cross-coupling as well as carbopalladation reactions. 相似文献
13.
U. Klabunde R. Mulhaupt T. Herskovitz A. H. Janowicz J. Calabrese S. D. Ittel 《Journal of polymer science. Part A, Polymer chemistry》1987,25(7):1989-2003
Abstraction of phosphine from the nickel(II) P, O-chelated complexes, Ni[Ph2PCH?C(Ph)O] (Ph)(PPh3), and related species converts them from olefin oligomerization to olefin polymerization catalysts. Phosphine acceptors such as Rh(acetylacetonate)(C2H4)2 or Ni(1,5-cyclooctadiene)2 are most effective. Alternatively, nickel complexes in which the phosphine ligand is replaced with weakly coordinated pyridine can be prepared. These active, homogeneous catalysts can be tuned to give either low or high molecular weight, linear low or high density polyethylene. Depending on the diluent, the same catalytic complex can be used as heterogeneous or homogeneous catalyst. They are tolerant of oxygenated, hydroxylic, or polar molecules that would poison normal early transition metal-based Ziegler-Natta catalysts. In fact, the polymerizations can be run in solvents such as ethanol or acetone, but hydrocarbon solvents are preferred. 相似文献
14.
Bruijnincx PC Buurmans IL Gosiewska S Moelands MA Lutz M Spek AL van Koten G Klein Gebbink RJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(4):1228-1237
The Rieske dioxygenases are a group of non-heme iron enzymes, which catalyze the stereospecific cis-dihydroxylation of its substrates. Herein, we report the iron(II) coordination chemistry of the ligands 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its neutral propyl ester analogue propyl 3,3-bis(1-methylimidazol-2-yl)propionate (PrL1). The molecular structures of two iron(II) complexes with PrL1 were determined and two different coordination modes of the ligand were observed. In [Fe(II)(PrL1)(2)](BPh(4))(2) (3) the ligand is facially coordinated to the metal with an N,N,O donor set, whereas in [Fe(II)(PrL1)(2)(MeOH)(2)](OTf)(2) (4) a bidentate N,N binding mode is found. In 4, the solvent molecules are in a cis arrangement with respect to each other. Complex 4 is a close structural mimic of the crystallographically characterized non-heme iron(II) enzyme apocarotenoid-15-15'-oxygenase (APO). The mechanistic features of APO are thought to be similar to those of the Rieske oxygenases, the original inspiration for this work. The non-heme iron complexes [Fe(II)(PrL1)(2)](OTf)(2) (2) and [Fe(II)(PrL1)(2)](BPh(4))(2) (3) were tested in olefin oxidation reactions with H(2)O(2) as the terminal oxidant. Whereas 2 was an active catalyst and both epoxide and cis-dihydroxylation products were observed, 3 showed negligible activity under the same conditions, illustrating the importance of the anion in the reaction. 相似文献
15.
Tungsten complex with a coordinated 2-azidoethyl isocyanide ligand reacts with PMe3 at the azido function to give a complex with a coordinated iminophosphorane which upon hydrolysis of the P=N bond yields a complex with an NH,NH-stabilized N-heterocyclic carbene ligand, 7; alkylation of the carbene ring nitrogen atoms gives a complex with an N,N'-dialkylated imidazolidin-2-ylidene ligand, 8 . 相似文献
16.
Lee CC Ke WC Chan KT Lai CL Hu CH Lee HM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(2):582-591
Nickel(II) complexes of bidentate N-heterocyclic carbene (NHC)/phosphane ligand L were prepared and structurally characterized. Unlike palladium, which forms [PdCl(2)(L)], the stable nickel product isolated is the ionic [Ni(L)(2)]Cl(2). These Ni(II) complexes are highly robust in air. Among different N-substituents on the ligand framework, the nickel complex of ligand L bearing N-1-naphthylmethyl groups (2 a) is a highly effective catalyst for Suzuki cross-coupling between phenylboronic acid and a range of aryl halides, including unreactive aryl chlorides. The activities of 2 a are largely superior to those of other reported nickel NHC complexes and their palladium counterparts. Unlike the previously reported [NiCl(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane), 2 a can effectively catalyze the cross-coupling reaction without the need for a catalytic amount of PPh(3), and this suggests that the PPh(2) functionality of hybrid NHC ligand L can partially take on the role of free PPh(3). However, for unreactive aryl chlorides at low catalyst loading, the presence of PPh(3) accelerates the reaction. 相似文献
17.
N-heterocyclic carbenes (NHCs) are shown to be reasonable mimics of imidazole ligands in dinitrosyl iron complexes determined through the synthesis and characterization of a series of {Fe(NO)(2)}(10) and {Fe(NO)(2)}(9) (Enemark-Feltham notation) complexes. Monocarbene complexes (NHC-iPr)(CO)Fe(NO)(2) (1) and (NHC-Me)(CO)Fe(NO)(2) (2) (NHC-iPr = 1,3-diisopropylimidazol-2-ylidene and NHC-Me = 1,3-dimethylimidazol-2-ylidene) are formed from CO/L exchange with Fe(CO)(2)(NO)(2). An additional equivalent of NHC results in the bis-carbene complexes (NHC-iPr)(2)Fe(NO)(2) (3) and (NHC-Me)(2)Fe(NO)(2) (4), which can be oxidized to form the {Fe(NO)(2)}(9) bis-carbene complexes 3(+) and 4(+). Treatment of complexes 1 and 2 with [NO]BF(4) results in the formation of uncommon trinitrosyl iron complexes, (NHC-iPr)Fe(NO)(3)(+) (5(+)) and (NHC-Me)Fe(NO)(3)(+) (6(+)), respectively. Cleavage of the Roussin's Red "ester" (μ-SPh)(2)[Fe(NO)(2)](2) with either NHC or imidazole results in the formation of (NHC-iPr)(PhS)Fe(NO)(2) (7) and (Imid-iPr)(PhS)Fe(NO)(2) (10) (Imid-iPr = 2-isopropylimidazole). The solid-state molecular structures of complexes 1, 2, 3, 4, 5(+), and 7 show that they all have pseudotetrahedral geometry. Infrared spectroscopic data suggest that NHCs are slightly better electron donors than imidazoles; electrochemical data are also consistent with what is expected for typical donor/acceptor abilities of the spectator ligands bound to the Fe(NO)(2) unit. Although the monoimidazole complex (Imid-iPr)(CO)Fe(NO)(2) (8) was observed via IR spectroscopy, attempts to isolate this complex resulted in the formation of a tetrameric {Fe(NO)(2)}(9) species, [(Imid-iPr)Fe(NO)(2)](4) (9), a molecular square analogous to the unsubstituted imidazole reported by Li and Wang et al. Preliminary NO-transfer studies demonstrate that the {Fe(NO)(2)}(9) bis-carbene complexes can serve as a source of NO to a target complex, whereas the {Fe(NO)(2)}(10) bis-carbenes are unreactive in the presence of a NO-trapping agent. 相似文献
18.
Hydrotalcites (HTs) in variable Mg/Al ratios were used as catalysts for the Baeyer-Villiger (BV) oxidation of cyclic ketones with hydrogen peroxide. All HTs studied were found to be active in the BV oxidation of cyclohexanone, their activity increases with increasing Mg/Al ratio. The reaction, which was conducted under very mild conditions (viz. atmospheric pressure and a temperature of 70 °C), provided conversions above 70% with 100% selectivity only after 6 h. This outcome was found to require the presence of a nitrile in the reaction medium, so a mechanism involving adsorption of the nitrile and cyclohexanone onto the catalyst is proposed that is consistent with the experimental results. Based on the proposed mechanism, the presence of a surfactant should result in improved conversion and catalytic activity, as was indeed observed with sodium dodecylsulfate in the reaction medium. The best catalyst among those tested was used with other cyclic ketones and found to provide excellent conversion and selectivity results in most cases. 相似文献
19.
Shibata T Ito S Doe M Tanaka R Hashimoto H Kinoshita I Yano S Nishioka T 《Dalton transactions (Cambridge, England : 2003)》2011,40(25):6778-6784
Nickel complexes having acetylated glucopyranosyl group incorporated N-heterocyclic carbene (NHC) ligands with methyl or benzyl groups as an N-substituent exhibit two kinds of dynamic behaviours in solution (1)H NMR spectroscopy. One of the dynamic behaviours is attributed to the anti- and syn-rotamers, which occur by the rotation of the unsymmetrical NHC ligands around the axes of the Ni-C bonds. The other is attributed to the diastereomers of the syn-rotamers, which occur by opposite rotation of the imidazolylidene rings and the chiral carbohydrate group incorporated into the NHC ligands. Crystallographic analysis of the nickel complex having the NHC ligand with acetylated glucopyranosyl and benzyl groups as N-substituents showed CH-π interaction between the glucopyranosyl unit of each NHC ligand and the phenyl ring of the other NHC ligand in the complex in the solid state. 相似文献
20.
Rafael Llamas César Jiménez-Sanchidrián José Rafael Ruiz 《Reaction Kinetics and Catalysis Letters》2007,90(2):309-313
This paper reports the results obtained in the Baeyer-Villiger oxidation of cyclohexanone with a hydrogen peroxide/benzonitrile
mixture as oxidant in the presence of synthetic metal hydroxides or their calcined products as catalysts. The metal hydroxides
were obtained by coprecipitation. The best ε-caprolactone conversion results were provided by magnesium hydroxide. 相似文献