Acetonitrile metal complexes

Acetonitrile also is used as a catalyst and as an ingredient in transition-metal complex catalysts (35,36). There are many uses for it in the photographic industry and for the extraction and refining of copper and by-product ammonium sulfate (37—39). It also is used for dyeing textiles and in coating compositions (40,41). It is an effective stabilizer for chlorinated solvents, particularly in the presence of aluminum, and it has some appflcation in... 

Formation constants of metal complexes in non-aqueous solvents, I — acetonitrile. R. C. Kapoor and J. Kishan, Rev. Anal. Chem., 1981, S, 257-280 (96). 

Bradley et al.109 have combined a p-Si photocathode and homogeneous catalysts (tetraazamacrocyclic metal complexes, which had been shown to be effective catalysts for C02 reduction at an Hg electrode110) to reduce the applied cathode potential. The catalysts showed111 reversible cyclic voltammetric responses in acetonitrile at illuminated p-Si electrodes at potentials significantly more positive (ca. 0.4 V) than those required at a Pt electrode, where the p-Si used had surface states in high density and Fermi level pinning112 occurred. Electrolysis of a C02-saturated solution (acetonitrile-H20-LiC104 1 1 0.1 M) in the presence of 180 mM... 

Whether [6]radialenes have a potential as novel ligands for metal complexes remains to be seen. A first example of a successful complexation is provided by 150, which reacts with tris(acetonitrile)tricarbonylchromium in dioxane at room temperature to give the ortho-xylylene chromium complex 175 in excellent yield (83%) (equation 23)105. 

The first indication that such O-coordinated (phenoxyl)metal complexes are stable and amenable to investigation by spectroscopy was obtained when the electrochemistry of the colorless, diamagnetic complexes [Mm(LBu2)], [Mm(LBuMet)] (M = Ga, Sc) containing three coordinated phenolates in the cis-position relative to each other was investigated in acetonitrile solutions (142). A representative structure of [Scm(LBuMet)] is shown in Fig. 12. 

In the case of the [CuL]2+ complex discussed previously, it is likely that the positive value of AS°c (+ 133.2 J K l mol-1) might result as a consequence of the charge decrease that occurs on passing from [CuL]2+ to [CuL] +, which causes a release of solvent molecules (acetonitrile) towards the mass of the solution, i.e. part of those molecules which were ordered by the dipole interaction around the metal complex become disordered. 

The importance of solvent effects has been outlined in Section 2.2.1. An illustration with some of the fluoroionophores described in this section is given in Table 2.2. For alkali and alkaline-earth metal ions, the stability constants are higher in acetonitrile than in methanol these cations are indeed hard and have a stronger affinity for oxygen atoms (hard) than for nitrogen atoms (soft). In contrast, the soft silver atom has a strong affinity for nitrogen atoms and no complexation is observed in acetonitrile, whereas complexes in methanol, ether, and 1,2-dichloromethane are formed. 

Besides formaldehyde, Michael acceptors such as acrylonitrile and ethyl acrylate also serve as substrate to undergo the addition in the presence of various metal complexes [10-14]. Acrylonitrile affords P(CH2CH2CN)3 tcep (Scheme 3). The order of catalytic activity is reported to be Pt[P(CH2CH2CN)3]3>Pd[P(CH2CH2CN)3]3P IrCl[P(CH2CH2CN)3]3>Ni[P(C-H2CH2CN)3]3. The solvent effect on the rate is not significant. In acetonitrile, however, a small amount of a telomer is formed. 

Table I. Fluorescence Properties of Some Metal Complexes of TPP in Acetonitrile at 296 K...

Ionic liquids offer a highly polar but noncoordinating environment for chemistry. It is difficult to dissolve catalysts in nonpolar, noncoordinating molecular solvents such as hexane. Polar solvents, such as acetonitrile, tend to coordinate metal complexes. Ionic liquids such as the tetrafluoroborates offer a straightforward replacement of a solvent with a polar solvent that is noncoordinating. 

The free electron pair(s) in the concave pyridines 3 (Table 1), 13 (s. Scheme 3) and 29 (s. Scheme 5) and especially in the concave 1,10-phenanthrolines 11 (s. Scheme 2) and 21 (Structures 3) are not only able to bind a proton, they may also be used to coordinate a metal ion. For concave 1,10-phenanthrolines 11 and 21, transition metal complexes 87 (Structure 11) have already been generated [18, 55]. They form readily in acetonitrile solution with binding constants of 10 10 and larger. Of great importance is the nature of the chains X in the concave 1,10-phenanthrolines 21 (Structures 3). Pure aliphatic chains lead to smaller association constants than polyether chains. 

All C60 adducts have low-lying LUMOs that can easily be populated by electrochemical methods. For C60 itself, six reduction couples have been observed by cyclic voltammetry (CV) or square-wave voltammetry (SWV), and as many as four reduction couples have been found for many organometallics (9,84). Most of the studies have been performed in thf or acetonitrile at lower temperatures, which increases the size of the potential window. Table VII lists the half-wave potentials for some metal complexes, and Fig. 7 shows the cyclic voltammogram for [Co(NO)(PPh3)2(i72-C60)]. 

Many transition-metal complexes have been widely studied in their application as catalysts in alkene epoxidation. Nickel is unique in the respect that its simple soluble salts such as Ni(N03)2 6H20 are completely ineffective in the catalytic epoxidation of alkenes, whereas soluble manganese, iron, cobalt, or copper salts in acetonitrile catalyze the epoxidation of stilbene or substituted alkenes with iodosylbenzene as oxidant. However, the Ni(II) complexes of tetraaza macrocycles as well as other chelating ligands dramatically enhance the reactivity of epoxidation of olefins (90, 91). 

The neutral zinc complexes described in Figure 9.5 are proving to be quite remarkable compounds. Their preparation is simple and the synthetic yields are high (typically 70-90%). When one looks at the crude product, few if any side products are seen. Mechanical losses probably account for the less than perfect isolated yields obtained. The neutral metal complexes are typically freely soluble in various organic solvents (e.g., toluene, CH2CI2, CHClj, THF, dioxane, and acetonitrile) and partially soluble in methanol. They are generally insoluble in hexanes, diethyl ether or cold methanol, and these latter organic solvents can be used to precipitate the... 

Other metal complexes such as 2,2 -bipyridine complexes of Rh and Ir are efficient electrocatalysts for the reduction of C02 in acetonitrile.134 In the production of formate the current efficiency is up to 80%. Electrochemical reduction catalyzed by mono- and dinuclear Rh complexes affords formic acid in aqueous acetonitrile, or oxalate in the absence of water.135 The latter reaction, that is, the reduction of C02 directed toward C-C bond formation, has attracted great interest.131 An exceptional example136 is the use of metal-sulfide clusters of Ir and Co to catalyze selectively the electrochemical reduction of C02 to oxalate without the accompanying disproportionation to CO and CO2-. 

Cyclopentenes behave differently and often act through radical mechanisms this can lead to photoreduction to cyclopentanes, or photoaddition of the kind exemplified by norborneneand propan-2-ol 12.57). The photoadduct in this process is linked through the carbon atom of the alcohol, and not the oxygen atom. A related addition to acetonitrile 12.58) takes place when norbornene is irradiated in the presence of a silver(i) compound. It is likely thal a metal complex of the alkene is the real irradiation substrate, and the same may be true for copper(i)-promoted additions of haloalkanes to electron-deficient alkenes (2.59). When dichloromelhane is used in such a reaction the product can be reduced electrochemically to a cyclopropane (2.60), which is of value because the related thermal addition of CH.I, to alkenes in the presence of copper does not succeed with electron-poor compounds. 

Goewie et al. (19) developed an organometallic-silica bonded phase for the selective retention of phenylurea herbicides and anilines from water. Seven-micrometer diameter silica was derivatized with 2-amino-1-cyclopentene-l-dithiocarboxylic acid (ACDA), resulting in Structure I. Capacity factors of phenylurea herbicides and corresponding anilines were measured on the ACDA-silica and ACDA-metal-loaded silica. The platinum-loaded material was found to selectively retain the anilines. Anilines could be eluted with acetonitrile, but not with methanol or tetrahydrofuran, because of the strength with which acetonitrile forms complexes with platinum and thus displaces the anilines. Application of the ACDA-Pt precolumn in series with an ODS-silica precolumn for... 

The first metal complex of quinuclidine (2) was reported in 1966.58 Ag(quinuclidine)2N03 was isolated as a white solid after reaction of quinuclidine and silver nitrate in acetonitrile for several days. The formation constants were determined in DMSO (Table 11). The complex melted with decomposition at 158 °C. 

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