Metal coordination

Metal coordination (method Q) Reaction of triphenylbismuthine with triamminechromium tricarbonyl in dioxane at 120°C leads to a mixture of chromium tricarbonyl ir-complexes of triphenylbismuthine [81IZV1874], Extraction and recrystallization permit separation of three types of bismuthine. 

A mixture of triphenylbismuthine (4.4 g, 10 mmol), triamminechromium tricarbonyl (5.7 g, 30 mmol), and dioxane (40 ml) was heated with stirring for 7 h. After separation of the calculated amount of ammonia, the cooled mixture was filtered, the clear yellow solution was evaporated in vacuo, and the residue was treated with hot hexane. The solution was decanted and the residue was dried in vacuo. Extraction with hot cyclohexane yielded yellow crystals (0.73 g) soluble in benzene and acetone. After recrystallization from ethanol, I was obtained. Extraction with hot benzene of a portion of the product, after the separation of I, yielded a yellow compound (3.05 g), which was recrystallized from benzene to give II. Recrystallization of the residue from dioxane gave III (2.62 g) [81IZV1874]. 

After assembly around Cu(I), the terminal hydroxyl groups of the phenyl substituents of each 2,9-diphenyl-l,10-phenanthroline were joined by a Williamson 

SCHEME 17.1 Metal-assisted template synthesis of a [2]catenane developed by Sauvage et al.  

The two terminal hydroxyl groups on the strand of the open-knot zinc complex were connected with 3,6,9-trioxaundecanedioic acid using EDCI coupling in an esterification reaction under high dilution conditions to afford the knot in 25% 

SCH EME 17.2 Tris-bidentate ligand developed by Hunter et al and x-ray crystal structure. H atoms are omitted for clarity. Redrawn from CCDC163073) of its Zn complex obtained by metal templation and forming a trefoil knot. 

The intent of metal coordination is to provide both a robust tanplate platform and a large diversity of stereochonical geometries defined by the coordination properties of the metal. In addition to tetrahedral and octahedral coordination geometries obtained, for example, with Cu(I) or Zn(II), respectively, linear arrangements can be obtained using Au(I) centers coordinated to alkyne- and phosphine-terminated strands to prepare different types of catenates. 2 Square planar coordination around Pd(II) was also used to generate a doubly interlocked [2]catenane, known as a Solomon link.  

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MOMEC is a force field for describing transition metal coordination compounds. It was originally parameterized to use four valence terms, but not an electrostatic term. The metal-ligand interactions consist of a bond-stretch term only. The coordination sphere is maintained by nonbond interactions between ligands. MOMEC generally works reasonably well for octahedrally coordinated compounds. 

PC Model has some features that are not found in many other molecular mechanics programs. This is one of the few programs that outputs the energy given by the force field and the heat of formation and a strain energy. Atom types for describing transition structures in the MMX force field are included. There is a metal coordination option for setting up calculations with metal atoms. There are also molecular similarity and conformation search functions. 

In addition to the processes mentioned above, there are also ongoing efforts to synthesize formamide direcdy from carbon dioxide [124-38-9J, hydrogen [1333-74-0] and ammonia [7664-41-7] (29—32). Catalysts that have been proposed are Group VIII transition-metal coordination compounds. Under moderate reaction conditions, ie, 100—180°C, 1—10 MPa (10—100 bar), turnovers of up to 1000 mole formamide per mole catalyst have been achieved. However, since expensive noble metal catalysts are needed, further work is required prior to the technical realization of an industrial process for formamide synthesis based on carbon dioxide. 

The metal coordination complexes of both sahcylaldehyde phenyhiydrazone (91) and sahcylaldoxime provide antioxidant (92) protection and uv stabihty to polyolefins (see Antioxidants). In addition, the imines resulting from the reaction of sahcylaldehyde and aromatic amines, eg, p- am in oph en o1 or a-naphthylamine, can be used at very low levels as heat stabiLizers (qv) in polyolefins (93). 

The triply connected phosphoms compounds have a lone electron pair that dominates much of the chemistry for these compounds. Triply connected compounds typically exhibit pyramidal symmetry arising fromp hybridization. A considerable amount of sp character may be present as well. Bond angles range near 100° vs 90° theoretical. Tricoordinate compounds typically act as electron donors, forming metal coordination compounds and addition compounds such as H P BF [41593-56-0]. 

Although trialkyl- and triarylbismuthines are much weaker donors than the corresponding phosphoms, arsenic, and antimony compounds, they have nevertheless been employed to a considerable extent as ligands in transition metal complexes. The metals coordinated to the bismuth in these complexes include chromium (72—77), cobalt (78,79), iridium (80), iron (77,81,82), manganese (83,84), molybdenum (72,75—77,85—89), nickel (75,79,90,91), niobium (92), rhodium (93,94), silver (95—97), tungsten (72,75—77,87,89), uranium (98), and vanadium (99). The coordination compounds formed from tertiary bismuthines are less stable than those formed from tertiary phosphines, arsines, or stibines. 

In the absence of metal coordination the compound would titrate as a typical tetrabasic acid having a stepwise titration curve as shown in Figure 6. 

Fig. 1. Common geometries for metal coordination numbers from two through nine (see Table 1), where O represents the metal and O, a ligand donor...

Metal coordination compounds may also provide alternatives to the heterogeneous catalysts used for the water gas shift reaction. In fact, Ru, Rh, Ir, and Pt coordination compounds have all shown some promise (27). 

Dyes and Pigments. Several thousand metric tons of metallated or metal coordinated phthalocyanine dyes (10) are sold annually in the United States. The partially oxidized metallated phthalocyanine dyes are good conductors and are called molecular metals (see Semiconductors Phthalocyanine compounds Colorants forplastics). Azo dyes (qv) are also often metallated. The basic unit for a 2,2 -azobisphenol dye is shown as stmcture (11). Sulfonic acid groups are used to provide solubiHty, and a wide variety of other substituents influence color and stabiHty. Such complexes have also found appHcations as analytical indicators, pigments (qv), and paint additives. 

R. M. Baum, Chem. Eng Nem 70(22), 25—27, 30—33 (June 1, 1992). Reviews advances ia fuUerene chemistry including metal coordination, but without a tme bibHography. 

CSM products may be divided into three groups depending on the type of precursor resin low density (LDPE), high density (HDPE), and linear low density (LLDPE). LDPE is made by a high pressure free-radical process, while HDPE and LLDPE are made via low pressure, metal coordination catalyst processes (12) (see Olefin polymers). 

The most numerous cases of homogeneous catalysis are by certain ions or metal coordination compounds in aqueous solution and in biochemistry, where enzymes function catalyticaUy. Many ionic effects are known. The hydronium ion and the hydroxyl ion OH" cat-... 

Titanium tetrachloride and tin tetrachloride can form complexes that are related in character to both those formed by metal ions and those formed by neutral Lewis acids. Complexation can occur with an increase in the coordination number at the Lewis acid or with displacement of a chloride from the metal coordination sphere. 

A very significant recent development in the field of catalytic hydrogenation has been the discovery that certain transition metal coordination complexes catalyze the hydrogenation of olefinic and acetylenic bonds in homogeneous solution.Of these catalysts tris-(triphenylphosphine)-chloror-hodium (131) has been studied most extensively.The mechanism of the deuteration of olefins with this catalyst is indicated by the following scheme (131 -> 135) ... 

VI. Stabilization of Unusual Tautomeric Forms of Azoles and Their Derivatives in Metal Coordination Compounds... 

Due to the relatively high acidities of their hydroxy groups, hydroxyazoles readily exchange their protons with metal ions, which leads to stabilization of metal derivatives of the hydroxy tautomeric forms in metal coordination compounds of 2(5)-oxoazoles [97UK434 98AHC(72)1]. A typical example is the mercury complex 361 [93JCS(D)1003]. 

The complex 23 is the first X-ray structurally characterized metal coordination compound with a benzochalcogenazole ligand in which chalcogen behaves as the ligating atom. 

Chloroaluminate(III) ionic liquid systems are perhaps the best established and have been most extensively studied in the development of low-melting organic ionic liquids with particular emphasis on electrochemical and electrodeposition applications, transition metal coordination chemistry, and in applications as liquid Lewis acid catalysts in organic synthesis. Variable and tunable acidity, from basic through neutral to acidic, allows for some very subtle changes in transition metal coordination chemistry. The melting points of [EMIM]C1/A1C13 mixtures can be as low as -90 °C, and the upper liquid limit almost 300 °C [4, 6]. 

Transition metal catalysis in liquid/liquid biphasic systems principally requires sufficient solubility and immobilization of the catalysts in the IL phase relative to the extraction phase. Solubilization of metal ions in ILs can be separated into processes, involving the dissolution of simple metal salts (often through coordination with anions from the ionic liquid) and the dissolution of metal coordination complexes, in which the metal coordination sphere remains intact. 

Compared with other metal coordination compounds, relatively little is known about chelate photochemistry. 

In contrast to 1, isomeric p-nitrophenyl nicotinate shows almost no catalysis. Thus, it is clear that substrate coordination to the metal ion complex plays the critical role for an enormous rate enhancement. The lipophilic ester (R = C5Hn) also undergoes a large rate enhancement indicating the importance of substrate binding into the micellar phase by hydrophobic interaction. A large rate enhancement can also be seen in lipophilic esters which lack the metal coordination site as given below with the enantioselective micellar reactions (Table 9, 10). 

The active form of a Ziegler-Natta catalyst is an alkyltitanium intermediate with a vacant coordination site on the metal. Coordination of alkene monomer... 

Reduction of X Me from 8 to 6 leads to a reduction of the metal coordination number from 8 to 6, respectively, and to the formation of octahedrons (distorted octahedrons) as a basic unit. 

Unsubstituted phthalocyanines are accessible by the reaction of phthalonitrile with metals, alloys, metal salts or metal coordination compounds. Often a mixture of these compounds and phthalonitrile are heated without solvent beyond the melting point of phthalonitrile. 

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