Sandwich compounds, preparation

Metal borohydrides, in hydroborations, 9, 158 Metal—borole sandwich compounds, preparation, 3, 3—5 Metal—borollide sandwich compounds, preparation, 3, 3—5 Metal carbenes... 

The title complexes are the first well-characterized multiiron sandwich compounds prepared via rational synthesis from lacunary or defect species. They have possible applications as catalysts for the oxidation of organic compounds with the environmentally friendly oxidant H202 and constitute a well-defined multiiron species to facilitate the further investigation and delineation of magnetic interactions in such systems." ... 

TThe x-ray stmcture of the novel bis-dicarboUide sandwich compound i (9y y (9-3,3 -Si(3,l,2-SiC2B2H22)2 contains a siUcon atom iu a highly unusual bonding mode (245). TThis compound, which is quite stable thermally, is prepared iu good yield. 

The sandwich compounds, feiTocene and nickelocene, FefCg 115)2 and Ni(C5H5)2, so called because die metal atom is sandwiched between the organic radicals, C5H5, have also been used to prepare iron and nickel deposits. 

At about 159°C it turns pink and adopts the sandwich structure, expected for [M(C5H5)2] compounds, and this is retained in the gaseous phase and in hydrocarbon solutions. Using substituted cyclopentadienyls a variety of analagous sandwich compounds have been prepared and their magnetic properties indicate that the... 

Many research compounds are poorly soluble in water. When very lipophilic molecules precipitate in the donor wells, it is possible to filter the donor solution before the PAMPA sandwich is prepared. On occasion, the filtered donor solution contains such small amounts of the compound that determination of concentrations by UV spectrophotometry becomes impractical. One strategy to overcome the precipitation of the sample molecules in the donor wells is to add a cosolvent to the solutions (Section 7.4.4). It is a strategy of compromise and practicality. Although the cosolvent may solubilize the lipophilic solute molecule, the effect on transport may be subtle and not easy to predict. At least three mechanisms may cause Pe and membrane retention (%R) values to alter as a result of the cosolvent addition. To a varying extent, all three mechanisms may simultaneously contribute to the observed transport ... 

The borole ring and various 1,3-diborolyl anions have been extensively employed as ligands to prepare a huge array of transition metal complexes and multidecker sandwich compounds.96 97 Inevitably, the electronic character of the borole is profoundly changed upon complexation, so a study of such complexes can reveal nothing certain about B—C multiple bonding in the isolated ligand. 

The [3]-l,2-dicarbaundecahydroundecaborate(2—) ion, B9-C2Hu2-, has been found to form sandwich compounds with iron5 and cobalt. d Two synthetic procedures, one in non-aqueous and the other in aqueous media, have been developed. The procedure in nonaqueous media is general, whereas that in aqueous media can be used only to prepare complexes which are not decomposed by base. Both methods of preparation are... 

The unsymmetrical complexes LnPcPc can also be prepared in a stepwise manner (Scheme 8.1, D, upper part) [87, 112-114]. Treatment of phthalonitrile with excess of Lu(OAc)3- H2Oand DBU gives the half-sandwich compound LuPc(0Ac)(H20)2. The latter complex reacts with Na2Nc in 1-chloronaphthalene leading to the formation of LuPcNc [87]. Similarly, the template reaction of unsubstituted and crown-substituted phthalonitriles with lutetium acetate was carried out in boding w-hexanol in the presence of DBU [115-117]. Bi- and tri-nuclear [118] lutetium complexes could also be obtained following this approach [111, 119]. 

Salts of [ ihalf-sandwich compounds 2-(ligand) -c/oxo-2,l-MCBioHii, but their potential as precursors is demonstrated in the synthesis of rhenium and platinum compounds. Thus salts of the dianion [2,2,2-(CO)3-c/oxo-2,l-ReCBioHnf have been prepared by... 

Methyl benzoate, anisole, and diphenyl ether each give sandwich compounds with chromium vapor, although in rather low yield (32, 55, 110). Chromium appears to attack alkyl ethers and this deoxygenation probably competes with complexation with the aromatic oxygen compounds. No simple product has been isolated from chromium atoms and aniline, but bis(7V,7V-dimethylaniline)chromium has been prepared (32). The behavior of molybdenum and tungsten vapors closely resembles that of chromium in reactions with oxygen- and nitrogen-substituted arenes (113). 

Another type of five-membered aromatic compound is the metallocenes (also called sandwich compounds), in which two cyclopentadienide rings form a sandwich around a metallic ion. The best known of these is ferrocene, although others have been prepared... 

Imidazolium ligands, in Rh complexes, 7, 126 Imidazolium salts iridium binding, 7, 349 in silver(I) carbene synthesis, 2, 206 Imidazol-2-ylidene carbenes, with tungsten carbonyls, 5, 678 (Imidazol-2-ylidene)gold(I) complexes, preparation, 2, 289 Imidazopyridine, in trinuclear Ru and Os clusters, 6, 727 Imidazo[l,2-a]-pyridines, iodo-substituted, in Grignard reagent preparation, 9, 37—38 Imido alkyl complexes, with tantalum, 5, 118—120 Imido-amido half-sandwich compounds, with tantalum, 5,183 /13-Imido clusters, with trinuclear Ru clusters, 6, 733 Imido complexes with bis-Gp Ti, 4, 579 with monoalkyl Ti(IV), 4, 336 with mono-Gp Ti(IV), 4, 419 with Ru half-sandwiches, 6, 519—520 with tantalum, 5, 110 with titanium(IV) dialkyls, 4, 352 with titanocenes, 4, 566 with tungsten... 

The range and versatility of amide anion binding hosts is very extensive. Macrocyclic amides have also been reported, such as 4.42 which forms a remarkable sandwich compound with sulfate in the solid state. Sulfate binding is enhanced by protonation of the tertiary amine groups and the host is thus a hybrid between amide and ammonium binding sites. The triethylbenzene scaffold has been used to prepare... 

For MALDI-TOF MS several sample preparations are available with different matrices (26). The choice of the matrix and of the sample preparation should be adapted to the molecular mass of the compounds and to the complexity of the samples to analyze. a-Cyano-4-hydroxycinnamic acid (4HCCA) is preferred for peptides between 1 and 15 kDa, and the sandwich sample preparation can be universally used for molecular mass determination of pure peptides and enzymatic fragments or complex mixtures (e.g., crude hemolymph, enzymatic digests). The procedures reported below are the ones used for the discovery of the Drosophila immune-induced peptides (19,27,30). 

While the mercury compound shows localized N—Hg bonds, the TADB-system (which is isoelectronic with cyclopentadiene) forms a low-spin complex with iron. This was the first identified example of a sandwich-compounds of a boron-nitrogen ring. The complex is prepared by adding an etheric solution of TADBLi to a suspension of FeCl2 in tetra-hydrofuran. 

On the other hand, there are indications that our expectations must not be set too high. A great variety of chemically extraordinary interesting transition metal organometallics has been prepared during the past decades. I think in particular of the types known as "sandwich compounds", exemplified by ferrocene, bisbenzenechromium, bis 7-allyl nickel and cyclobutadienemetal complexes ... 

A. R. Kudinov, and M. I. Rybinskaya, New Triple-Decker Complexes Prepared by the Stacking Reactions of Cationic Metallofragments with Sandwich Compounds, Russ. Chem. Bull. 48, 1615-1621 (1999). 

Some (porph)M(/z-0)3M(porph) complexes in which the metal atom lies well out of the porphyrin plane and is bonded to three oxygen atoms are known.32 Cationic sandwich compounds of the type [Ta(porph)2][TaCl6] can be prepared from TaCl5 and Li2(porph) while neutral half-sandwich compounds such as Ta(porph)Me3 can be made from TaMe3Cl2 and Li2(porph).33... 

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