Preparation of complexes

Low temperature fluorination techniques (—78° C) are promising for the preparation of complex fluorinated molecules, especiaUy where functional groups are present (30), eg, fluorination of hexamethjiethane to perfluorohexamethylethane [39902-62-0] of norbomane to perfluoro- (CyF 2) 1-hydro undecafluoronorbomane [4934-61 -6] C HF, and of adamantane to 1-hydropentadecafluoroadamantane [54767-15-6]. 

V. Pichon, M. Bouzige, C. Miege and M. C. Hennion, Immunosorbents natural molecular recognition materials for sample preparation of complex environmental matrices . Trends. Anal. Chem. 18 219-235 (1999). 

The hydrofluoride method can be used successfully both for the preparation of complex fluoride compounds and of complex oxides. The main advantage is that the synthesis is performed at relatively lower temperatures. In addition, the complex oxide material is formed through its respective fluoride compound and the product obtained is therefore more consistent. For instance, Co4Nb209 can be prepared using the hydrofluoride method at 900-1100°C, whereas the regular synthesis, based on the interaction of simple oxides, requires extended treatment at about 1400°C. 

These alkene isomers are separately available (4) by treatment of threo-S-trimethylsilyloctan-4-ol, prepared by reduction of the corresponding ketone with DIBAL in pentane at —120°C, with base or acid. The preparation of 5-trimethylsilyloctan-4-one itself illustrates three general procedures the addition of alkyl lithium reagents to vinylsilanes to generate a-lithiosilanes, the preparation of complex /5-hydroxysilanes, as diastereoisomeric mixtures, and the oxidation of such compounds to /8-ketosilanes... 

The Claisen condensation of t-butyl acetate with a methyl ester is a general route for the preparation of complex P-ketoesters.4 The reaction requires an excess of the enolate of t-butyl acetate to rapidly deprotonate the product and prevent tertiary alcohol formation. Some workers have also used excess LDA or t-butoxide for this purpose. 

Ring closure reactions are in many cases useful synthetic procedures in organic chemistry. They allow the preparation of complex molecules with high stereoselectivity and good yields. 

Malacria, M. (1996) Selective Preparation of Complex Polycyclic Molecules from Acyclic Precursors via Radical Mediated or Transition Metal-Catalyzed Cascade Reactions. Chemical Reviews, 96, 289-306. 

This chapter focuses on the description of boron-containing preceramic polymers, which are currently used for the preparation of complex shapes and have been... 

The heteroatom-assisted Diels-Alder reaction has emerged as an extremely powerful method for the preparation of complex heterocycles. In several cases, such reactions with TADs are described. For example, the reaction of vinyl pyrrolidone 594 with MTAD provides a 7 2 mixture of diastereomers 595 and 596 in 95% combined yield, showing only low face selectivity (Equation 88) <2005JOC5221>. 

It should be noted that the preparation of complexes (RNC)AuCN can be carried out via very special routes. Thus AuCN reacts with Mel to give (MeNC)AuCN. This reaction involves an interesting A-alkylation of an Au(i)-bound cyanide group.219 Other (RNG)AuGN complexes were obtained from the reaction of K[AuC14] with the isocyanide in methanol. Examples are the compounds (L)Au2(CN)2 with L = l,8-diisocyano-/>-menthane or 2,5-diisocyano-2,5-dimethyl-hexane. The reactions proceed with a dealkylation of an isocyanide in the coordination sphere of a gold(m) center to produce free cyanide (Scheme 53).201... 

Note that this reaction can also be used for the preparation of complexes with mixed substituents if the alkylating agent has a different group. Such complexes have also been generated by ring cleavage of trinuclear complexes, for example, with acyl halides (Equation (47)).2... 

The [2+2+1] cycloaddition of an alkene, an alkyne, and carbon monoxide is known as the Pauson-Khand reaction and is often the method of choice for the preparation of complex cyclopentenones [155]. Groth and coworkers have demonstrated that Pauson-Khand reactions can be carried out very efficiently under microwave heating conditions (Scheme 6.75 a) [156]. Taking advantage of sealed-vessel technology, 20 mol% of dicobalt octacarbonyl was found to be sufficient to drive all of the studied Pauson-Khand reactions to completion, without the need for additional carbon monoxide. The carefully optimized reaction conditions utilized 1.2 equivalents of... 

TMC ATRA reactions can also be conducted intramolecularly when alkyl halide and alkene functionalities are part of the same molecule. Intramolecular TMC ATRA or atom transfer radical cyclization (ATRC) is a very attractive synthetic tool because it enables the synthesis of functionalized ring systems that can be used as starting materials for the preparation of complex organic molecules [10,11], Furthermore, halide functionality in the resulting product can be very beneficial because it can be easily reduced, eliminated, displaced, converted to a Grignard reagent, or if desired serve as a further radical precursor. The use of copper-mediated ATRC in organic synthesis has been reviewed recently and some illustrative examples are shown in Scheme 3 [10,11,31,32,33],... 

Domino reactions present a modern approach in organic synthesis since they allow the preparation of complex molecules starting from simple substrate in a few steps and in many cases with high stereoselectivity. Moreover, as multi-component transformation they are highly suitable for combinatorial chemistry and give access to libraries of great diversity. 

Moreover, when MNA (8), MBA (9) or PMT (10) react with di-iodine trader the same experimental conditiorrs as in the case of the preparation of complex (7) (see above), neutral distrlfides were produced with formulae [(MNA)J (27), [(MBA) ] (28) and [(PMT)J (29) according to the reaction shown in Scheme 13.1. 

The use of glycosynthases as biocatalysts for the formation of glycosidic linkages has proven to be an effective and versatile tool for the preparation of complex oligosaccharides. The procedure is simple and reproducible and can be applied to a number of substrates involving carbohydrate and noncarbohydrate moieties. 

All attempts to bond R3P7 as a ligand to metal(O) complexes have failed. In contrast, the preparation of complexes with the related cage-molecules Pi (Sime2)3 was successful (8 ). 

The synthetic chemistry associated with the preparation of complexes containing diyne or diynyl ligands and their longer chain analogues is now well established. In many cases, metal cluster reagents react with systems containing multiple C=C... 

Fig. 28 Preparation of complex 45 containing the double ylide C(PMeR2) (SPh2) as ligand...

Some bidentate bis(imidazolin-2-ylidene)s 18 have been used for the preparation of complexes with chelating dicarbene ligands [75-80]. The synthesis, properties, and coordination chemistry of tripodal tris(imidazolin-2-ylidene) ligands like 19... 

The reaction of the free carbene with a suitable metal complex is the simplest method for the preparation of an NHC complex (Fig. 8a). In addition, the cleavage of electron-rich enetetramines in the presence of coordinatively unsaturated metal complexes followed by coordination and stabilization of the NHC also constitutes an established method for the preparation of NHC complexes (Fig. 8b) [7, 95], which works particularly well for the preparation of complexes with benzimidazolin-2-ylidene ligands [56, 80, 96]. 

This residue is a mixture of stereoisomerio dicyclohexyl-18-crown-6 polyethers which may be contaminated with some unchanged dibenzo-18-crown-6 polyether and with alcohols arising from hydrogenolysis of the polyether ring. The submitter reports that this residue is sufficiently pure for many purposes such as the preparation of complexes with potassium hydroxide which are soluble in aromatic hydrocarbons. 

Addition of halogens or interhalogens to perfluorohalogenothio-ketones, as already described, represents an important method for the preparation of complex sulfenyl halides. 

The epoxide functionality has tremendous versatihty in the preparation of complex molecules, since its treatment with a nucleophile affords an alcohol, two contiguous stereocenters, and a new carbon-carbon or carbon-heteroatom bond in a single step. 

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