General Methods of Preparation

Alkyne complexes of virtually every transition metal are known. The range of structural types is striking—included are compounds with one, two, or three acetylenes, a similar ran in the number of metal atoms, and a variety of ancillary ligands such as carbon monoxide, phosphines, halides, cyclopentadienyk and others. 

Preparative information for selected complexes is presented in Table 1. The listing is not exhaustive but is limited instead to those classes of compounds for which a few different alkynes have been complexed or to those in which the chemistry of the coordinated alkyne has been studied to some extent. 

Almost all acetylene complexes have been prepared by one of two methods ligand substitution [Eq. (1)] or reductive complexation [Eq. (2)]. 

Ligand substitution is by far the most common method, proceeding thermally in some cases and photochemically in others, with carbon monoxide being the ligand most often replaced. The reductive method has been limited largely to the preparation of Group VIII complexes. The yields from either route vary widely and few attempts have been made to improve or optimize them. This certainly is one area in which further development is required in order to enhance the attractiveness of these complexes as synthetic intermediates. 

N0(C0)L20s(Me2C0) + N0 C0)L20s(RCjR) — Segal and Johnson, 1975 

General Methods of Preparation. - A review has been published 

Similarly, the silyl enol ethers of B-keto-esters may be oxidized 

HMPA-triethylamine to cyclopentanols has been described. Opening of dihydropyrans with a base comprising LDA and potassium t-but- 

4-dienols in moderate yields. A full paper has been published detailing work on the vanadium-molybdenum complex-catalysed isomerization of allylic alcohols with bis(trimethylsilyl) peroxide, which produces the alcohol possessing the highest degree of 94 

Reagents. i.Me SiCt, Znl2, CH2CI2, reflux ii, HCl.MeOH iii, aq.NaOH 

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An important general method of preparing indoles, known as the Fischer Indole synthesis, consists in heating the phenylhydrazone of an aldehyde, ketone or keto-acld in the presence of a catalyst such as zinc chloride, hydrochloric acid or glacial acetic acid. Thus acrtophenone phenylhydrazone (I) gives 2-phenyllndole (I V). The synthesis involves an intramolecular condensation with the elimination of ammonia. The following is a plausible mechanism of the reaction ... 

Generalized methods of preparation include the reaction of /3-keto esters (or amides) with hydroxylamine, a-alkynic and a,/3-unsaturated esters (or amides) with hydroxylamine (real or generated in situ), hydroxylamine and nitrile oxides, and /3-keto and a-alkynic nitriles with hydroxylamine (62HC(l7)l, pp. 3,7). 

This reaction is a general method of preparation for aryl isothiocyanates in yields of 50-75 per cent of the theoretical amount. 

The general method of preparation for the original polyimides is shown in Figure 18.35. 

The general method of preparation of the polysulphides is to add the dihalide slowly to an aqueous solution of sodium polysulphide. Magnesium hydroxide is often employed to faeilitate the reaction, which takes 2-6 hours at 70°C. 

After a brief historical review in Chapter 1 the following five chapters provide a short summary of the general methods of preparation of plastics materials and follow on by showing how properties are related to chemical structure. These particular chapters are largely qualitative in nature and are aimed not so much at the theoretical physical chemist but rather at the polymer technologist and the organic chemist who will require this knowledge in the practice of polymer and compound formulation. 

Carbon forms binary compounds with most elements those with metals are considered in this section whilst those with H, the halogens, O, and the chalcogens are discussed in subsequent sections. Alkali metal fullerides and encapsulated (endohedral) metallafullerenes have already been considered (pp. 285, 288 respectively) and met-allacarbohedrenes (metcars) will be dealt with later in this section (p. 300). Silicon carbide is discussed on p. 334. General methods of preparation of metal carbides are ... 

This method is illustrative of a general method of preparing simple ketones from normal aliphatic carboxylic acids. It is especially useful because the starting materials are easily accessible, the yields good, and the procedure very simple. 

The present procedure was adapted from a general method of preparing aromatic alcohols recently described.5... 

A. General Methods of Preparation of Sulphones from Sulphoxides. . . 970... 

The synthesis of 2-chloro-2,3,3-trifluorocyclobutyl acetate illustrates a general method of preparing cyclobutanes by heating chlorotrifluoroethylene, tetrafluoroethylene, and other highly fluorinated ethylenes with alkenes. The reaction has recently been reviewed.11 Chlorotrifluoroethylene has been shown to form cyclobutanes in this way with acrylonitrile,6 vinylidene chloride,3 phenylacetylene,7 and methyl propiolate.3 A far greater number of cyclobutanes have been prepared from tetrafluoroethylene and alkenes 4,11 when tetrafluoroethylene is used, care must be exercised because of the danger of explosion. The fluorinated cyclobutanes can be converted to a variety of cyclobutanes, cyclobutenes, and butadienes. 

This is a general method of preparing trialkylnitromethanes from the corresponding (trialkylmethyl)amines.2-4 Table I lists... 

The crystal chemistry of the borides is discussed in 6.7.2 according to this scheme. General methods of preparation, single-crystal growth and sintering of borides is considered, respectively, in 6.7.3, 6.7.4 and 6.7.5. 

We have recently developed a general method of preparation of the heretofore relatively unknown trialkyltriazenes ( ). These substances are readily prepared by reaction of a Grignard reagent or an alkyllithium with an alkyl azide, followed by the reaction of the Intermediate dlalkyltrlazene with base, and alkylation of the resulting trlazenyl anion with an alkyl halide. 

The most general method of preparing pentafluorophenylgold(III) derivatives is oxidative addition with the appropriate oxidant to the gold(I) complex. The choice of... 

In favor of a dihydrogen intermediate, the following should be noted (i) the addition of HX molecules to OsHCl(CO)(P Pr3)2 is a useful synthetic route for dihydrogen compounds (vide infra), (ii) the electrophilic character of the dihydrogen complexes has been demonstrated,38 and (iii) the addition of electrophiles to metal alkynyl complexes is a general method of preparing vinylidene compounds.39... 

The patented preparation of peroxyacids [2] by interaction of carboxylic acids with hydrogen peroxide in presence of metaboric acid needs appropriate safeguards to prevent accidental separation of the cone, peroxyacids [3], Much descriptive data on stabilities of a wide selection of peroxyacids has been summarised [4], A general method of preparation of peroxyacids involving addition of e.g. the anhydrides of acetic, maleic, phthalic or trifluoroacetic acids to a suspension of 90%... 

Reduction of all three of the double bonds in the pyrrolo-benzodiazepine-5,11-dione 105 with excess potassium provides the corresponding trans fused hexahydrobenzene derivative 106 in high yield with complete stereochemical control. The preparation of (+)-perhydro-219A 108 from 106 has been reported 3 and a general method of preparation of derivatives of /ra i-2-aminocyclohexanecarboxylic acid e.g. 107) has recently appeared. 

I he procedure described is patterned after the method suggested by Vogel, Schubart, and Boll, and it illustrates a general method of preparing oxepins. Furthermore, the first step represents an example of the Birch reduction of an aromatic hydroearl )on. The second step is illustrative of the selective epoxidation of a diene system. ... 

These polymers possessing amide linkages are Important examples of synthetle fibres and are termed as nylons. The general method of preparation eonslsts of the condensation polymerisation of diamines with dlearboxylle aelds and also of amino acids and their laetarns. 

A new general method of preparation of raetal-PF3 complexes using [Ni-(PF3) ] as the reactant has been reported. The reactions performed and their products are given in Table 4. The structure of [ [(cyclohexyl)2P]2CH2 2Ni] shows the metal to have distorted tetrahedral co-ordination and the acute P—Ni—P angle of 77° is suggested as indicating bent Ni—P bonds. 

Another general method of preparation involves the reaction of cyclopentadiene with sodium metal or sodium hydride in tetrahydrofuran (THF). Addition of iron(ll) chloride to this solution forms the complex dicyclopenta-dienyliron ... 

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