Cuprous halides

Gattermann (1890) found that the preparation of the cuprous halide may be avoided by making use of the fact that finely-divided copper (e.g., freshly-precipitated or reduced by hydrogen or copper bronze) acts catal3d.ically in the decomposition of solutions of diazonium salts, for example ... 

The perfluorovmylcadmium compounds react with electrophiles as expected [144] (equation 111) and readily undergo metathesis with cuprous halides [145] (equation 112)... 

Sandmeyer reaction (Section 24.8) The nucleophilic substitution reaction of an arenediazonium salt with a cuprous halide to yield an aryl halide. 

Lithium dialkylcopper reagents can be prepared by mixing 2 mol of RLi with 1 mol of a cuprous halide in ether at low temperamres ... 

Pentafluorophenylcopper exists as a tetramer. It forms complexes with a variety of reagents and solvents as well as ate complexes a representative list is given in Table I. For many syntheses the crude reaction mixtures of cuprous halide with either pentafluorophenylmagnesium bromide, or pentafluorophenyllithi-um, or the pentafluorophenylcopper-dioxane complex react as well as the solvent-free tetramer. 

As with other metals, cupric and cuprous halides can detonate in contact with potassium. In addition, the action of cuprous chloride on lithium azide gives rise to a very violent reaction. 

Examples of the three mechanistic types are, respectively (a) hydrolysis of diazonium salts to phenols89 (b) reaction with azide ion to form aryl azides90 and (c) reaction with cuprous halides to form aryl chlorides or bromides.91 In the paragraphs that follow, these and other synthetically useful reactions of diazonium intermediates are considered. The reactions are organized on the basis of the group that is introduced, rather than on the mechanism involved. It will be seen that the reactions that are discussed fall into one of the three general mechanistic types. 

Aryl Halides from Diazonium Ion Intermediates. Replacement of diazonium groups by halides is a valuable alternative to direct halogenation for the preparation of aryl halides. Aryl bromides and chlorides are usually prepared by a reaction using the appropriate Cu(I) salt, which is known as the Sandmeyer reaction. Under the classic conditions, the diazonium salt is added to a hot acidic solution of the cuprous halide.99 The Sandmeyer reaction occurs by an oxidative addition reaction of the diazonium ion with Cu(I) and halide transfer from a Cu(III) intermediate. 

The muonium centers observed in the curpous halides (see Table II) are unusual in several respects compared with Mu in other semiconductors and insulators. Figure 12 shows the reduced hyperfine parameters for Mu in semiconductors and ionic insulators plotted as a function of the ionicity (Philips, 1970). The positive correlation is especially apparent for compounds composed of elements on the same row of the periodic table where the lattice constants and valence orbitals are similar (see solid points in Fig. 12). Note however that the Mu hyperfine parameters in cuprous halides lie well below the line and in fact are smaller than in any other semiconductor or insulator (Kiefl et al., 1986b). The reason for this unusual behaviour is still uncertain but may be related to other unusual properties of the cuprous halides. For example the upper valence band is believed... 

Replacement of the diazonium group by iodine does not require the presence of cuprous halide and is done simply by shaking the diazonium salt with potassium iodide. 

The insoluble complexes (27) have been prepared by the room-temperature reaction of the appropriate cyclo-octa-1.5-diene cuprous halide dimer with [(Tt-CpljTilSR),], in toluene, under an atmosphere of nitrogen. The existence of a Ti—Cu bond is suggested from comparative spectral studies with [(7t-Cp)2-... 

The stabilities of the triammino-cuprous halides are almost identical, and the dissociation pressures of the ammino-cupric halides lie very near together.6 The stabilities of hexammino-copper halides is also almost identical the compounds are very readily decomposed by water, and hence do not seem to be formed in aqueous solution. Ammino-derivatives of cupric carbonate, cupric acetate, cupric oxide, and cuprous cyanide and thiocyanate are known. These have the general characteristics of the ammines already described. 

Secondary and tertiary propargyl alcohols are directly converted to halo-allenes on reaction with concentrated aqueous hydrogen halides in the presence of the corresponding cuprous halide [60,72-73]. (See Table VII.) Better yields are obtained with hydrogen bromide. Hydrogen chloride yields chloroallene, propargyl chloride, and the chloro- 1,3-diene isomers (Eq. 60). 

The coupling reaction with active halides such as allyl halides or acid chlorides catalyzed by cuprous halides afforded the corresponding alkenylated compounds [131,167,168] (Scheme 57). 

A practical method for preparation of fluorinated alkenyl copper reagents has been recently developed from cuprous halides metathesis of the corresponding zinc or cadmium reagents [180]. These copper reagents exhibit excellent stability at room temperature and undergo a variety of coupling reactions with methyl, allyl, vinyl, aryl and acid halides [180] (Scheme 63). More recently, preparation of cyclic perfluoroalkenyl copper reagents has been reported by the same route [156-158]. 

Reaction CXXXIll. Action of Aromatic Halogen Compounds on Ammonia or Amino Compounds.—Aliphatic halides readily react with ammonia and amines according to Reaction CXXXII. Aromatic halides are less reactive, unless negative groups are also present. The addition of copper powder or cuprous halide greatly accelerates the elimination of halogen hydride. 

The Sandmeyer reaction requires the aromatic diazonium salt and cuprous halide (CuX). ... 

The unsaturated character of these trialkyl esters was shown by the ease with which they were attacked by nitric acid, but still more clearly by the formation, with evolution of heat, of stable crystalline addition compounds when they were mixed with cuprous halides. Thus CuC1.P(OC2H5)3 was described as consisting of colourless crystals melting at 190° to 192° C. and soluble in organic solvents.4 This property they share with phosphine, alkylphosphines and phosphorus trihalides. The phosphoric esters were quite indifferent to cuprous halides. Nor were such addition compounds formed either by phosphorous acid itself or by the dialkyl esters, which may show that the latter compounds have the unsymmetrical formula. Phosphorous acid probably exists in both forms, but first as P(OH)3, i.e. when produced from PC13 and Ha0.5 This may be transformed into the unsym-metrieal form through an addition compound HC1.P(0H)3,4 and probably also exists in the form of complex molecules, such as... 

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