Halide abstraction reactions

The AgCl precipitate is removed by filtration and any excess silver ions are electrochemically removed. Other workers have utilized the [Pt(H20 4]2+ ion in a number of substitution reactions. 

Seigmann, Pregosin, and Venanzi O have carried out related reactions in which removal of coordinated chloride ions leads to the formation of complexes containing solvento-ligands (solv = H2O or MeOH), Eq. 3.2  

Similarly, [NbCl2lCp2] reacts with two equivalents of silver perchlorate in acetone22 to form [NbCl(Me2C0)2Cp2][C104]2. The compound has been isolated in the solid state and characterized by elemental analysis, as well as IR and NMR spectroscopies. Both 2,2 -bipyridyl and 1,10-phenanthroline readily displace the coordinated acetone molecules. 

When halide abstraction reactions are performed with silver salts in water or in non-aqueous solutions, halide ions are abstracted according to the solubility product of the silver halide (Table 3.1) with the least soluble salts being the first to be precipitated. Abstraction follows the sequence I Br Cl F . Accordingly, then, the interaction of [NbCl2lCp2l with one mole equivalent of silver perchlorate in acetone leads to the formation of [NbCl2(Me2C0)Cp2][C104] and precipitation of Agl.22 

Solubility products23 of silver halides in some non-aqueous solvents 

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The converse of polymerization is heterolytic bond scission leading either to R3Sn+ or R3Sn species. Tricoordinate organotin(IV) cations can readily be synthesized at room temperature by hydride or halide abstraction reactions in benzene or other solvents.For example, with R = Me, Bu or Ph ... 

Halide abstraction reactions with these carborane derivatives gives sometimes intermediate products rather than metathesis, as in the reaction of Ag(6,7,8,9,10-Br5CB9H5)(r/2-C7I Ix) with [IrCl(CO)(PPh3)] that yields an Ir—Ag adduct (238),1350 or the reaction of [MoCpI(CO)3] with Ag(CBnH12) which gives (239).I357 135 ... 

Fluoride complexes of organometallics can be readily prepared by halide abstraction reactions. The general reaction scheme for a carbonyl species ... 

Mono(cyclopentadienyl) halides, with Ti(IV) alkyl- and alkenyl-substituted Cp ligands, 4, 383 boryl-Cp ligands, 4, 392 halide abstraction reactions, 4, 405 hydrolysis reactions, 4, 398 metathesis reactions, 4, 400... 

Halide abstraction reactions are very common and usually fast processes. These reactions have also proved extremely useful for two specific applications in the field of physical organic chemistry. First, for obtaining thermochemical stability data of carboca-tions through the measurement of gas-phase chloride transfer equilibria (equation 1). 

Hydrolysis, redox, metathetical, and halide abstraction reactions are covered here. Some of these reactions lead to specific complexes with Ti-O, Ti-N, and Ti-C bonds which are described in subsequent sections. Comments on the applications of the mono-Cp trihalo titanium complexes as olefin polymerization pre-catalysts have been mentioned in Section 4.05.3.1.1 and some recent advances in this field are also considered here. (See Chapter 4.09 of this work.)... 

Addition reactions of the 4-tm-butylcyclohexyl radical have been studied with a variety of alkenes and also in atom-abstraction reactions (see Section D.2.2.)3 58. While hydrogen or halide abstraction reactions yield preferentially the axial product, unselective addition occurs with terminally unsubstituted alkenes. In addition reactions of alkenes substituted by alkyl groups at the attacked olefinic center, the preference for axial attack decreases further and the equatorial addition product is formed. This influence of the size of the reaction partner on the selectivity is rationalized on the basis of the simultaneous presence of steric effects (hindering axial attack) and torsional effects (hindering equatorial attack), very similar to those discussed for nucleophilic addition reactions to cyclic ketones59. 

Tl, ) salts have proven to be useful for halide abstraction reactions that generate coordinatively unsaturated species. 

Efficient halide abstraction reactions using silver(I) and thallium(I) salts are among the most widely applied methods to generate cationic platinum(II) or palladium(II) species that are often active catalysts. There is increasing evidence for the involvement of metal-metal-bound, heterobimetallic intermediates in these salt metathesis reactions. Two isolable examples of such intermediates have been reported recently (Scheme 24). 

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