Halides replacement

Hydride transfer from organic substrates to olefins (219) or halides (220), catalyzed by halogeno(triphenylphosphine)nickel complexes, and halide replacement reactions (example 13, Table VIII) by hydrolytic cleavage of nickel complexes have also been described. 

Organoborane intermediates can also be used to synthesize alkyl halides. Replacement of boron by iodine is rapid in the presence of base.150 The best yields are obtained with sodium methoxide in methanol.151 If less basic conditions are desirable, the use of iodine monochloride and sodium acetate gives good yields.152 As is the case in hydroboration-oxidation, the regioselectivity of hydroboration-halogenation is opposite to that observed for direct ionic addition of hydrogen halides to alkenes. Terminal alkenes give primary halides. 

Doubly bridged cationic diplatinum(II) complexes [Pt(o-CH2C6H4CN-fip )(2=P os)](BF4)2 have been synthesized by halide replacement. The cyano group remains bonded to platinum both in the solid state and in solution.492... 

Halide replacement occurs with other solvents. For the complexes PtCl2(L—L), the equilibrium position in equation (552) is driven to the right by strongly coordinating solvents S. The observed sequence is PR3 = py > Me2SO > DMF MeCN CO.2005... 

There is an alternate mechanism for halide replacement, following the sequence of nucleophile addition, protonation and elimination of HX (Scheme 9). In this pathway, the addition of the nucleophile need not be at the ipso position it can be ortho to halide leading to cine substitution or it can be at the meta or para positions, leading to tele substitution.69,70 The mechanism is the same for both cine and tele substitution and the different names reflect a differentiation in the IUPAC naming schemes. 

Tributyltin hydride (Bu3SnH) is used synthetically to reduce alkyl halides, replacing a halogen atom with hydrogen. Free-radical initiators promote this reaction, and free-radical inhibitors are known to slow it or stop it. Your job is to develop a mechanism, using the following reaction as the example. 

Both the Sandmeyer and Meerwein reactions have been interpreted by heterolytic and homolytic mechanisms. Both reactions resemble halide replacements by involving solutions of complexes of Cu(I) with the reacting species, a diazonium compound. Cohen and Lewin have reported that a mixture of p-tolyldiazonium tetrafluoroborate and copper benzoate in aprotic solvents rapidly evolves nitrogen and forms toluene, bi(/)-tolyl), />-tolyl benzoate, and p,p-dimethylazobenzene (54). As was earlier suggested by Kochi 177), the azobenzene derivative is believed to arise from a reaction between an arylcopper species and the diazonium compound. A similar mechanism was suggested for the analogous reac-... 

Reactions of ( -allyl)Fe(CO)3X complexes (135) have been restricted to silver salt-indnced halide replacement, CO... 

The amino group of 4-amino-3-pyrazolin-5-ones can be diazotized easily and the resulting diazonium salt couples with the usual reagents. Other diazonium salts couple with 4-amino-3-pyrazolin-5-ones at the amino group. Mercuric halides replace the amino hydrogen in 2,3-dimethyl-l-phenyl-4-sulfamino-3-pyrazolin-5-one.543 The 4-amino groups react normally with isothiocyanates,49 epoxides,1261 ureas1367 and nitrosamines.527... 

Ethylene derivatives from halides Replacement of chlorine by acetoxy groups Identification of isomeric, chlorinated fatty acid esters... 

The process involves initial formation of Ph M by halide replacement, followed by hydrogen transfer to allow arene -coordination . The reaction conditions complement those of the metal halide-aluminum halide-aluminum metal method and may be useful with specifically substituted arenes. 

Substitution of alkenyl and alkynyl halides. Replacement of the chlorides and fluorides with a methyl group in excellent yields is achieved with the cobaltate or ferrate reagent. 

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