Carbon-halogen, Group 8/9 metals

Meta.1 Oxides. Halogen-containing elastomers such as polychloropreae and chlorosulfonated polyethylene are cross-linked by their reaction with metal oxides, typically ziac oxide. The metal oxide reacts with halogen groups ia the polymer to produce an active iatermediate which then reacts further to produce carbon—carbon cross-links. Ziac chloride is Hberated as a by-product and it serves as an autocatalyst for this reaction. Magnesium oxide is typically used with ZnCl to control the cure rate and minimize premature cross-linking (scorch). 

Solutions of the halides of the beryllium group of elements can also be made by acting on the hydroxides or carbonates of the metals with the halogen acid. To take barium chlo-... 

In a general sense, the Reformatsky reaction can be taken as subsuming all enolate formations by oxidative addition of a metal or a low-valent metal salt into a carbon-halogen bond activated by a vicinal carbonyl group, followed by reaction of the enolates thus formed with an appropriate electrophile (Scheme 14.1).1-3 The insertion of metallic zinc into a-haloesters is the historically first and still most widely used form of this process,4 to which this chapter is confined. It is the mode of enolate formation that distinguishes the Reformatsky reaction from other fields of metal enolate chemistry. 

The effect of fluorinated systems on the reaction process shown in Figure 10.67 is of interest [139] it is to be noted that insertion of the palladium catalyst into the carbon-halogen bond may be considered as a nucleophihc attack by the palladium centre, albeit a soft nucleophile, which prefers to attack C—Br over C—F [138]. This process is, of course, aided by the presence of electron-withdrawing groups (EWG) in the organic system. It is likely, however, that co-ordination of the other reactant, e.g. alkyne, to the palladium is the rate-determining step [137], but this will be aided by EWGs attached to the metal. 

Oxidative addition of the carbon-halogen bond is a well-documented reaction for Group 10 transition metal complexes, but it is relatively limited for ruthenium. The example given here involves the reversible oxidative addition of allyl halide to RuCp(CO)2X to produce RuCp(p -allyl)X2 [78]. Oxidative addition of allyl halide to a Ru(0) complex Ru(l,5-COD)(l,3,5-COT) is also reported, but the product yield was poor [79]. Nevertheless, a catalytic Heck-type alkenylation of bromostyrene with methyl acrylate by Ru(l,5-COD)(l,3,5-COT) proceeded smoothly [80]. A cross-coupling reaction of alkenyl halide with Grignard reagents or alkyl lithium also pro-... 

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