Nickel-lead system, application method

Advancements in materitJs have been one of the most important factors in the development of corrosion-resistant automobiles. For automobile body and chassis parts, use of precoated sheet steel in critical areas, as demonstrated in Fig. 5, is one of the most effective methods of combating corrosion. Early on, hot dip gttlvanized steel and Zincro-metal coated steel were used to prevent perforation corrosion from the inside out in auto-body applications. Today a wide range of materi tls is used including hot dip and electrodeposited zinc, zinc-iron, zinc-nickel, and zinc-nickel/ organic composite coated steel. Other materials include aluminum and aluminum-zinc coated steels for exhaust systems and some structural components, teme (tin-lead) coated steel for fiiel tanks, and tin coated steel [23-25],... 

The last method, F, which uses NiCl2-2,2 -bipyridine complex, works well only for the most reactive aryl iodides [31]. It is mechanistically more complicated because here lead(II) bromide acts as the source of lead(O) which actually reduces Ni"(bpy)X2 back to the catalytically active Ni (bpy). Since the 2,2 -bipyridine 75 is somewhat more electron-rich ligand than simple 2,2 -bipyridine (5), the resulting nickel(II) complex employed in the related Chen s method is slightly more reactive with electron-poor aryl halides, e.g. bromides, but generally the method is applicable only with aryl iodides [30]. For instance, both iodo- and bromobenzene gave biphenyl (8) in 98 and 88% yields, respectively, but 2-bromothiophene was coupled in only 22% yield [30], Scheme 8. Chromium(II) chloride in a catalytic amount was used as an intermediate reductant as it provides an effective redox system, Cr(II) / Cr(III) between Ni(0) / Ni(II) and metallic manganese as the ultimate reductant. 

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