Halides late metal

The catalytic cycles for reduction of alkyl and atyl halides using Ni(o), Co(i) or Pd(o) species are interrupted by added carbon dioxide and reaction between the first formed carbon-metal bond and carbon dioxide yields an alkyl or aryl car-boxylate. These catalyses reactions have the advantage of occuriiig at lower cathode potentials than the direct processes summarised in Table 4.14. Mechanisms for the Ni(o) [240] and Pd(o) [241] catalysed processes have been established. Carbon dioxide inserts into the carbon-metal bond in an intermediate. Once the carboxy-late-metal species is formed, a further electron transfer step liberates the carboxy-late ion reforming the metallic complex catalyst. 

The cleavage of allcylamine N-H bonds by late transition metals to form metal amido complexes is also rare [69, 70]. When the transition metal is a low valent, late metal, the resulting amido complexes are highly reactive [71, 72]. It appears that the amination of aryl halides can involve an unusual N-H activation process by a palladium alkoxide to form a highly reactive palladium amide [65, 73]. 

In comparison with classic Lewis acids derived from main group halides (e.g., B, Al, Sn), f-elements, and early transition metal halides, late transition metal Lewis acids often are more inert to ubiquitous impurities such as water, offer higher stability, tunable properties by ligand modification, and a well-defined structure and coordination chemistry, thus allowing detailed studies of reaction mechanisms, and a rational basis for catalyst optimization. Among this new class of late transition metal Lewis acids, ruthenium complexes - the subject of this chapter - display remarkable properties... 

What is fhe implication of our work wifh respect to the metal-catalyzed polymerization of polar vinyl monomers FirsL for fhe late metal compounds, fhe polar vinyl monomers can clearly outcompete efhene and simple 1-alkenes wifh respect to insertion. However, fhe ground-state destabilization of the alkene complex that favors the migratory insertion of fhe polar vinyl monomers is a two-edged sword because it biases the alkene coordination towards ethene and l-alkenes. Indeed, we have observed fhe near quantitative displacement of vinyl bromide by propene to form 7 from 3 (Scheme 9.1). Thus, the extent of incorporation of fhe polar vinyl monomer in fhe polymer will depend on the opposing trends in alkene coordination and migratory insertion. The above discussion does not take into account the problem of functional group coordination for acrylates or halide abstraction for vinyl hahdes. 

When a late metal such as Pd or Rh catalyzes a substitution reaction of an organic halide, the first step is oxidative addition to the C—X bond. 

TT-Benzyl complexes typically form when a benzyl group is present in a coordina-tively unsaturated middle or late metal center that can participate in back-donation into the TT-benzyl urut. TT-Benzyl complexes have been prepared by the addition of benzyl Grignard reagents to unsaturated metal-halide complexes, by the addition of benzyl halides to low-valent metal complexes, or by the insertion of vinylarenes into metal hydrides or alkyls. These three types of reactions are illustrated by the examples in Equations 3.70-3.72. 

Many of the typical reactions that form transition metal-heteroatom bonds can be used to prepare late transition metal alkoxides. - For example, metathetical exchange between late metal halides and alkali metal salts of the corresponding alcohols often forms late metal alkoxides. Complexes that are more reactive than metal halides, such as metal acetates or triflates, are sometimes used when exchanges with halides are slow or reversible (Equation 4.66). Late metal fluorides can also be used for these exchanges, as shown in Equation 4.67. ... 

In chemistry related to the reactions of alkali metal alkoxides with late metal halide complexes, late metal alkoxides have been formed by the reaction of alcohols with metal halides in the presence of a base. This process has been used to form arylpalladium alkoxides during the coupling of aryl halides with alcohols discussed in Chapter 19 (cross-coupling). In addition, Milstein used an intramolecular version of this process to prepare the metallaoxetane in Equation 4.68. ... 

Thus, the initiating systems for the living polymerization consist of a halogenated initiator and a transition metal complex. The effective metal complexes for the catalysis now include various early and late transition metals as reviewed in this chapter, while the initiators are typically polyhaloalkanes, a-haloesters, (a-haloalkyl)benzenes, and sulfonyl halides. The metal-catalyzed polymerization can control the reactions of a... 

A variety of complexes of the thionyl imide anion [NSO] with both early and late transition-metal complexes have been prepared and structurally characterized. Since both ionic and covalent derivatives of this anion are readily prepared, e.g., K[NSO], McsMNSO (M = Si, Sn) or Hg(NSO)2, metathetical reactions of these reagents with transition-metal halide complexes represent the most general synthetic method for the preparation of these complexes (Eq. 7.10 and 7.11). ... 

These are of two main types compounds of M", which for platinum have been known since the beginning of this century and commonly involve the stable [PtMes] group and compounds of the divalent metals, which were first studied by J. Chatt and co-workers in the late 1950 s and are commonly of the type [MR2L2] (L = phosphine). In the Pt" compounds the metal is always octahedrally coordinated and this is frequently achieved in interesting ways. Thus the trimethyl halides, conveniently obtained... 

Several important classes of polar monomers have so far eluded copolymerization by the Pd(II) system. Vinyl chloride insertion, for example, leads to catalyst deactivation following P-halide elimination to form inert chloride species such as 1.32, as shown by Jordan [90], Similarly, attempted vinyl acetate copolymerization results in deactivation by an analogous acetate elimination process, although the ester chelate intermediate that forms after insertion also effectively shuts down the reaction [90], Therefore, -elimination of polar groups represents a significant and unresolved problem for late transition metal polymerization systems unless access of the metal to it is restricted. 

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