Metal functionally substituted

Functionally substituted phosphines play an important role as ligands in a great variety of phosphorus coordination compounds. They have some interesting features that distinguish them from other phosphine ligands, namely (a) the presence of other heteroatoms bearing lone electron pairs in addition to phosphorus (b) the presence of functional groups able to form bonds with a metal with the participation of its valence electrons ... 

The straightforward generation of lithiated allenes [31], in particular lithiated donor-substituted allenes [32], has opened up smooth and efficient routes to further metallated functionalized allenes. By transmetallation, metals such as magnesium,... 

A common feature of any cyclization reaction is that a new intramolecular C—C bond is produced that would not have been formed in the absence of the catalyst. Those reactions in which one ring closure step is sufficient to explain the formation of a given cyclic product will be called simple cyclization processes, although their mechanism is, as a rule, complex. We shall distinguish those cases in which any additional skeletal rearrangement step(s) is (are) required to explain the process. Some specific varieties of hydrocarbon ring closure processes are not included. A recent excellent review deals with the formation of a second ring in an alkyl-substituted aromatic compound (12). Dehydrocyclodimerization reactions have also to be omitted—all the more since it is doubtful whether a metallic function itself is able to catalyze this process (13). 

Ethylbenzene Isomerization Isomerization of EB requires both metal and acid function. Hydrogenation results in an intermediate naphthene. The acid function is required to isomerize the naphthene to a methyl-ethyl-substituted five-mem-bered ring species that can further convert to a dimethyl-substituted six-membered ring naphthene. This can be dehydrogenated by the metal function to a xylene isomer, OX in the example shown in Figure 14.9. 

The use of lithionaphthalene and lithio 8-methylnaphthalene as functionally substituted anionic initiators is very disappointing (21, 22). The deactivation of living polyanions onto a-bromonaphthalene or bromo-8-methylnaphthalene is another unsatisfactory approach due to metal halogen interconversion (eqs 9, 10) (23). 

Why did he think this was so One answer is that alkanes are available as raw material for the chemical industry, and new reactions by which they can be converted into functionally substituted organic compounds are likely to be of considerable interest to the industrial chemist. A second answer is that the nature of any interaction between an alkane and a transition metal must be quite different from that of other hydrocarbons (i.e., alkenes, alkynes, and aromatic compounds) having 7r-electrons that can play a dominant role. 

Fluxional and Nonrigid Behavior of Transition Metal Organometallic ir-Complexes, 16, 211 Free Radicals in Organometallic Chemistry, 14, 345 Functionally Substituted Cyclopentadienyl Metal Compounds, 21,1... 

This process, shown as mode 2 in Fig. 2, involves the production and reaction of functionally substituted silyl and silanediyl species. Since this occurs while the silicon-metal bond remains intact, it is not surprising that most of the entries in Table XII relate to compounds with robust Si-Mn and Si-Fe bonds other examples involve bonds to Cr, Mo, W, Re, Pt, and even Co. The types of exchange reaction observed will be dealt with in turn. 

The effective atomic number (EAN) rule is useful for interpreting how ligands with more than one double bond are attached to the metal. Essentially, each double bond that is coordinated to the metal functions as an electron pair donor. Among the most interesting olefin complexes are those that also contain CO as ligands. Metal olefin complexes are frequently prepared from metal carbonyls that undergo substitution reactions. 

Displacing the Essential Metal Ion in Biomolecules. It is estimated that approximately one third of all enzymes require metal as a cofactor or as a structural component. Those that involve metals as a structural component do so either for catalytic capability, for redox potential, or to confer steric arrangements necessary to protein function. Metals can cause toxicity via substitution reactions in which the native, essential metal is displaced/replaced by another metal. In some cases, the enzyme can still function after such a displacement reaction. More often, however, enzyme function is diminished or completely abolished. For example, Cd can substitute for Zn in the protein famesyl protein transferase, an important enzyme in adding famesyl groups to proteins such as Ras. In this case, Cd diminishes the activity of the protein by 50%. Pb can substitute for Zn in 8-aminolevulinic acid dehydratase (ALAD), and it causes inhibition in vivo and in vitro. ALAD contains eight subunits, each of which requires Zn. Another classic example of metal ions substituting for other metal ions is Pb substitution for Ca in bones. 

Metal-Assisted Substitution of Hydrogens a to a Carbonyl Functionality... 

One of the most convenient synthetic routes for the preparation of vinyl fluorides 2 is by treatment of the corresponding vinyltin compounds 1 with electrophilic fluorinating reagents. This procedure is also used for the preparation of aryl fluorides, since it is well-established that fluorination with electrophilic reagents is facilitated by ipso substitution of a suitable, usually weakly bonded, metal function. In the case of aryl fluorides, the reaction is also carried out using elemental fluorine as the fluorinating agent. ... 

Functionally Substituted Cyclopentadienyl Metal Compounds, 21,1 Heterocyclic Organoboranes, 2, 2S7... 

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