Metal insertion substitution reactions

Palladiumphthalocyanine (PcPd) can be synthesized from phthalimide, ammonium molyb-date(VI), urea and palladium(II) chloride in nitrobenzene.285 Peripherally substituted palladium phthalocyanine is prepared by the reaction of phthalonitrile286 or isoindolinediimine114,117 and palladium(II) acetate in 2-(dimethylamino)ethanol. Also a metal insertion into metal-free phthalocyanine in dimethylfonnamide starting from bis(triphenylphos-phane)palladium(II) chloride has been performed.141,287... 

These reactions involve metallate rearrangements , migratory insertion and transition metal-catalysed vinylic substitution reactions. They also perform well in applications in natural product synthesis . Many useful synthetic possibilities arise from application of ring-closing olefin metathesis (RCM) to unsaturated homoaldol products and their derivatives by means of the Grubbs catalyst 3942 4-286 Equation 105 presents some examples. ... 

Chromatography cyclophosphazenes, 21 46, 59 technetium, 11 48-49 Chromites, as spinel structures, 2 30 Chromium, see Tetranuclear d-block metal complexes, chromium acetylene complexes of, 4 104 alkoxides, 26 276-283 bimetallics, 26 328 dimeric cyclopentdienyl, 26 282-283 divalent complexes, 26 282 nitrosyls, 26 280-281 trivalent complexes, 26 276-280 adamantoxides, 26 320 di(/ >rt-butyl)methoxides, 26 321-325 electronic spectra, 26 277-279 isocyanate insertion, 26 280 substitution reactions, 26 278-279 [9]aneS, complexes, 35 11 atom... 

Zirconium and hafnium dialkylamides are highly reactive compounds. They undergo (i) protolytic substitution reactions with reagents such as alcohols, cyclopentadiene and bisftrimethylsilyOamine 63 64 (ii) insertion reactions with C02, CS2, COS, nitriles, phenyl isocyanate, methyl isothiocyanate, carbodiimides and dimethyl acetylenedicarboxylate 69-72 and (iii) addition reactions with metal carbonyls.73 These reactions are summarized with reference to Zr(NMe2)4 in Scheme 1. 

Olefinic compounds will often insert into carbon-transition metal bonds as CO does, and this reaction is an important step in many catalytic syntheses. When this step is combined with an oxidative addition of an organic halide to a palladium(O) complex in the presence of a base, a very useful, catalytic olefinic substitution reaction results (26-29). The oxidative addition produces an organopalladium(II) halide, which then adds 1,2 to the olefinic reactant (insertion reaction). The adduct is unstable if there are hydrogens beta to the palladium group and elimination of a hydridopalladium salt occurs, forming a substituted olefinic product. The hydridopalladium salt then reforms the... 

The usual products obtained from metal insertion reactions are shown in Table 3. They are used as starting materials for any axial ligand substitution processes. 

A special case of substitution reaction is the migratory insertion (see Migratory Insertion) reaction of alkyl or aryl metal carbonyls (see equation 58), by which an alkyl or aryl metal carbonyl is converted into an acyl or aroyl metal carbonyl by the action of a Lewis base. This reaction has been studied extensively, and in the case of Mn(Me)(CO)5 is found to proceed through a coordinatively unsaturated tetracarbonyl resulting from methyl migration on to one of the terminal CO groups in a cis position, (see equation 59). ... 

The reactivity of the cationic Zr complexes is a direct consequence of their Lewis acidity see Lewis Acids Bases) (i) various substitution reactions can occur into the Zr-solvent weak bond, (ii) unsatnrated substrates (CO, alkenes, alkynes, or ketones) insert into the Zr-C bond, potentially leading to polymerization reactions (see Section 8.2), (iii) new organic ligands obtained after reaction in the coordination sphere of the metal can be spontaneously released by /3-H elimination see -Hydride Elimination), or (iv) C-H bond activation of suitable ligands can occur. 

In a broad class of reactions of CH bonds with low-valent transition metals, however, the metal inserts into a CH bond of the alkane to give an alkylmetal hydride in which there is often a preference for formation of the least substituted alkyl. In any subsequent fimctionalization, the linear (or least branched) product is obtained, for example, nPrX and not iPrX. Since the branched product can be obtained... 

An aryl halide such as chlorobenzene is relatively unreactive towards nucleophilic substitution. The S l and Sj. 2 pathways involve mechanisms that are not open to aryl halides. The greater s character of the sp bond makes it more difficult to cleave the bond to generate a carbo-cation. However, these restrictions do not apply to radical or carbanion chemistry. Hence, aryl halides undergo radical coupling reactions and metal insertion reactions, leading to organometallic compounds. 

This mechanism is quite general for this substitution reaction in transition metal hydride-carbonyl complexes [52]. It is also known for intramolecular oxidative addition of a C-H bond [53], heterobimetallic elimination of methane [54], insertion of olefins [55], silylenes [56], and CO [57] into M-H bonds, extmsion of CO from metal-formyl complexes [11] and coenzyme B12- dependent rearrangements [58]. Likewise, the reduction of alkyl halides by metal hydrides often proceeds according to the ATC mechanism with both H-atom and halogen-atom transfer in the propagation steps [4, 53]. 

Substitution by the SN2 mechanism and -elimination by the E2 and Elcb mechanisms are not the only reactions that can occur at C(sp3)-X. Substitution can also occur at C(sp3)-X by the SRN1 mechanism, the elimination-addition mechanism, a one-electron transfer mechanism, and metal insertion and halogen-metal exchange reactions. An alkyl halide can also undergo a-elimination to give a carbene. 

Metallated spirobicyclicphosphoranes 96a-c were found to undergo carbonyl substitution reactions with triphenylphosphine in toluene to form (97a-c) and the isolated products were characterised by IR, H nmr, elemental analysis and thermo-gravimeteric studies. There was no evidence for insertion of CO into the pentaco-ordinate P -Mn bond. 

The difficulties of direct oxidative insertion with metals other than Mg or Li mean that o-complexes are often made from organo-lithium or Grignard reagents by metal exchange. This reaction amounts to a nucleophilic substitution at the metal without a change of oxidation state so the metal is used in whatever oxidation state is finally needed. Attack of methyl lithium on a Cu(I) halide gives methyl copper 50, a o-complex of Me- and Cu(I). If an excess of MeLi is present an ate complex is formed, lithium dimethylcuprate 51. This is formally a compound of a copper anion 51a, just as BF4 is a borate. The term ate complex refers to such formally anionic complex in which the metal has one extra anionic ligand. Its true structure is dimeric 51b and it exists as an equilibrium with 52 in solution.20... 

In general, the catalytic cycle for the transition-metal catalyzed allylic substitution reactions involves initial attack of the metal at the double bond followed by oxidative insertion into the antiperiplanar C-0 bond to afford the Ti-allyl system. At this point, depending on whether soft or hard nucleophiles are used, however, the alkylation reaction proceeds through distinctly different pathways (Scheme 10). With soft nucleophiles, where Pd is often the metal center of choice. 

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