Nucleophiles metallated

A particularly elegant route to metallacarbor-anes is the direct oxidative insertion of a metal centre into a c/oso-carborane cluster the reaction uses zero-valent derivatives of Ni, Pd and Pt in a concerted process which involves a nett transfer of electrons from the nucleophilic metal centre to the cage ... 

Neutral transition-metal complexes that are not fully coordinatively saturated possess nucleophile metal centers capable of coordinating to electrophiles. On the other hand, group-IIIB halides serve as typical electron-pair acceptors and are, therefore, able to interact coordinatively with basic metal complexes. 

Bidentate NHC-Pd complexes have been tested as hydrogenation catalysts of cyclooctene under mild conditions (room temperature, 1 atm, ethanol). The complex 22 (Fig. 2.5), featuring abnormal carbene binding from the O carbon of the imidazole heterocycles, has stronger Pd-C jj, bonds and more nucleophilic metal centre than the bound normal carbene chelate 21. The different ligand properties are reflected in the superior activity of 22 in the hydrogenation of cyclooctene at 1-2 mol% loadings under mild conditions. The exact reasons for the reactivity difference in terms of elementary reaction steps are not clearly understood [19]. 

Other heteropolynuclear gold(II) complex that can be obtained by replacement of halide groups in bis(ylide)gold(II) species by other anionic nucleophilic metal complex is the tin derivative [Au2 Sn[N(p-Tol)SiMe2]3SiMe 2 M-(CH2)2PPh2 2] (350).2041... 

Based on a detailed investigation, it was concluded that the exceptional ability of the molybdenum compounds to promote cyclopropanation of electron-poor alkenes is not caused by intermediate nucleophilic metal carbenes, as one might assume at first glance. Rather, they seem to interfere with the reaction sequence of the uncatalyzed formation of 2-pyrazolines (Scheme 18) by preventing the 1-pyrazoline - 2-pyrazoline tautomerization from occurring. Thereby, the 1-pyrazoline has the opportunity to decompose purely thermally to cyclopropanes and formal vinylic C—H insertion products. This assumption is supported by the following facts a) Neither Mo(CO)6 nor Mo2(OAc)4 influence the rate of [3 + 2] cycloaddition of the diazocarbonyl compound to the alkene. b) Decomposition of ethyl diazoacetate is only weakly accelerated by the molybdenum compounds, c) The latter do not affect the decomposition rate of and product distribution from independently synthesized, representative 1-pyrazolines, and 2-pyrazolines are not at all decomposed in their presence at the given reaction temperature. 

To summarize briefly, our approach involves initial attack by a relatively nucleophilic metal hydride on coordinated CO. Such reactivity has been demonstrated repeatedly for main-group metal hydrides perhaps the most elegantly worked-out system involves CpRe(C0)2(N0)+ (Cp = Tl-C H ) which, under varying conditions, can be converted to an entire range of products containing CO at different stages of reduction, including formyl, carbene, hydroxymethyl and methyl species (Scheme l). Reactions lead-... 

Sn2 and SNAr Reactions In these reactions the metal atom attacks aliphatic or aromatic carbon bonded to X, respectively. A stronger nucleophilic metal as well as a better leaving group X (I>Br>Cl>F) facilitates, whereas steric hindrance in R slows these types of oxidative addition [193, 194]. SNAr reactions are favored by electron-withdrawing substituents Y in the case of the substrates 4-YQH4X [2], Sn2 [27, 29, 89, 117, 180, 181] and SNAr [31, 33, 62-67, 95, 100, 107-109] mechanisms have been suggested frequently for zerovalent d10 complexes such as [L M] (M = Ni, Pd, Pt L=tertiary phosphine =2,3,4). For example ... 

The mechanism that is consistent with biochemical, enzymological and structural data involves binding of arginine, in which the side-chain of Glu277 plays an important role, attack of the nucleophilic metal-bridged hydroxyl ion, formation of a neutral, tetrahedral intermediate which is stabilized by the dinuclear Mn(II) centre, and finally proton transfer from Hisl41, followed by release of the two products (Figure 16.5). 

An activation of the nucleophile by insertion of the transition metal species into a nucleophile-hydrogen bond. Here typical metals are Pd(0), Y(III), La(III) and Sm(III). Then one Jt-bond of the 1,2-diene in 13 inserts intramolecularly into the nucleophile-metal bond (Scheme 15.2). Depending on the regioselectivity of this insertion either 14, the possible equilibrium between 15,16,17 or 18 will be the next intermediates. Reductive elimination finally delivers 8 from 14, 10 and/or 11 from 15,16 or 17 and 12 from 18. 

Mechanistically similar to the reaction of nucleophilic metallates with a-haloimines is their reaction with amides. In this case formation of the carbene complex requires treatment with a silyl chloride (Figure 2.8) [42,125,126]. 

All synthetic methods described up to now (ligand displacement, acac or halo-methyl precursors, metal-bonded carbene + nucleophile, metal-bonded nucleophile + carbene) result in a metal-bonded ylide through the Ca atom. The reactivity of ylides toward metallic systems is, however, greater than anticipated and other reaction pathways could compete with simple C-bonding. 

The polymerization of lactones is initiated by nucleophilic metal alkoxides. It is worth noting that bulky alkoxides are not nucleophilic enough and react as bases. For example, potassium ferf-butoxide deprotonates (3-propionolactone and sCL into new anionic species, which are anionic initiators for the polymerization of lactones [8] (Fig. 4). As a rule, carboxylic salts are less nucleophilic than the corresponding alkoxides and are, in general, not efficient initiators for the polymerization of lactones. Nevertheless, (3-lactones are exceptions because their polymerization can be initiated by carboxylic salts [8]. 

Owing to their stability and low nucleophilicity, metal acetylides are less reactive toward Cjq than other lithium organyls or Grignard reagents [11]. Though the reaction is slower and higher reaction temperatures are necessary, various acetylene derivatives of Cjq could be obtained. The first acetylene Cjq hybrids were (trimethyl-silyl)ethynyl- and phenylethynyl-dihydro[60]fullerene, synthesized simultaneously... 

Nucleophilic metal alkoxide reacts rapidly with electrophilic water to generate the several hydrolysis products with complex intermediate species containing some residual alkoxy groups. The concentration ratio of the starting reagents and the nature of alkoxide and the solvent influence the morphology of hydrolysis products. Overall, the formation reaction for particles consists of hydrolysis of metal alkoxide and condensation of the hydrolysis species. The hydrolysis reaction of metal alkoxide... 

It is generally accepted that C02 is somewhat unreactive towards transition metal complexes and that the metal C02 linkage is favoured by a nucleophilic metal centre such as a tertiary phosphine metal(O) moiety. 

Nucleophilic attack on a rt-allyl ligand of a metal complex occurs in general at one of the terminal carbons to afford allylated products. The attack, however, may be directed to the central carbon atom of the 7i-allyl group to produce cyclopropyl derivatives by appropriate choice of nucleophile, metal ligand and reaction conditions (equation 33). A variety of nucleophiles (pA"a > 20) including ester and ketone enolates and a-sulfonyl carbanions react with... 

Nucleophilic metal alkylidene complexes are more useful for promoting the metathesis polymerisation of cycloolefins than electrophilic metal carbenes. For instance, Br2(Me3CCH20)2W=CHCMe3 is a moderately active catalyst [75,89] that can be further activated by the addition of Lewis acids such as GaBr3 to... 

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