Metal nucleophiles

The oxidative addition of alkyl halides can proceed in different ways, although the result is usually atrans addition independent of the mechanism. In certain cases the reaction proceeds as an SN2 reaction as in organic chemistry. That is to say that the electron-rich metal nucleophile attacks the carbon atom of the alkyl halide, the halide being the leaving group. This process leads to inversion of the stereochemistry of the carbon atom (only when the carbon atom is asymmetric can this be observed). There are also examples in which racemisation occurs. This has been explained on the basis of a radical chain... 

Breslow and Chipman, 1965). The metal-nucleophile combination is quite reactive toward a coordinating substrate compared with p-nitrophenyl acetate. 

The lactone concept is not restricted to the simple model biaryl synthesis presented here. It has been successfully expanded to a broad series of structurally diverse biaryl substrates (e.g., lactones with additional stereocenters and functional groups, configurationally stable lactones, seven-membered lactones, and again configurationally unstable biaryl hydroxy aldehydes ), to different activation modes in the ring-opening step (e.g., use of metallated nucleophiles, carbonyl activation by Lewis acids, (Ti -complexation, etc.), and for various strategies of stereoselection (e.g., external vs. internal asymmetric induction). ... 

In contrast to their hydrocarbon analogues, many unsaturated fluorocarbons react with anionic transition metal nucleophiles to yield products arising from net displacement of fluoride ion. This synthetic approach has been successful in producing a host of fluorovinyl and fluoroaryl complexes (95-110). 

Examples of cyclization through alkene insertion of a metal-nucleophile intermediate (Scheme 3, intermediate F) using organolanthanide catalysts, (Cp LaHfe, have been reported recently (equation 132), although turnover numbers rather than synthetic yields were reported.263... 

A procedure for alkylation of C=0 double bonds in the presence of (metal-free) organocatalysts and non-metallic nucleophiles has been reported by the Iseki group for trifluoromethylation of aldehydes and ketones [185]. On the basis of a previous study of the Olah group [186, 187] which showed the suitability of non-chiral phase-transfer catalysts for trifluoromethylation of carbonyl compounds, Iseki et al. investigated the use of N-benzylcinchonium fluoride, 182, as a chiral catalyst. The reaction has been investigated with several aldehydes and aromatic ketones. Trifluoromethyltrimethylsilane, 181, was used as nucleophile. The reaction was, typically, performed at —78 °C with a catalytic amount (10-20 mol%) of 182, followed by subsequent hydrolysis of the siloxy compound and formation of the desired alcohols of type 183 (Scheme 6.82). 

S.5. By Reactions of Unsaturated or Weakly Stabilized Metal Complexes with Metal Nucleophiles... 

The addition of metal nucleophiles to eomplexes containing metal-metal multiple bonds is an excellent method of forming larger clusters. One of the most widely used is H20s3(CO)io ... 

Displacement of weakly coordinating ligands is also very effective. Common ligands that form weakly stabilized complexes with metals include acetonitrile, ethylene, and other mono- and diolefins. The metal nucleophile may be a metal carbonyl anion, a metal hydride, or a neutral, low-valent metal complex ... 

Attack by a metal nucleophile at a metal-carbon multiple bond, instead of an unsaturated metal-metal bond, can be used to form clusters containing two- or three-electron carbon ligands. The reaction of Pt(cyclooctadiene)2 with carbene complexes (OC)5MC(OMe)Ph gives the corresponding (OC)5M[/i2-C(OMe)Ph]Pt(cod), where M = Cr or W . Performing this reaction in the presence of PR3 gives a more stable a product ... 

Reactions of transition metal carbonyls with an In(I) center also take place by oxidative addition here InX inserts into the M-X bond. Oxidative addition to the low-valent halides of Ga, In, or T1 thus provides a useful route to compounds with group IIIB-metal bonds This approach is particularly useful when the salt elimination route cannot be employed because a suitable transition metal nucleophile is lacking. 

Ci4HOi4Re3 Re3H(CO)i4 formation 10.3.5.2 Ci4H6N20ioOS3 Os3(CO)io(CH3Cn)2 reaction with metal nucleophiles 92.5.5... 

The nucleophilic addition on substituted ketenes is a well-known method to generate a prochiral enolate that can be further protonated by a chiral source of proton. Metallic nucleophiles are used under anhydrous conditions therefore, the optically pure source of proton must be added then (often in a stoichiometric amount) to control the protonation. In the case of a protic nucleophile, an alcohol, a thiol, or an amine, the chiral inductor is usually present at the beginning of the reaction since it also catalyzes the addition of the heteroatomic nucleophile before mediating the enantioselective protonation (Scheme 7.5). The use of a chiral tertiary amine as catalyst generates a zwitterionic intermediate B by nucleophilic addition on ketene A, followed by a rapid diastereoselective protonation of the enolate to acylammonium C, and then the release of the catalyst via its substitution by the nucleophile ends this reaction sequence. 

Transition metal complexes are often very good nucleophiles and qualify as being supersoft under Pear son s HSAB classification for example, reaction with soft methyl iodide can be as much as 3 X 105 times faster than the reaction with hard methyl tosylate. Because soft nucleophiles are those with large a values in the Edwards equation, that rates for the transition metal nucleophiles are effectively correlated with oxidation potentials is not surprising. In the last chapter in this section, Chapter 16, Pearson uses recently obtained values of pKa for transition metal complexes to test the full Edwards... 

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