Alkyl groups exchange

For example, examination of the organic products after quenching a reaction with C02 has provided evidence for alkyl group exchange between RMgX and R X. 

FIGURE 1. Proposed intermediate in alkyl group exchange. Co-ordinated solvent molecules are omitted for clarity... 

Methyl, butyl, or trimethylsilylmethyl compounds of Na, K, Rb, or Cs can be used to generate other organometallic compounds by alkyl group exchange. 

Long (81) showed that the complex from biscyclopentadienyltitanium dichloride and methylaluminum chloride or a simply derived product from it, was an active ethylene polymerization catalyst. There have been a number of attempts to determine the exact nature of initiation in polyethylene. However, by any techniques available until now, it has not been possible to determine the actual ionic nature of the active catalyst which polymerizes ethylene. Karapinka and Carrick (82) studied the polymerization of ethylene with biscyclopentadienyltitanium dichloride and various alkylaluminum compounds. They found that the alkyl group exchanged so readily between the aluminum and titanium, that the location of the initiating site could not be determined. All that could be concluded was that an ethyl group initiated the polymerization more easily than the phenyl. 

Drandarov, K. Hesse, M. Lithium and proton templated co-polyazamacrolactamization, new general routes to macrocyclic polyamines. Tetrahedron Lett. 2002, 43, 7213-7216. Murahashi, S.-L Yoshimura, N. Tsumiyama, T. Kojima, T. Catalytic alkyl group exchange reaction of primary and secondary amines. 

Another example is provided by the alkyl group exchange between the pentacoor-dinated alkyl cobalt porphyrins and tetracoordinated cobalt(II) hydroporphyrins59 that takes place readily at room temperature as observed by H NMR (Equation 8.121). 

Further evidence of possible formation of five-coordinate aluminum atoms as a pathway for exchange has been reported by Mole and co-workers (50) in a study of alkyl group exchange between trimethylaluminum and dimethylethylaluminum etherates. The exchange rate has an overall second-order dependence on total aluminum concentration and a zero-order dependence on ether concentration, indicating alkyl exchange without prior dissociation of the ether adducts. 

T1(CH3)4 may be due to the high stability of the complex formed. Further studies in this area are clearly necessary to provide details concerning alkyl group exchange and relative stabilities of compounds. 

Halogen-alkyl group exchange in Me3N BR Y3 n (R = propyl, butyl X = F,C1) also requires the presence of three-coordinate boron and a similar mechanism is probable (37). 

In these conditions, excess of R2Zn and the catalyst (transition metal) are not required. In addition, when a solution of an alkyl iodide is mixed with 1 equiv of R2Zn the mixed diorganozinc compounds (R-Zn-R ) are obtained (equation 5). This reaction takes place only between diaUcylzincs and alkyl iodides however, in comparison with the few other methods described for the preparation of mixed diorganozincs, this procedure represents a fantastic enhancement for alkyl group exchange (R-Zn-R ). ... 

The direct functionalization of sp C-H bonds in alkanes is an extremely difficult process [69[, and only a limited number of studies have been reported. A much more practical - but still challenging - process is the functionalization of sp C-H bonds adjacent to a heteroatom [70-73]. Murahashi reported the impressing example of an alkyl group exchange reaction and hydrolysis reaction of tertiary amines... 

Many organomagnesium derivatives (e.g., RMgX) undergo alkyl group exchange when treated with reactive alkanes through C-H bond insertion. Cyclopentadiene, indene, fluorene, and their derivatives are readily metallated in the absence of a diethyl ether solvenf [Eq. (6.99)] ... 

The effects of introducing halogens in the 2 and 6 position of phenyl imine catalysts was also studied in diimine pyridine iron dichloride/MAO systems [13]. These catalysts afford linear products with a low olefin content, generally less than one (olefin) functionality per chain. The latter is due to a fast transfer of iron bound alkyl groups to the aluminum compounds that are present in excess. After hydrolysis, alkanes are obtained. When a high ratio of aluminum alkyl to iron catalyst is used, polyethene waxes are obtained due to the statistically favored alkyl group exchange between the metal species. 

A simple conversion of (-I- )-a- to (-I- )-P-pinene has been effected through the addition product with 9-BBN (9-borabicyclo[3.3.1]nonane). B-3-Pinanyl-9-BBN (806) undergoes exceptionally rapid olefin-alkyl group exchange after 30 hours reflux in diglyme it has reached equilibrium, the major component being the myrtenyl derivative 807, from which (-f-)-P-pinene [(-t-)-142] is liberated with benzaldehyde. From (-I- )-a-pinene of 92% optical purity, (+ )-p-pinene of... 

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