Electronegativity, transmetallation

Organic compounds M—R and hydrides M—H of main group metals such as Mg, Zn, B, Al, Sn, SI, and Hg react with A—Pd—X complexes formed by oxidative addition, and an organic group or hydride is transferred to Pd by exchange reaction of X with R or H. In other words, the alkylation of Pd takes place (eq. 9). A driving force of the reaction, which is called transmetallation, is ascribed to the difference in the electronegativities of two metals. A typical example is the phenylation of phenylpalladium iodide with phenyltributyltin to form diphenylpalladium (16). 

Direct transmetalation of organoboranes to organocopper reagents is not a general reaction. Because of dieir similar bond energies and electronegativities, diis trans-nietalation is linided to die preparation of alkenylcopper and unfiinctionalized... 

Transmetallation represents the most widely applicable method for the preparation of ZrCp2 derivatives. In view of the relatively low electronegativity (EN hereafter) of Zr (EN 1.2—1.4), however, transmetallation as shown in Scheme 1.9 may be expected to be favorable only with organometals containing highly electropositive metals, such as Li (EN 1.0) and Mg (EN 1.20). Indeed, facile and complete dialkylation of Cp2ZrCl2 may be readily observed with these metals. With organolithiums, however, the reaction... 

A smoother transmetalation procedure should be ensured by the more electronegative character of aluminium, as first demonstrated by Wipf and Ireland [35]. Thus, hydroalumination of 1-hexyne with DIBAL-H, followed by addition of the cuprate 59, bearing non-transferable alkynyl groups, provides the copper intermediate 60. This adds smoothly to 2-cyclohexenone to produce the Michael adduct 61, in 72% yield (Scheme 2.18) [36],... 

Another important class of transmetallation reactions are those involving more electronegative metals than Li and Mg, such as A1 and Zr shown in Scheme 5, as well as... 

The trend shown in Eq. (d) is representative of transmetallation reactions, and consideration of the relative carbon transferabilities based on electronegativity provides predictive power. 

The thermodynamics of the transmetallation reaction should depend largely upon electronegativity considerations the reaction should proceed to give the more metal-organic product. However, this may... 

Stannacylopentadienes (stannoles) can be prepared from butadienylhthium compounds and tin halides (equation 10-13)24 and by Sn/Li transmetallations (equation 10-14) 17 the electronegative character of the double bonds, and the ring strain, render the ate complexes unusually stable. 

Table 12-5 shows a portion of the periodic table with Pauling electronegativities listed below each element.115 Use of these electronegativity values in conjunction with equation 12.53 allows one to predict whether a particular transmetalation is favorable or unfavorable. 

A Grignard reagent will undergo transmetallation (metal exchange) if it is added to a metal halide whose metal is more electronegative than magnesium. In other words, metal exchange will occur if it results in a less polar carbon-metal bond. For example, cadmium... 

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