Dialkylzinc compounds enthalpies

Experimental and estimated thermodynamic data of homoleptic dialkylzinc compounds are listed in Table 3. Like many organometallic compounds, the lower dialkylzincs have a positive enthalpy of formation, and only the incorporation of silicon atoms in the /3-position imparts significant thermodynamic stability. The mean Zn-C bond rupture enthalpies, all of which are quite low, follow a similar trend as the bond lengths in these compounds. Thus, the presence of methyl substituents in the a-position weakens the zinc-carbon bonds, while silyl substituents strengthen them. 

TABLE 1. Enthalpies of vaporization of dialkylzinc compounds (kJmol )... 

Much of the enthalpy of formation data for the dialkylzincs was reported from two separate sources in 1949 . From these measurements each group derived the mean bond dissociation energies of the diaUcylzinc compounds. From Reference 12, the mean C—Zn bond energies were 172 kJmor for MeaZn and 150 kJmoU for EtaZn (and by assumption for the n-Pr2Zn and n-Bu2Zn species also). From Reference 18, the mean bond energies for the MeiZn and Et2Zn compounds were reported as 171 and 144 kJmoU, respectively. 

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