THF Exchange and Molecular Dynamics in the Series (BDI)MgX(THF), Where X = Bun, NEt2, and OBut and BDI = 2-[(2,6-Diisopropylphenyl)amino]-4-[(2,6-diisopr

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• 作者：Malcolm H. Chisholm ; Kittisak Choojun ; Albert S. Chow ; Gideon Fraenkel ; Judith C. Gallucci
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：October 7, 2013
• 年：2013
• 卷：52
• 期：19
• 页码：11302-11310
• 全文大小：432K
• 年卷期：v.52,no.19(October 7, 2013)
• ISSN：1520-510X

文摘

The complexes (BDI)MgX(THF), where X = Buⁿ, NEt₂, and OBu^t, are shown to undergo THF exchange at low added concentrations of THF by a dissociative mechanism: X = Buⁿ, 螖H^# (kcal mol^鈥?) = 13.4 卤 0.4 and 螖S^# (cal mol^鈥? K^鈥?) = 6.3 卤 1.6; X = NEt₂, 螖H^# (kcal mol^鈥?) = 15.2 卤 0.5 and 螖S^# (cal mol^鈥? K^鈥?) = 11.4 卤 2.3; X = OBu^t, 螖H^# (kcal mol^鈥?) = 16.4 卤 0.3 and 螖S^# (cal mol^鈥? K^鈥?) = 9.5 卤 1.3. The apparent aryl group rotations involving the BDI ligands have, within experimental error, the same activation parameters as the THF dissociation, which suggests that the two are correlated involving a three coordinate reactive intermediate akin to what is well-known for related (BDI)ZnR compounds involving three-coordinate trigonal planar Zn²⁺. At higher concentrations of THF for X = Buⁿ and OBu^t, but not for X = NEt₂, the coalescence temperatures for apparent aryl group rotation are depressed from those of the pure compounds in toluene-d₈, and evidence is presented that this correlates with an associative interchange process which becomes dominant in neat THF. We estimate the I_a mechanism to have activation parameters: 螖H^# (kcal mol^鈥?) = 5.4 卤 0.1 and 螖S^# (cal mol^鈥? K^鈥?) = 鈭?0.9 卤 0.3 for X = Buⁿ and 螖H^# (kcal mol^鈥?) = 8.3 卤 0.8 and 螖S^# (cal mol^鈥? K^鈥?) = 鈭?9.8 卤 3.0 for X = OBu^t. For the complex (BDI)MgBuⁿ(2-MeTHF), the dissociative exchange with added 2-MeTHF occurs more readily than for its THF analogue, as expected for the more sterically demanding Lewis base O-donor: 螖H^# (kcal mol^鈥?) = 12.8 卤 0.5 and 螖S^# (cal mol^鈥? K^鈥?) = 8.6 卤 1.8. At very low temperatures in toluene-d₈, restricted rotation about the Mg鈥揙(THF) bond is observed for the complexes where X = NEt₂ and OBu^t but not for the complex where X = Buⁿ. These observations, which have been determined from dynamic NMR studies, are correlated with the reactivities of these complexes in solution.