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Theoretical Study of the Intrinsic Reactivities of Various Allylmetals toward Carbonyls and Water

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journal contribution
posted on 28.03.2005, 00:00 by Lung Wa Chung, Tak Hang Chan, Yun-Dong Wu
Quantum mechanics MP2/6-31+G* calculations have been carried out for the reactions of a series of monomeric allylmetals with water and carbonyl compounds in the gas phase. Allyl complexes of groups IA and IIA and low-valent group IIIA and IVA metals are π-complexes or reactive σ-complexes. They show high reactivities toward hydrolysis. Group IIB, trivalent group IIIA, tetravalent group IVA, and both tri- and pentavalent group VA metals form σ-complexes with allyl. These allylmetals are less reactive toward hydrolysis than toward allylation. The calculated intrinsic kinetic preference of allylation over hydrolysis is found to correlate well with the reactivity of hydrolysis, the nucleophilicity of the allylmetals, and the lateness of hydrolysis transition structures. Both the nucleophilicity of the allylmetal complexes and the thermodynamic driving force are important to the reactivity of hydrolysis. Importantly, there is a large thermodynamic preference for allylation over hydrolysis for all allylmetals because the hydrolysis has to break a strong O−H bond. Thus, the kinetic preference for allylation is correlated with the degree of H−O bond breaking in the hydrolysis transition structure.