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KMID : 1059520080520050476
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Journal of the Korean Chemical Society
2008 Volume.52 No. 5 p.476 ~ p.481
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Kinetic Studies on the Reaction of (η5-MeCp)Mn(CO)2(THF) with PR3 (R=Me, OEt, C6H5)
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Kim Sang-Hyuck
Yoo Min
Park Sung-Kuk
Lee Do-Hyung
Yun Dong-Shin
Kim Jin-Ho
Park Yong-Kwang
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Abstract
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The solventometal carbonyl complex, (η5-MeCp)Mn(CO)2(THF) was found to undergo a dissociative ligand substitution reaction with PR3 (R=Me, OEt, C6H5) in THF at rather low temperatures (0℃ up to 20℃) under the pseudo-first-order reaction conditions (usually 10-fold excess of PR3 with respect to the solventometal carbonyl complex concentrations) where the coordinating solvent, THF is displaced by PR3. This substitution reaction follows overall first order dependence on [(η5-MeCp)Mn(CO)2(THF)]; therefore, the positive entropy change of activation (△S≠= 2.3 e.u. for PMe3; △S≠=11.64 e.u. for P(OEt)3; △S≠=10.52 e.u. for P(C6H5)3), together with the similar enthalpy change of activations( △H≠=20.52 (kcal/mol) for PMe3; △H≠=23.49 (kcal/mol) for P(OEt)3; △H≠=23.10 (kcal/mol) for P(C6H5)3) is likely to ensure the possible intermediate, (η5-MeCp)Mn(CO)2, which on reaction with PR3, transforms to the product, (η5-MeCp)Mn(CO)2(PR3). However, in case the reaction temperature is raised up to 30℃, this reaction is no longer dependent solely on the solventometal carbonyl complex concentration. The reaction rate is assumed to be more or less related to the PR3 concentration. Therefore, in this case, there is some possibility of a mechanistic reaction change from the dissociative character toward the associative one.
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KEYWORD
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Ligand Substitution, Solventometal Carbonyl Complex, Kinetic Study
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