Kinetic studies on the reaction of (η5-MeCp) Mn(CO)2(THF) with PR3(R=Me, OEt, C6H5)

초록

The solventometal carbonyl complex, (η 5-MeCp)Mn(CO)<inf>2</inf>(THF) was found to undergo a dissociative ligand substitution reaction with PR<inf>3</inf> (R=Me, OEt, C<inf>6</inf>H<inf>5</inf>), in THF at rather low temperatures (0 °C up to 20 °C) under the pseudo-first-order reaction conditions (usually 10-fold excess of PR<inf>3</inf> with respect to the solventometal carbonyl complex concentrations) where the coordinating solvent, THF is displaced by PR<inf>3</inf>. This substitution reaction follows overall first order dependence on [(η 5-MeCp)Mn(CO)<inf>2</inf>(THF)]; therefore, the positive entropy change of activation (ΔS≠ = 2.3 e.u. for PMe<inf>3</inf>; ΔS≠=11.64 e.u. for P(OEt)<inf>3</inf>; ΔS≠ =10.52 e.u. for P(C<inf>6</inf>H<inf>5</inf>)<inf>3</inf>), together with the similar enthalpy change of activations (ΔH≠=20.52 (kcal/mol) for PMe<inf>3</inf>; ΔH≠=23.49 (kcal/mol) for P(OEt)<inf>3</inf>; ΔH≠=23.10 (kcal/mol) for P(C<inf>6</inf>H<inf>5</inf>)<inf>3</inf>) is likely to ensure the possible intermediate, (η5-MeCp)Mn(CO)<inf>2</inf>, which on reaction with PR<inf>3</inf>, transforms to the product, (η 5-MeCp) Mn(CO)<inf>2</inf>(PR<inf>3</inf>). However, in case the reaction temperature is raised up to 30 °C, this reaction is no longer dependent solely on the solventometal carbonyl complex concentration. The reacti'on rate is assumed to be more or less related to the PR<inf>3</inf> concentration. Therefore, in this case, there is some possibilily of a mechanistic reaction change from the dissociative character toward the associative one.

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