Ligand Influence on the
Redox Chemistry of Organosamarium
Complexes: Experimental and Theoretical Studies of the Reactions of
(C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>Sm(THF)<sub>2</sub> and (C<sub>4</sub>Me<sub>4</sub>P)<sub>2</sub>Sm with Pyridine and Acridine
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Abstract
The reactions of the samarium(II) complexes Tmp<sub>2</sub>Sm (Tmp
= 2,3,4,5-tetramethyl-1<i>H</i>-phosphol-1-yl) and Cp*<sub>2</sub>Sm(THF)<sub>2</sub> (Cp* = 1,2,3,4,5-tetramethyl-2,4-cyclopentadien-1-yl)
with pyridine were found to be different, despite the fact that the
Cp* and Tmp π-ligands are similar in size. With Tmp<sub>2</sub>Sm, a simple adduct, Tmp<sub>2</sub>Sm(pyridine)<sub>2</sub> is isolated,
while with Cp*<sub>2</sub>Sm(THF)<sub>2</sub> pyridine is dimerized
with concomitant oxidation of samarium to form [Cp*<sub>2</sub>Sm(C<sub>5</sub>H<sub>5</sub>N)]<sub>2</sub>[μ-(NC<sub>5</sub>H<sub>5</sub>–C<sub>5</sub>H<sub>5</sub>N)]. However, reaction of
Tmp<sub>2</sub>Sm with acridine, a better π-acceptor than pyridine,
did result in acridine dimerization and the isolation of [Tmp<sub>2</sub>Sm]<sub>2</sub>[μ-(NC<sub>13</sub>H<sub>9</sub>–C<sub>13</sub>H<sub>9</sub>N)]. DFT calculations on the model structures
of Tmp<sub>2</sub>Sm and Cp*<sub>2</sub>Sm, and on the single electron
transfer step from Sm to pyridine and acridine in these ligand environments,
confirmed that, even though the Sm−π-ligand bonds are
mostly ionic, the different electronic properties of the Tmp ligand
versus that of Cp are responsible for the difference in reactivity
of Tmp<sub>2</sub>Sm and Cp*<sub>2</sub>Sm
