Cyclopentadienyl Behavior of Pyrrolyl Anions within the <i>meso</i>-Octaethylporphyrinogen-Binding Lanthanides: Carbon−Hydrogen and Metal−Carbon Bond Rearrangements

The complexation of Ln(III) ions by the meso-octaethylporphyrinogen [Et8N4H4], 1, has been achieved by reacting the sodium derivative [Et8N4Na4·THF3], 2, with [LnCl3·THF2]. Depending on the reaction or crystallization solvent, a variety of structural categories of Ln−porphyrinogen complexes have been isolated and structurally characterized. When the reaction was carried out in THF and the final complex recrystallized from THF, [{(η5:η1:η5:η1-Et8N4)Ln(THF)}-η3-Na(THF)2] complexes [Ln = Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Yb (8)] were obtained in a monomeric form. When their recrystallization was performed in dioxane, a dimerization occurred thanks to dioxane bridging the sodium cations of the monomeric units [{(η5:η1:η5:η1-Et8N4)Ln(DME)}-η3-Na](dioxane)1.5] [Ln = Nd, 14; Ln = Sm, 15]. In a third category we isolated complexes where two monomeric monoanions [(η5:η1:η5:η1-Et8N4)Ln]- are η2:η3 sandwiching two sodium cations, which are exclusively solvated by the pyrrolyl anions [{(η5:η1:η5:η1-Et8N4)Ln}2-η2:η3-Na2] [Ln = Pr, 16; Ln = Sm, 17]. The three classes of compounds mentioned above, all of them containing the monomeric unit [Ln−porphyrinogen−Na], are characterized by the following structural parameters: Ln−η5(pyrrole)av, 2.490(7) Å for 7, 2.556(2) Å for 14, 2.543(2) Å for 16; Ln−η1(pyrrole)av, 2.43(1) Å for 7, 2.494(4) Å for 14, 2.485(4) Å for 16; centroid−Ln−centroid, 174.6(3)° for 7, 168.1(1)° for 14, 169.7(2)° for 16; Na−η3(pyrrole), 2.50(1) Å for 7, 2.515(3) Å for 14. The recrystallization of complexes 3−8 from DME led to dimeric organometallic complexes, where the dimerization has been via the desolvation of the Ln ion and the formation of a Ln−C σ bond with the β-carbon of a pyrrole of an adjacent Ln−porphyrinogen unit. Such dimers occur in the ion-separated form [(η5:η1:η5:η1-Et8N4)2Ln2][NaSn]2 [Ln = Pr (9), Nd (10), Sm (11), Gd (12), Eu (13)]. Their recrystallization from THF led to the ion-pair derivatives in which two sodium cations are η2-bonded to the η1-pyrrolyl anions of the dimer [{(η5:η1:η5:η1-Et8N4)2Ln2}-η2(NaSn)2] [Ln = Pr (18), Nd (19), Sm (20), Gd (21); S = DME, THF; n = 2]. When the crystallization of 9−13 was carried out from THF/dioxane, polymeric structures were isolated, where cations are bridged by dioxane molecules [{(η5:η1:η5:η1-Et8N4)2Ln}2-η2{Na(THF)}2(μ-dioxane)][Ln = Nd, 22; Ln = Gd, 23]. In the three classes made up from the dimeric building block, the structural leit-motiv is constant and two structural parameters are very close [Ln−η5(pyrrole)av, 2.538(3) Å for 11, 2.578(1) Å for 18; centroid−Ln−centroid, 172.3(2)° for 11, 170.4(1)° for 18; Ln−C, 2.471(7) Å for 11, 2.512(2) Å for 18].