Five different types of η8-cyclooctatetraenyl-lanthanide half-sandwich complexes from one ligand set, including a “giant neodymium wheel”?

Dalton Transactions Pub Date: 2016-06-28 DOI: 10.1039/C6DT01974A

Abstract

The lithium-cyclopropylethynylamidinates Li[c-C3H5–C[triple bond, length as m-dash]C–C(NR)2] (1a: R = iPr, 1b: R = cyclohexyl (Cy)) have been used as precursors for the preparation of five new series of half-sandwich complexes. These complexes contain the large flat cyclooctatetraenyl ligand (C8H82?, commonly abbreviated as COT), and were isolated as solvated, unsolvated and inverse sandwich complexes. Treatment of the halide precursors [(COT)Pr(μ-Cl)(THF)2]2 with 1b and [(COT)Nd(μ-Cl)(THF)2]2 with 1a and 1b in THF in a 1?:?2 molar ratio, respectively, afforded (COT)Ln[μ-c-C3H5–C[triple bond, length as m-dash]C–C(NR)2]2Li(L) (2: Ln = Pr, R = Cy, L = Et2O; 3: Ln = Nd, R = iPr, L = THF; 4: Ln = Nd, R = Cy, L = THF). Treatment of the dimeric cerium(III) bis(cyclopropylethynylamidinate) complexes [{c-C3H5–C[triple bond, length as m-dash]C–C(NR)2}2Ce(μ-Cl)(THF)]2 (5: R = iPr; 6: R = Cy) in situ with K2C8H8 in a 1?:?1 molar ratio in THF at room temperature afforded the inverse-sandwich complexes (μ–η8:η8-COT)[Ce{c-C3H5–C[triple bond, length as m-dash]C–C(NR)2}2]2 (7: R = iPr; 8: R = Cy). This reaction represents a new method for encapsulation of a planar (C8H8)2? ring in lanthanide complexes containing amidinate ligands in the outer decks. Novel unsolvated dinuclear lanthanide half-sandwich complexes were prepared by using the precursors 1a, 1b and COT2?. Unlike the complexes 2–4, the reaction of [(COT)Pr(μ-Cl)(THF)2]2 with 1a afforded the unsolvated centrosymmetric complex [(COT)Pr(μ-c-C3H5–C[triple bond, length as m-dash]C–C(NiPr)2)]2 (9). These dimeric structures could be also accessed by reaction of LnCl3 (Ln = Ce or Nd) with 1a or 1b and K2COT in a 1?:?1?:?1 molar ratio as a one-pot reaction to give novel [(COT)Ln(μ-c-C3H5–C[triple bond, length as m-dash]C–C(NR)2)]2 complexes (10: Ln = Ce, R = iPr; 11: Ln = Ce, R = Cy; 12: Ln = Nd, R = iPr). Similar treatment of HoCl3 with 1a or 1b and K2COT as three-component reactions in a 1?:?1?:?1 molar ratio afforded the solvated half-sandwich complexes (COT)Ho(c-C3H5–C[triple bond, length as m-dash]C–C(NR)2)(THF) (13: R = iPr; 14: R = Cy). A unique multidecker sandwich complex [(μ–η8:η8-COT){Nd(c-C3H5–C[triple bond, length as m-dash]C–C(NCy)2)(μ-Cl)}2]4 (15) was prepared by reaction of anhydrous NdCl3 with K2COT and 1b in a one-pot reaction. The solid state structure of 15 revealed the presence of an unprecedented macrocyclic sandwich compound (“giant neodymium wheel”) consisting of four COT rings sandwiched between eight Nd3+ ions, and each Nd3+ ion is bonded to one amidinate ligand and bridged by two chlorine atoms with the neighbouring Nd3+ ion.

Graphical abstract: Five different types of η8-cyclooctatetraenyl-lanthanide half-sandwich complexes from one ligand set, including a “giant neodymium wheel”
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