One ligand fits all: lanthanide and actinide sandwich complexes comprising the 1,4-bis(trimethylsilyl)cyclooctatetraenyl (=COT′′) ligand

Abstract

The series of anionic lanthanide(III) sandwich complexes of the type [Ln(COT 00 ) 2 ] À (COT 00 = 1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion) has been largely extended by the synthesis of eight new derivatives ranging from lanthanum to lutetium. The new compounds [Li(DME) 3 ][Ln(COT 00 ) 2 ] (Ln = Y (1), La (2), Pr (3), Gd (4), Tm (6), Lu (8)) and [Li(THF) 4 ][Ln(COT 00 ) 2 ] (Ln = Ho (5), Tm (7)) were prepared in good yields following a straightforward synthetic protocol which involves the treatment of LnCl 3 with 2 equiv. of in situprepared Li 2 COT 00 in either DME (=1,2-dimethoxyethane) or THF. The neutral actinide sandwich complexes An(COT 00 ) 2 (An = Th (9), U (10)) and An(COT 0 0 0 ) 2 (COT 0 0 0 = 1,3,6-tris(trimethylsilyl)cyclooctatetraenyl dianion; An = Th (11), U (12)) were synthesized in a similar manner, starting from ThCl 4 or UCl 4 , respectively. The COT 00 ligand imparts excellent solubility even in low-polar solvents as well as excellent crystallinity to all new compounds studied. All twelve new f-element sandwich complexes have been structurally authenticated by single-crystal X-ray diffraction. All are nearly perfect sandwich complexes with little deviation from the coplanar arrangement of the substituted COT 00 rings. Surprisingly, all six [Li(DME) 3 ][Ln(COT 00 ) 2 ] complexes covering the entire range of Ln 3+ ionic radii from La 3+ to Lu 3+ are isostructural (space group P % 1).Compound 10 is the first uranocene derivative for which 13 C NMR data are reported.

Lanthanide(III) Sandwich and Half‐Sandwich Complexes with Bulky Cyclooctatetraenyl Ligands: Synthesis, Structures, and Magnetic Properties

“…For the same reason, the Ln–centroid(COT′′) distances decrease on going from Pr [201.56(1) pm] to Tb [191.49(2) and 192.16(2) pm] to Yb [184.74(4) pm]. These values are consistent with those observed in previously described [Ln(COT) 2 ] – ‐type complexes, and particularly the similarity between 1 and its DME‐solvated analogue [Li(DME) 3 ][Pr(COT′′) 2 ] [Pr–centroid(COT′′) 202.0 pm, COT′′–Pr–COT′′ 175.80°] illustrates that the nature of the cation has virtually no influence on the structure of the complex anion . Even in the previously described DME‐depleted polymeric Tb complex [{Li(DME)Tb(COT′′) 2 } n ] [Tb–centroid(COT′′) 191.2(2) and 191.9(2) pm, COT′′–Tb–COT′′ 179.0(2)°] comprising direct Li–COT′′ contacts, the bonding parameters of the Tb atom are very similar to those of 2 .…”

“…The same applies to the [Li(TMEDA) 2 ] + salt of the ytterbium complex 3 (space group C 2/ c , monoclinic; Figure ), whereas the molecule ions are nonsymmetric in the case of the DME‐solvated terbium compound [Li(DME) 3 ] + [Tb(COT′′) 2 ] – (space group P 1, triclinic; 2 ; Figure ). The latter is isotypic with numerous previously explored [Li(DME) 3 ][Ln(COT′′) 2 ] salts , . The lanthanide ions in 1 – 3 adopt an almost linear coordination by two highly symmetrically coordinated η 8 ‐COT′′ ligands that resembles the structures of other anionic lanthanide sandwich complexes with COT‐derived ligands , .…”

“…The latter is isotypic with numerous previously explored [Li(DME) 3 ][Ln(COT′′) 2 ] salts , . The lanthanide ions in 1 – 3 adopt an almost linear coordination by two highly symmetrically coordinated η 8 ‐COT′′ ligands that resembles the structures of other anionic lanthanide sandwich complexes with COT‐derived ligands , . The deviation from an ideal linear coordination declines on going from Pr [172.507(2)°] to Tb [176.18(2)°] to Yb [177.81(1)°], which might be a consequence of the decreasing radius of the Ln 3+ ions in this direction.…”

“…Anionic sandwich complexes of the type [Ln(COT′′) 2 ] – have already been reported for various members of the lanthanide series , . Most of them have been isolated as crystalline salts with either [Li(THF) 4 ] + or [Li(DME) 3 ] + , although differently solvated species such as [Li(THF)(DME)Dy(COT′′) 2 ] and Li(DME)[Tb(COT′′) 2 ] have also been described.…”

“…It has been demonstrated that the use of the (COT′′) 2– ligand leads to improved solubility and crystallinity as compared with related lanthanide and actinide complexes of the parent COT 2– dianion. For example, well‐crystallized anionic sandwich complexes of the type [Ln(COT′′) 2 ] – have been reported for almost the entire lanthanide series , . These anionic species are interesting precursors as they can undergo clean redox reactions with anhydrous CoCl 2 with the formation of the linear, homoleptic triple‐decker sandwich complexes [Ln 2 (COT′′) 3 ].…”