A Surprising Solvent Effect on the Crystal Structure of an Anionic Lanthanide Sandwich Complex

Abstract

An unusual solVent effect on the crystallization of an anionic lanthanide sandwich complex has been discoVered, demonstrating how small changes can make big differences when crystallizing organometallic compounds. Crystallization of Li(DME)Tb(COT′′) 2 (1) from toluene leads to the formation of supramolecular [Li(DME)Tb(COT′′) 2 ] n (1a), while monomeric Li(DME)Tb(COT′′) 2 (1b) is formed upon crystallization from pentane, which is intercalated in the crystal structure of the latter.In organometallic chemistry, crystallization of new compounds from organic solvents is the method of choice for growing X-ray quality single crystals. However, given the vast range of organic solvents with different polarity, the right choice is not always easy. When typical donor solvents such as THF or 1,2-dimethoxyethane () DME) are employed, coordinative interaction with a metal center is frequently encountered. Thus, it is generally accepted that in such cases different crystal structures could arise as compared to crystallization from nonpolar solvents. In the case of nonpolar hydrocarbon solvents, especially hydrocarbons, there are of course significant differences between aromatic and aliphatic hydrocarbons. Quite frequently, one type of hydrocarbon solvent (e.g., toluene) yields suitable crystals while the other (e.g., n-pentane) does not or vice versa. However, one would not expect the formation of different crystalline forms when switching between these different nonpolar hydrocarbon solvents. We report here such an unusual solvent effect on the crystallization of an anionic lanthanide sandwich complex. The work reported here provides a fascinating example of how small changes can have big effects on crystal structure and coordination mode.The compound in question is Li(DME)Tb(COT′′) 2 (1), a formally anionic lanthanide sandwich complex containing bulky cyclooctatetraenyl ligands. The organometallic chemistry of the rare earth elements continues to be a highly attractive field of research, in particular due to the numerous applications of organolanthanides in catalysis 1 and organic synthesis. 2 An increasingly important area focuses on the development of noncyclopentadienyl organolanthanide complexes. 3 Here, cyclooctatetraenyl ligands () COT) play an important role because the large, flat COT dianions are ideally suited to form sandwich complexes of the rare earth metals. 4 Long known and well established are the anionic lanthanide(III) sandwich complexes M[Ln(COT) 2 ] (M ) alkaline metal). 4a,5 More recently, bulky organosilyl-substituted COT ligands such as the 1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion () COT′′) have become increasingly popular. 6 Anionic sandwich complexes of the type [Li(THF) 4 ]-[Ln(COT′′) 2 ] (Ln ) Ce, Pr, Sm, Y) are formed upon treatment † Dedicated to Professor Rudolf Hoppe on the occasion on his 85th birthday.(1) (a) Yasuda, H.

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

“…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. As mentioned above, these complexes are key precursors for the preparation of the homoleptic triple‐decker sandwich complexes [Ln 2 (COT′′) 3 ] .…”

“…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 . In contrast, one of the two Tb–COT′′ separations is significantly reduced in the monomeric analogue [Li(DME)Tb(COT′′) 2 ] [Tb–centroid(COT′′) 186.5(2) and 196.6(2) pm, COT′′–Tb–COT′′ 176.6(9)°] …”

A Structurally Characterized Organometallic Plutonium(IV) Complex

“…[55] 1,4-Substitution was also found in all previously reported lanthanide half-sandwich and sandwich complexes [(1,4-COT'')Ln(m-Cl)(THF)] 2 ,[ Li(THF) 4 ][Ln(1,4-COT'') 2 ], and [Li(DME) 3 ][Ln(1,4-COT'') 2 ], as well as in the triple-decker sandwich complexes Ln 2 (1,4-COT'') 3 (Ln = Nd, Dy, Er). [46,[48][49][50][51][52][56][57][58] However,t here are af ew remarkable reports in the literature that indicate the triorganosilyl groups in these bulky bis(silylated) COTl igands can migrate under certain conditions;t hus far, this process is not fully understood. For example,t he first case of silyl group migration to the 1,3positions was observed when the very bulky 1,4-bis(triphenylsilyl)cyclooctatetraenyl dianion (COT BIG )w as employed as al igand in cerium sandwich complexes.S urprisingly, oxidation of the anionic cerium(III) sandwich [Li(DME) 2 ]-[Ce(1,4-COT BIG ) 2 ]w ith AgI resulted in formation of the neutral cerocene Ce(1,3-COT BIG ) 2 .…”

Rare‐Earth Metal Bis(dimethylsilyl)amide Complexes Supported by Cyclooctatetraenyl Ligands

“…[11][12][13][14] For example, salt metathetic ex- Figure 1. Structurally characterized COT lanthanide(III) alkali metal complexes A, [5,15,16] B, [6,11,[17][18][19] C, [6,[20][21][22] D, [23] E, [24][25][26] F, [25] G, [27] H, [7] I, [11] K, [6] L, [28] M, [29] N, [30] O, [31] P. [31] Eur. J. and formation of compound R (Figure 2) was achieved straightforwardly.…”