Bent vs Linear Metallocenes Involving C₅Me₅ vs C₈H₈ Ligands:  Synthesis, Structure, and Reactivity of the Triple-Decked (C₅Me₅)(THF)_xSm(C₈H₈)Sm(THF)_x(C₅Me₅) (x = 0, 1) Complexes Including a Formal Two-Electron Oxidative Addition to a Single Lanthanide Metal Center¹

Abstract

A new series of bimetallic triple-decked organometallic sandwich complexes involving Sm(II) can be prepared by reacting [(C5Me4R)Sm(μ-I)(THF)2]2 with 1 equiv of K2C8H8 in toluene to form [(C5Me4R)Sm(THF)]2(μ-η8:η8-C8H8) (R = Me, 1; R = Et, 2). The diglyme ([MeOCH2CH2]2O) adduct of 1, {[(C5Me5)Sm(diglyme)]2(μ-η8:η8-C8H8)}(THF)2 (3) crystallizes from THF with a bridging (C8H8)2- dianion sandwiched between two [(C5Me5)Sm(diglyme)]+ cations with a 137.6° (C5Me5 ring centroid)−Sm−(C8H8 ring centroid) angle. This bent triple-decked metallocene has 2.91(2) Å Sm−C(C5Me5) and 2.96(5) Å Sm−C(C8H8) average distances. 1 and 2 can be desolvated at 30−50 °C under high vacuum over several hours to yield [(C5Me4R)Sm]2(μ-η8:η8-C8H8) (R = Me, 4; R = Et, 5). It was of interest to determine if 4 and 5 had triple-decked metallocene structures with three parallel rings since previously characterized bis(cyclooctatetraenyl) lanthanide and actinide complexes such as uranocene, (C8H8)2U, and [(C8H8)2Ce]- have parallel rings whereas (C5Me5)2Sm is bent. Complex 4 is found to crystallize from toluene with a structure that retains the bent geometry of 3 with 149.3° and 148.9° (C5Me5 ring centroid)−Sm−(C8H8 ring centroid) angles. 5 crystallizes from toluene with a similar bent triple-decked metallocene structure with 157.6° (C5Me5 ring centroid)−Sm−(C8H8 ring centroid) angles. The ethyl groups in 5 are oriented toward the metal center with 3.40 Å Sm···C(CH2 CH3) distances. Complexes 1 and 2 each do two-electron reductions of 1,3,5,7-C8H8 to form (C5Me4R)Sm(C8H8)(THF); 4 and 5 react similarly with 1,3,5,7-C8H8 to form (C5Me4R)Sm(C8H8). A two-electron reduction of C5Me5Cl by 1 generates (C5Me5)Sm(C8H8)(THF) and (C5Me5)2SmCl(THF), a product in which C5Me5Cl has been added to a single (C5Me5)Sm(THF) unit in 1.

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

“…(COT)-LnI(thf) 3 (1a-c) [9] were synthesized according to literature procedures. 1 [(COT)La(µ-I)(thf) 2 ] 2 (2): 1a (75 mg, 0.13 mmol) was suspended in toluene (4 mL), and 4 equiv. of AlMe 3 (37 mg, 0.51 mmol) was added.…”

“…The NMR spectra were recorded in deuterated benzene, and a small amount of thf was added to increase the solubility. 1 …”

“…[1,2] Unfortunately, the synthesis and isolation of COT rare-earth metal precursors/ complexes is often affected by side-product formation, with the Ln-COT fragment being increasingly prone to ate complexation and extensive ligand redistribution. [3] Additionally, the planar 10π-e -system can bind a metal atom to each of the two faces of the arene in an inverse sandwich fashion.…”

“…[3] Additionally, the planar 10π-e -system can bind a metal atom to each of the two faces of the arene in an inverse sandwich fashion. [1,2,4] Dimeric [(COT)Ln(µ-Cl)(thf) 2 ] 2 , which is easily accessible by reaction of anhydrous LnCl 3 with K 2 [C 8 H 8 ] in thf, is commonly used as a synthesis precursor in cyclooctatetraenyl rare-earth metal chemistry. Its utilization in salt metathesis reactions is, however, impaired by poor solubility (even in thf), formation of alkali-metal-incorporated products, and extensive complex degradation due to loss of thf.…”

Cleavage of the SnSn Multiple Bond in a Distannyne by Cyclooctatetraene: Formation of the π‐Bound Inverse Sandwich Complex [(Ar′Sn)2(μ2‐η2:η3‐cot)]

“…We present here studies of the reaction of 1 with cyclic polyolefinic molecules, in particular cyclooctatetraene (cot), 1,5‐cyclooctadiene (cod), 1,4‐cyclohexadiene and cyclohexene, and show that the reaction with cot results in the complete cleavage of the SnSn bond to give a new inverse‐sandwich structure composed of mono aryl–stannyl units and a planar C 8 H 8 ring. These types of cot‐bridged molecules are known for f‐block14–17 and s‐block elements,18, 19 whereas transition metal analogues isolated to date display olefinic or “semi‐aromatic” cot character 20–23. The inverse sandwich coordination archetype is unknown for cot derivatives of the p‐block elements and no π‐coordinated cot 2− complex of a p‐block element has been characterized.…”