Elusive Trimethyllanthanum: Snapshots of Extensive Methyl Group Degradation in LaAl Heterobimetallic Complexes

Abstract

Reactions of [La(AlMe4)3] and [Y(AlMe4)3] with PMe3 show that the phosphine can cleave Ln--CH3--Al linkages, separating Me3Al(PMe3). PMe3 (3 mol equiv) reacts with [Y(AlMe4)3] to give [(YMe3)n] contaminated with by-products containing phosphorus and aluminum. The La-based analog, [(LaMe3)n], is not formed selectively from the reaction of [La(AlMe4)3] with PMe3 or Et2O, which rather yields insoluble La/Al heterobimetallic products. Three multi-nuclear La-based clusters were obtained from a reaction of [La(AlMe4)3] with PMe3 (1 equiv) and identified by X-ray structure analyses. Each cluster exhibits extensive methyl group degradation and contains methylene, methine, or carbide moieties. [La4Al8(CH)4(CH2)2(CH3)20(PMe3)] has a [La4(CH)4] cuboid core supported by AlMe3, Me2AlCH2AlMe2, and PMe3 ligands. [La4Al8(C)(CH)2(CH2)2(CH3)22(toluene)] also contains a cuboid core, [La3Al(C)(CH)2(CH2)], which includes one exo cubic lanthanum atom, and is supported by AlMe3, Me3AlCH2AlMe2, (AlMe4)-, and toluene ligands. The lanthanum atoms in [La5Al9(CH)6(CH3)30] are arranged in a trigonal bipyramidal fashion with (CH) functionalities capping each face. The [La5(CH)6]3- core is formally balanced by three AlMe2 + moieties and is additionally supported by six AlMe3 ligands. The unit cell contains two independent La5 clusters, one with pseudo-C3h and the other with pseudo-D3 symmetry, as well as two molecules of the separation co-product Me3Al(PMe3).

CH Activation versus Yttrium–Methyl Cation Formation from [Y(AlMe4)3] Induced by Cyclic Polynitrogen Bases: Solvent and Substituent‐Size Effects

“…[13] These results are in line with the observation that addition of the single-site Lewis base PMe 3 to [LaA C H T U N G T R E N N U N G (AlMe 4 ) 3 ] results in multiple C À H activation to afford larger aggregates, comprised of methylene, methine and carbide units. [14] The reactions of the smaller lanthanide ion reagents [YA C H T U N G T R E N N U N G (AlMe 4 A C H T U N G T R E N N U N G (AlMe 4 ) 3 ] with diethyl ether or THF in equimolar ratios has even led to the formation of polymeric trimethyls of yttrium and lutetium. [15] Recently, we have contributed a further reactivity pattern in reactions of [SmA C H T U N G T R E N N U N G (AlMe 4 ) 3 ] with the more bulky tripodal Lewis base 1,3,5-tricyclohexyl-1,3,5-triazacyclohexane (TCyTAC).…”

Eine Seltenerdmetallvariante des Tebbe‐Reagens

“…[9,10] Vorangegangene Untersuchungen unserer Arbeitsgruppe befassten sich mit Seltenerdmetall(III)-TetramethylaluminatKomplexen [L x Ln{Al(CH 3 ) 4 } y ] (y = 1, 2, 3; x + y = 3, L = einzähniger Hilfsligand, Ln = Seltenerdmetall und Sc, Y, La) als Polymerisationskatalysatoren [11,12] und führten zur Isolation von Ln III -Clustern mit Methylen-, [13,14] Methin- [15] und Carbidfunktionalitäten. [16] [14] Die Röntgenstrukturanalyse, die an den farblosen Kristallen (das Rohprodukt wurde aus einer Toluol/Hexan-Mischung kristallisiert) [21] durchgeführt wurde, bestätigte die Molekül-struktur, die auf der Grundlage VT-1 H-NMR-spektroskopischer Studien (VT = variable Temperatur) vorgeschlagen worden war (Abbildung 1). [14] In Einklang mit der ausgeprägten Mobilität des CH 3 präsentiert damit ein Strukturanalogon zum postulierten Tebbe-Intermediat B°.…”

“…[29] Eines der Methylenprotonen orientiert sich in Richtung des Lanthanzentrums, was an eine a-agostische La-(HC)-Wechselwirkung erinnert (La-H25B 2.60(3) und La-C25-H25B 84 (2)8). [30] (7) ) [16] sowie in [Cp* 3 La 3 (m-Cl) 3 (m 3 -Cl)(m 3 -CH 2 )(thf) 3 ] (2.537(3) bis 2.635(3) ) beobachtet. [13] Die beiden La-(m-CH 3 )-Bindungslängen in 3 (La-C26 2.809(2), La-C29 2.833(2) ) liegen im erwarteten Bereich.…”

Subtle Size Effects in C–H Activation Reactions of Lanthanum and Praseodymium Tetramethylaluminates by Neutral Trinitrogen Bases

“…These AlMe 3 groups show a different binding in the structures of 2a and 2b. The structure shown in Figure 2 is more asymmetrically bound in this respect, with one of the Pr-C contacts, Pr(1)-C(11), being shorter at 2.738(6) Å, whereas the other, Pr(1)-C (13), is longer at 3.169(7) Å. In contrast, the structure of 2b contains two similar Pr-C bonds, Pr(2)-C(27) and Pr(2)-C(29), which are 2.870(8) and 2.814(7) Å, respectively.…”

“…[12] Although single-site bases, such as diethyl ether, THF or PMe 3 , lead to the formation of polymeric LnMe 3 in some cases, others have been observed in which complex mixtures of highly aggregated products including degraded methyl groups in the form of CH 2 2-, CH 3-and C 4-units have been detected. [13] Better control of the products has been achieved in reactions of Y(AlMe 4 ) 3 with hydridotris(pyrazolyl)borates LH. In the case of La(AlMe 4 ) 3 this leads to [LLa(Me 3 -AlCH 2 AlMe 3 )], which contains a CH 2 2-unit formally bound to one LLa 2+ and two AlMe 3 units.…”