Synthesis of a New Class of Compounds Containing a Ln−O−Al Arrangement and Their Reactions and Catalytic Properties

Synthesis of a new class of compounds containing a Ln−O−Al moiety has been accomplished
by the reaction of LAlOH(Me) (L = HC(CMeNAr)2, Ar = 2,6-iPr2C6H3) with a series of Cp3Ln compounds.
The terminal Al−OH group shows selective reactivity, and the complexes Cp2Ln(THF)−O−AlL(Me) (Ln =
Yb, 1; Er, 2; Dy, 3), Cp2Yb−O−AlL(Me) (4), and Cp3Ln(μ-OH)AlL(Me) (Ln = Er, 5; Dy, 6; Sm, 7) were
obtained. This allows further insight into the proton exchange process, and two different mechanisms,
intermolecular and intramolecular elimination of CpH, are proposed under different conditions. Complexes
1−4, 6, and 7 have been characterized by X-ray structural analyses which reveals a Ln−O−Al or Ln(μ-OH)Al core in these complexes. The obtuse Ln−O−Al angles fall in the range 151.9−169.8°. The reaction
of 1 or 4 with Me3SnF in toluene under refluxing conditions unexpectedly yielded the compounds [Cp2Yb(μ-OSnMe3)]2 (8) and LAl(Me)F (9). Reactions of LAlOH(Me) with the mono- and dicyclopentadienyl
complexes LYbCp(Cl) (10) and LYbCp2 (11) supported by the bulky β-diketiminate ligand were unsuccessful.
However, the reaction of LAl(OH)Me with LYbN(SiMe3)2Cl (12) containing a labile Yb−N bond leads to the
formation of LYbCl−O−AlL(Me) (13) under elimination of HN(SiMe3)2. Furthermore, complexes 1, 3, 4,
and 6 exhibit good catalytic activity for the polymerization of ε-caprolactone.

本研究通过LAlOH(Me)（其中L = HC(CMeNAr)₂，Ar = 2,6-二异丙基苯基（2,6-iPr₂C₆H₃））与一系列三[环戊二烯基（cyclopentadienyl, Cp）]镧系元素（lanthanide, Ln）化合物的反应，成功合成了一类含有Ln−O−Al结构单元的新型化合物。末端Al−OH基团展现出选择性反应活性，由此得到配合物Cp₂Ln(四氢呋喃（tetrahydrofuran, THF）)−O−AlL(Me)（Ln = 镱（Yb），1；铒（Er），2；镝（Dy），3）、Cp₂Yb−O−AlL(Me)（4）以及Cp₃Ln(桥联羟基（μ-hydroxo）)AlL(Me)（Ln = 铒（Er），5；镝（Dy），6；钐（Sm），7）。该研究为深入探究质子交换过程提供了重要支撑，研究人员提出了两种不同的反应机理：在不同反应条件下，分别通过分子间与分子内消除环戊二烯（cyclopentadiene, CpH）的路径进行。配合物1~4、6和7经X射线晶体结构分析（X-ray structural analyses）表征，结果表明其核心结构均为Ln−O−Al或Ln(μ-OH)Al单元，其中钝角Ln−O−Al键角范围为151.9°~169.8°。将配合物1或4与三甲基氟化锡（Me₃SnF）在甲苯中回流反应，意外得到了化合物[Cp₂Yb(μ-OSnMe₃)]₂（8）与LAl(Me)F（9）。采用位阻型β-二亚胺配体（β-diketiminate ligand）稳定的单[环戊二烯基（cyclopentadienyl, Cp）]基与二[环戊二烯基（cyclopentadienyl, Cp）]基镱配合物LYbCp(Cl)（10）和LYbCp₂（11）与LAlOH(Me)的反应并未获得成功。不过，含有易断裂Yb−N键的LYbN[(三甲基硅基（trimethylsilyl, SiMe₃）)₂]Cl（12）与LAl(OH)Me反应，在消除六甲基二硅基胺（hexamethyldisilazane, HN(SiMe₃)₂）后，成功得到了LYbCl−O−AlL(Me)（13）。此外，配合物1、3、4和6对ε-己内酯（ε-caprolactone）的聚合反应表现出优异的催化活性。