LaAl3Et12: a homoleptic ethyllanthanum complex.
LaAl3Et12: a homoleptic ethyllanthanum complex.
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LaAl3Et12：均配乙基镧配合物
DOI：
10.1002/anie.201105251
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发表时间：
2011
影响因子：
--
通讯作者：
R. Anwander
中科院分区：
文献类型：
--
作者：
H. M. Dietrich;K. W. Törnroos;R. Anwander
“根据任何标准，简单的过渡金属烷基都非常不稳定。[1]Parshall和Mrowca在1968年的这个非常一般的陈述当然没有区分热力学和动力学因素，但它仍然是正确的。特别是指最简单的烷基配体甲基和乙基，后者的后过渡金属络合物被认为是非常不稳定的，因为它们倾向于通过β-H消除而分解。[2]相比之下，d0配合物似乎在β-H消除方面是动力学稳定的，这在基于早期过渡金属的齐格勒-纳塔聚合催化中是非常重要的。[3]在这方面，乙基铝试剂通过乙基转移活化过渡金属中心而作为助催化剂发挥主要作用。[4]与其甲基同系物相比，乙基铝试剂被认为是有益的，1）因为它们的合成相对具有成本效益，2）因为它们意味着更高的溶解度，和3）因此通常增强聚合活性。[5]不幸的是，早期过渡金属（包括稀土金属）的乙基络合物参与进一步的降解反应，如α-和β-氢提取以及β-烷基转移所示，特别是在不存在稳定辅助配体的情况下。[6]迄今为止，只有少量的稀土均三乙基配合物已通过X-射线结构分析进行了鉴定，而甲基衍生物显然主导了Ln-Al双齐格勒催化领域。[7]对于钪，N-供给辅助配体显示出稳定二乙基络合物，例如[{ArNC-（tBu）CHC（tBu）NAr} ScEt2]（Ar = C6H3iPr2 - 2，6）[8]和[{N（SiMe2CH2PiPr2）2} ScEt2]，[9]，而乙基格氏试剂用于盐复分解方案。通过乙烯插入反应，得到单乙基配合物[（dadmb）YEt（thf）2]（dadmb = 2，2 ′-双-[（叔丁基二甲基硅基）氨基]-6，6 ′-二甲基联苯）[10]和[Lu（μ-Et）（μ-H）{μ-Et2Si（C5H4）（C5Me4）} 2Lu][11]。四乙基铝酸酯（AlEt4）双金属基团在与二价稀土金属阳离子结合时似乎相当稳定，如均配络合物[Ln（AlEt4）2] n（Ln = Eu，Sm，Yb）所示，[12]其容易形成单体供体加合物，例如[Ln（AlEt4）2（thf）2]（Ln = Yb，Sm）。[13]Ln III四乙基铝酸盐配合物是稀缺的，可能是因为它们显示的反应性行为让人想起[LnEt（AlEt3）]（"伪装的乙基"），与本质上不稳定的第4族同系物非常相似。[14]只有混配金属茂络合物[（C5Me5）2Sm（AlEt4）]、[15][（C5Me5）2Sm-（AlEt4）（thf）]、[16]和外消旋-[{Me2Si-（AlEt4）（thf）]，（2-Me-C9H5）2} Y-（AlEt3Me）][17]和羧酸镧[（2，4，6-iPrC6H2CO2AlEt3）2La（AlEt4）][18]进行了X射线衍射分析。四乙基铝酸酯1，并详细说明其在溶液中通过β-H转移和乙烷形成的热分解，如通过NMR光谱检测的。先前对[La（AlEt4）3]（1）进行X射线晶体学分析的尝试仅产生了连接结构[19]，这是由于未优化的反应方案和1的部分分解导致的晶体质量低。我们现在已经重新研究了1的合成，用过量的AlEt3处理[La（NMe2）3-（LiCl）3]而不是[La {N（SiHMe2）2} 3（thf）2]，这使得能够容易地分离副产物[（Et2AlNMe2）2]，从而允许以良好的产率分离纯材料。在408 ℃下，从正己烷中可以得到羽毛状的高度孪晶的配合物1晶体。在相同的条件下，这些晶体在热处理过程中转变为有序的透明块体。
“By any criterion, simple transition metal alkyls are very unstable”.[1] This very general statement by Parshall and Mrowca in 1968 certainly does not differentiate between thermodynamic and kinetic factors, but it holds true nonetheless. Specifically referring to the simplest alkyl ligands methyl and ethyl, late-transition-metal complexes of the latter are considered exceedingly unstable owing to their propensity to decompose by β-H elimination.[2] In contrast, d0 complexes seem to be kinetically stabilized with respect to β-H elimination, which is of major importance in early-transition-metal-based Ziegler–Natta polymerization catalysis.[3] In this regard, ethylaluminum reagents play a major role as cocatalysts by activating the transition-metal center by ethylgroup transfer.[4] Compared to their methyl congeners ethylaluminum reagents are considered beneficial 1) because of their relatively cost-effective synthesis, 2) because they imply higher solubility, and 3) therefore often enhance polymerization activity.[5] Unfortunately, ethyl complexes of the early transition metals, including the rare-earth metals, engage in further degradation reactions, as shown for α-and β-hydrogen abstraction as well as β-alkyl transfer, particularly in the absence of stabilizing ancillary ligands.[6] To date, only a small number of rare-earth homometallic ethyl complexes has been authenticated by X-ray structure analysis, while methyl derivatives clearly dominate the field of Ln–Al bimetallic Ziegler catalysis.[7] For scandium, N-donating ancillary ligands were shown to stabilize diethyl complexes such as [{ArNC-(tBu) CHC (tBu) NAr} ScEt2](Ar= C6H3iPr2-2, 6)[8] and [{N (SiMe2CH2PiPr2) 2} ScEt2],[9] while ethyl Grignard reagents were employed in salt metathesis protocols. The monoethyl complexes [(dadmb) YEt (thf) 2](dadmb= 2, 2’-bis-[(tert-butyldimethylsilyl) amido]-6, 6’-dimethylbiphenyl)[10] and [Lu (μ-Et)(μ-H){μ-Et2Si (C5H4)(C5Me4)} 2Lu][11] were obtained from the hydrido derivatives by ethylene insertion. Tetraethylaluminate (AlEt4) À groups seem to be rather stable when bonded to divalent rare-earth-metal cations, as shown for the homoleptic complexes [Ln (AlEt4) 2] n (Ln= Eu, Sm, Yb),[12] which readily form monomeric donor adducts, for example,[Ln (AlEt4) 2 (thf) 2](Ln= Yb, Sm).[13] LnIII tetraethylaluminate complexes are scarce, probably because they display reactivity behavior reminiscent of [LnEt (AlEt3)](“ethyl in disguise”), bearing close resemblance to the intrinsically unstable Group 4 congeners.[14] Only the heteroleptic metallocene complexes [(C5Me5) 2Sm (AlEt4)],[15][(C5Me5) 2Sm-(AlEt4)(thf)],[16] and rac-[{Me2Si-(2-Me-C9H5) 2} Y-(AlEt3Me)][17] and the lanthanum carboxylate [(2, 4, 6-iPrC6H2CO2AlEt3) 2La (AlEt4)][18] were analyzed by X-ray diffraction.Herein we present the solid-state structure of homoleptic lanthanum (III) tetraethylaluminate 1 and elaborate on its thermal decomposition in solution by β-H transfer and ethane formation, as detected by NMR spectroscopy. A previous attempt to X-ray crystallographically analyze [La (AlEt4) 3](1) produced only a connectivity structure [19] owing to the low quality of the crystals that resulted from an unoptimized reaction protocol and partial decomposition of 1. We have now reinvestigated the synthesis of 1, treating [La (NMe2) 3-(LiCl) 3] instead of [La {N (SiHMe2) 2} 3 (thf) 2] with excess AlEt3, which enabled facile separation of byproduct [(Et2AlNMe2) 2] thus allowing isolation of pure material in good yield. Highly twinned crystals of complex 1 with a featherlike morphology could be harvested from hexane at À408C. Under the same conditions, these crystals transformed into ordered clear blocks in the course of …
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影响因子：
4.3
作者：
Gerber, Laura C. H.;Le Roux, Erwan;Anwander, Reiner
通讯作者：
Anwander, Reiner
与铁（0）形成立体特异性环酮：配体间反应的解剖
DOI：
--
发表时间：
1976
期刊：
影响因子：
--
作者：
E. Weissberger;P. Laszlo
通讯作者：
P. Laszlo
稳定的均配金属烷基
影响因子：
18.3
作者：
P. Davidson;M. Lappert;R. Pearce
通讯作者：
R. Pearce
[LnIIAlIII2(烷基)8]x：供体加成而不是供体诱导裂解。
影响因子：
4.9
作者：
M. G. Schrems;H. Dietrich;K. Törnroos;R. Anwander
通讯作者：
R. Anwander
影响因子：
2.8
作者：
BUSCH, MA;HARLOW, R;WATSON, PL
通讯作者：
WATSON, PL