A Rare-Earth-Metal Ensemble of the Tebbe Reagent: Scope of Coligands and Carbonyl Olefination
A Rare-Earth-Metal Ensemble of the Tebbe Reagent: Scope of Coligands and Carbonyl Olefination
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DOI：
10.1021/acs.organomet.0c00447
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发表时间：
2020-10-12
期刊：
影响因子：
2.8
通讯作者：
Anwander, Reiner
中科院分区：
文献类型：
--
作者：
Birkelbach, Verena M.;Kracht, Felix;Anwander, Reiner
用温和的卤代转移试剂SiMe3X(X=Cl，Br，I)处理半夹心配合物Cp(R)Ln-(AlMe4)(2)(Cp-R=C5Me5，C5Me4SiMe3；Ln=Y，La，Lu)，得到了高效和选择性的卤代/四甲基铝交换。根据稀土金属的大小，可以得到二聚体[Cp(R)Ln(AlMe4)(Mu-X)](2)(Ln=Y，Lu)和十金属[(Cp3La3)-La-R(AlMe4)(2)(Mu-X)(4)](2)。施主(四氢呋喃)诱导的四甲基铝裂解使Y(X=Cl，Br)和La(X=Cl，Br，I)以较高的产率合成了“无甲基”的亚甲基/卤代混合络合物Cp(3)(R)Ln(3)(mu-X)(3)(mu(3)-X)(mu(3)-CH2)(THF)(3)。此外，通过甲基/卤代交换，(C5Me5)(3)Y-3(mu-Me)(3)(mu(3)-Me)(mu(3)-CH2)(THF)(2)和SiMe3X通过四甲基硅烷消除，可以得到亚甲基/卤代Y(III)混合配合物。所有的亚甲基化合物在烯化反应中都被发现是有效的Schroc型亲核卡宾，将酮和醛转化为各自的末端烯烃。这种反应性与主要的Tebbe试剂一样高，但对要求严格的官能化底物(如酯)的耐受性较差。与特贝试剂不同，络合物CpR(3)Ln(3)(mu-X)(3)(mu(3)-X)(mu(3)-CH2)(THF)(3)以高效的方式聚合三角洲戊内酯，生成分子量分布M-w/M-n低至1.13的聚内酯。此外，还描述了Tebbe试剂的溴代变体Cp2Ti(Mu-CH2)(Mu-BrAlMe2)，具有类似的合成限制：即三价物种Cp2Ti(Mu-Br2)(2)AlMe2的共生(从而共结晶)。
Treatment of the half-sandwich complexes Cp(R)Ln-(AlMe4)(2) (Cp-R = C5Me5, C5Me4SiMe3; Ln = Y, La, Lu) with the mild halogenido transfer reagents SiMe3X (X = Cl, Br, I) resulted in efficient and selective halogenido/tetramethylaluminato exchange. Depending on the size of the rare-earth metal, dimeric [Cp(R)Ln(AlMe4)(mu-X)](2) (Ln = Y, Lu) and decametallic [(Cp3La3)-La-R(AlMe4)(2)(mu-X)(4)](2) could be obtained. Donor (THF)-induced tetramethylaluminato cleavage gave access to "methyl-free" mixed methylidene/halogenido complexes Cp(3)(R)Ln(3)(mu-X)(3)(mu(3)-X)(mu(3)-CH2)(THF)(3) for yttrium (X = Cl, Br) and lanthanum (X = Cl, Br, I) in good yields. Additionally, mixed methylidene/halogenido Y(III) complexes could be obtained via methyl/halogenido exchange employing (C5Me5)(3)Y-3(mu-Me)(3)(mu(3)-Me)(mu(3)-CH2)(THF)(2) and SiMe3X via tetramethylsilane elimination. All methylidene complexes were probed in olefination reactions and found to act as efficient Schrock-type nucleophilic carbenes converting ketones and aldehydes into the respective terminal alkenes. Such reactivity is as high as that of the prominent Tebbe reagent but is less tolerant toward sterically demanding and functionalized substrates (such as esters). In contrast to the Tebbe reagent, complexes CpR(3)Ln(3)(mu-X)(3)(mu(3)-X)(mu(3)-CH2)(THF)(3) polymerize delta-valerolactone in an efficient manner, generating polylactones with molecular weight distributions M-w/M-n as low as 1.13. Moreover, the bromido variant of the Tebbe reagent, Cp2Ti(mu-CH2)(mu-Br)AlMe2, is described, underlying similar synthesis limitations: that is, the coformation (and hence cocrystallization) of the trivalent species Cp2Ti(mu-Br)(2)AlMe2.