The dimeric β-diketiminato calcium hydride, [(BDI)CaH]₂ (BDI = HC{(Me)CN-2,6-iPr₂C₆H₃}₂), reacts with ZnMe₂ to afford the bimetallic calcium zincate complex, [(BDI)Ca(μ-CH₃)₂Zn(μ-H)]₂, which subsequently undergoes an intramolecular reaction to effect the formation of [(BDI)CaMe]₂, a notable omission from the homologous series of β-diketiminato alkylcalcium derivatives. Since the discovery of Grignard reagents in 1900,1 organomagnesium derivatives have prevailed as some of the most widely employed compounds in chemical synthesis. In contrast, exploration of magnesium’s heavier congener, calcium, lay largely dormant throughout the 20th Century, to the extent that it has even been deemed as the “sleeping beauty” of organometallic chemistry.2 Despite reports of σ-C-Ca-bonded calcium alkyl and aryl complexes from as early as 1905,3,4 the first crystallographically verified calcium σ-alkyl, [Ca{CH(SiMe3)2}2(Diox)2] (Diox = 1,4-dioxane), was only reported by Cloke and Lappert in 1991.5 Like this species, many subsequently characterised diorganocalcium compounds were dependent on the use of silylated and kinetically stabilising organic anions.6 More recently, however, a defined and characteristic chemistry has finally started to emerge for derivatives of wholly hydrocarbon ligands.2 Especially notable in this regard are routes to a variety of di- and monoaryl calcium reagents and dimethylcalcium devised, respectively, by the groups of Westerhausen and Anwander.7,8 While sufficiently remarkable to merit a mononymic account of its synthesis,8 the subsequent reactivity of [CaMe2]∞ in the absence of secondary donors is relatively limited as a consequence of its polymeric nature and consequent poor solubility in non-coordinating media.8 Further advancements have, thus, focused on heteroleptic derivatives,9 with the β-diketiminate ligand scaffold proving a particularly adept, hydrocarbon-soluble spectator anion.10 While σ-n-alkyl species had previously proved inaccessible via the analogous THF-adducted hydride, [(BDI)Ca(THF)H]2 (BDI = HC{(Me)CN-2,6-iPr2C6H3}2),11 its base-free variant, [(BDI)CaH]2 (1),12 was found to be reactive toward terminal alkenes to provide a wide range of dimeric σ-n-alkyl derivatives, [(BDI)Ca(R)]2 (Scheme 1).13 While a further impact of reduction in coordinative saturation at the calcium centre was manifest in the ability of such σ-alkyls to effect the nucleophilic alkylation of benzene (Scheme 1),12 a similar alkene insertion-based approach is clearly inapplicable to the synthesis of the simplest methylcalcium homologue.

中文翻译：

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分子甲基钙的途径


二聚体β-二酮亚胺氢化钙，[(BDI)CaH] ₂ (BDI = HC{(Me)CN-2,6-iPr ₂ C ₆ H ₃ } ₂ )，与 ZnMe ₂ 反应生成双金属锌酸钙络合物，[(BDI)Ca(μ-CH ₃ Zn(μ-H)] ₂ ，随后发生分子内反应，形成 [(BDI)CaMe] ₂ ，β-二酮亚胺烷基钙衍生物同系系列中的一个显着遗漏。自 1900 年发现格氏试剂1以来，有机镁衍生物已成为化学合成中应用最广泛的化合物之一。相比之下，对镁的较重同系物钙的探索在整个 20 世纪基本上处于休眠状态，甚至被视为有机金属化学的“睡美人”。2 尽管有关于 σ-C-Ca 键合钙的报道早在 1905 年，3,4 就首次报道了烷基和芳基复合物，第一个经过晶体学验证的 σ-烷基钙，[Ca{CH(SiMe3)2}2(Diox)2]（Diox = 1,4-二恶烷）由 Cloke 和 Lappert 于 1991 年提出。5 像这个物种一样，许多随后表征的二有机钙化合物依赖于硅烷化和动力学稳定有机阴离子的使用。 6 然而，最近，对于全烃配体的衍生物，终于开始出现明确的特征化学.2 在这方面特别值得注意的是 Westerhausen 和 Anwander 小组分别设计的各种二芳基钙试剂和单芳基钙试剂以及二甲基钙的路线。7,8 虽然其合成足够显着，值得对其合成进行单名解释，8 由于其聚合性质以及随后在非配位介质中的溶解性差，在没有二次供体的情况下，[CaMe2]∞ 的后续反应性相对有限。 8 因此，进一步的进展集中在杂配衍生物上，9 β-二酮亚胺配体支架被证明是一种特别适合的、碳氢化合物可溶的旁观阴离子。 10 虽然 σ-n-烷基物种之前已被证明无法通过类似的 THF 加合氢化物获得, [(BDI)Ca(THF)H]2 (BDI = HC{(Me)CN-2,6-iPr2C6H3}2),11 其无碱变体，[(BDI)CaH]2 (1),12被发现对末端烯烃具有反应性，可提供多种二聚 σ-n-烷基衍生物，[(BDI)Ca(R)]2（方案 1）。13 而钙配位饱和度降低的进一步影响中心表现在此类 σ-烷基影响苯亲核烷基化的能力（方案 1），12 类似的基于烯烃插入的方法显然不适用于最简单的甲基钙同系物的合成。