1,4-Dioxane Adducts of Grignard Reagents: Synthesis, Ether Fragmentation Reactions, and Structural Diversity of Grignard Reagent/1,4-Dioxane Complexes

The 1,4-dioxane precipitation method was employed to obtain solutions of R2Mg from Grignard reagents via precipitation of polymeric magnesium dihalides as dioxane adducts. The addition of a slight excess of dioxane resulted in partial cleavage of the initially formed [(μ-diox)MgR2]∞ polymer into smaller fragments of the type [(diox)n+1(MgR2)n]. In addition to the polymeric compounds [(μ-diox)MgR2]∞, as found for [(μ-diox-O,O’)Mg(cyclo-C6H11)2]∞ (1), other oligomers such as [(diox)3(Mg{CH2Ph}2)2] (2) can be obtained from such solutions. In the system MesMgBr/1,4-dioxane the compounds [(μ-diox)MgBr2]∞ and [(μ-diox)Mg(Mes)2]∞ are both sparingly soluble, offering the opportunity to remove most of these compounds from the reaction mixture and leaving the products of ether cleavage reactions as the major species in solution. Using this procedure, the new ether degradation products [(diox)Mg(Mes)(μ-OEt)]2 (3) and [(EtOCH(Me)CH(Me)OEt)Mg(Mes)2] (4) were isolated. Excess dioxane yields mononuclear [(diox)2Mg(Mes)2] (5). Exchange of the thf coligands in closely related [(thf)2Mg(Mes)2] for other Lewis bases such as 2,2′-bipyridine (bpy) and 2,4,6-trimethylphenyl (Mes) anions allowed the preparation of [(bpy)Mg(Mes)2] (6) and [(thf)4Li]+[Mg(Mes)3]− (7). Molecular structures of all new compounds 2−7 are reported.

采用1,4-二氧六环沉淀法，通过聚合二卤化镁作为二氧六环加成物的方式，从格氏试剂中获得了R2Mg的溶液。微过量的二氧六环的加入，导致最初形成的[(μ-diox)MgR2]∞聚合物部分裂解，形成了诸如[(diox)n+1(MgR2)n]类型的小片段。除了聚合化合物[(μ-diox)MgR2]∞（如[(μ-diox-O,O’)Mg(cyclo-C6H11)2]∞（1）中所示），还可以从此类溶液中获得其他低聚物，如[(diox)3(Mg{CH2Ph}2)2]（2）。在MesMgBr/1,4-二氧六环体系中，化合物[(μ-diox)MgBr2]∞和[(μ-diox)Mg(Mes)2]∞均难溶于水，这为从反应混合物中移除大部分此类化合物提供了机会，使得醚裂解反应的产物成为溶液中的主要物种。采用该方法，新得的醚降解产物[(diox)Mg(Mes)(μ-OEt)]2（3）和[(EtOCH(Me)CH(Me)OEt)Mg(Mes)2]（4）得以分离。过量的二氧六环生成了单核的[(diox)2Mg(Mes)2]（5）。将密切相关[(thf)2Mg(Mes)2]中的thf配体与其他路易斯碱如2,2′-联吡啶（bpy）和2,4,6-三甲基苯（Mes）阴离子交换，允许制备[(bpy)Mg(Mes)2]（6）和[(thf)4Li]+[Mg(Mes)3]−（7）。所有新化合物2−7的分子结构已报道。