In situ Grignard Metalation Method, Part II: Scope of the One‐Pot Synthesis of Organocalcium Compounds

Krieck

et al. 2023

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Section: In Situ Generation Of Magnesium‐ and Calcium‐based Grignard ...mentioning

confidence: 81%

“…[118] In case of calcium, the equilibrium lies on the side of homoleptic calcocenes; heteroleptic cyclopentadienylcalcium bromides were only observed as intermediate species. [119] Enhancing the steric bulk of the substituents is disadvantageous.…”

Section: Scope Of the In Situ Grignard Metalation Methods (Igmm)mentioning

confidence: 99%

In Situ Generation of Magnesium‐ and Calcium‐Based Grignard Reagents for Amide Synthesis

Krieck

et al. 2023

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In situ Grignard Metalation Method, Part II: Scope of the One‐Pot Synthesis of Organocalcium Compounds

Koch

et al. 2022

The in situ Grignard Metalation Method (iGMM) is a straightforward one-pot strategy to synthesize alkaline-earth metal amides in multi-gram scale with high yields via addition of bromoethane to an ethereal suspension of a primary or secondary amine and magnesium (Part I) or calcium (Part II). This method is highly advantageous because no activation of calcium is required prior to the reaction. Contrary to the magnesium-based iGMM, there are some limitations, the most conspicuous one is the large influence of steric factors.The preparation of Ca(hmds) 2 succeeds smoothly within a few hours with excellent yields opening the opportunity to prepare large amounts of this reagent. Side reactions and transfer of the iGMM to substituted anilines and N-heterocycles as well as other H-acidic substrates such as cyclopentadienes are studied. Bulky amidines cannot be converted directly to calcium amidinates via the iGMM but stoichiometric calciation with Ca(hmds) 2 enables their preparation.

Synthesis of Sterically Encumbered Alkaline‐Earth Metal Amides Applying the In Situ Grignard Reagent Formation

Liebing

et al. 2023

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Magnesium and calcium are too inert to deprotonate amines directly. For the synthesis of bulky amides alternative strategies are required and in the past, N-bound trialkylsilyl groups have been used to ease metalation reactions. The in situ Grignard reagent formation in stirred suspensions of magnesium or calcium with hydryl halide and imine in THF allows the synthesis of a plethora of amides with bulky silyl-free substituents. Ball milling protocols partially favor competitive side reactions such as aza-pinacol coupling reactions. Calcium is the advantageous choice for the in situ Grignard reagent formation and subsequent addition onto the imines yielding bulky calcium bis(amides) whereas the stronger reducing heavier alkaline-earth metals strontium and barium are less selective and hence, the aza-pinacol coupling reaction becomes competitive. Exemplary, the solid-state molecular structures of [(Et 2 O)Mg(N(Ph)(CHPh 2 ) 2 ] and [(Et 2 O) 2 Ca(N(Ph)(CHPh 2 ) 2 ] have been determined.