An η³‐Bound Allyl Ligand on Magnesium in a Mechanochemically Generated Mg/K Allyl Complex

Abstract

Milling two equivalents of K[1,3‐(SiMe3)2C3H3] (=K[A′]) with MgX2 (X=Cl, Br) produces the allyl complex [K2MgA′4] (1). Crystals grown from toluene are of the solvated species [((η6‐tol)K)2MgA′4] ([1⋅2(tol)]), a trimetallic monomer with both bridging and terminal (η1) allyl ligands. When recrystallized from hexanes, the unsolvated 1 forms a 2D coordination polymer, in which the Mg is surrounded by three allyl ligands. The C−C bond lengths differ by only 0.028 Å, indicating virtually complete electron delocalization. This is an unprecedented coordination mode for an allyl ligand bound to Mg. DFT calculations indicate that in isolation, an η3‐allyl configuration on Mg is energetically preferred over the η1‐ (σ‐bonded) arrangement, but the Mg must be in a low coordination environment for it to be experimentally realized. Methyl methacrylate is effectively polymerized by 1, with activities that are comparable to K[A′] and greater than the homometallic magnesium complex [{MgA′2}2].

In Situ Grignard Metalation Method for the Synthesis of Hauser Bases

“…Mechanochemistry had been advanced to prepare air‐ and moisture‐sensitive alkaline‐earth metal compounds by ball milling [43] . Highly reactive organometallic potassium beryllates [44] and magnesates [45] were prepared with moderate yields as proof of concept for mechanochemical organometallic chemistry. Even though the preparation succeeded solvent‐free, the product had to be extracted with an anhydrous organic solvent.…”

Mechanochemical Rearrangements

“…Within this context, mechanochemistry has been shown to successfully enable rearrangement-type reactions in the area of main group chemistry. ,− We will present a couple of examples, which are not only somewhat relevant to the scope of this review but also produced molecular arrangements that are not accessible using conventions solution-based methods.…”