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An η 3 ‐Bound Allyl Ligand on Magnesium in a Mechanochemically Generated Mg/K Allyl Complex
Author(s) -
Koby Ross F.,
Doerr Alicia M.,
Rightmire Nicholas R.,
Schley Nathan D.,
Long Brian K.,
Hanusa Timothy P.
Publication year - 2020
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201916410
Subject(s) - magnesium , chemistry , monomer , delocalized electron , ligand (biochemistry) , polymerization , toluene , crystallography , medicinal chemistry , stereochemistry , polymer , organic chemistry , biochemistry , receptor
Milling two equivalents of K[1,3‐(SiMe 3 ) 2 C 3 H 3 ] (=K[A′]) with MgX 2 (X=Cl, Br) produces the allyl complex [K 2 MgA′ 4 ] ( 1 ). Crystals grown from toluene are of the solvated species [((η 6 ‐tol)K) 2 MgA′ 4 ] ([ 1 ⋅2(tol)]), a trimetallic monomer with both bridging and terminal (η 1 ) 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 η 3 ‐allyl configuration on Mg is energetically preferred over the η 1 ‐ (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 ].