An η3‐Bound Allyl Ligand on Magnesium in a Mechanochemically Generated Mg/K Allyl Complex. Issue 24 (1st April 2020)

• Record Type: Journal Article
• Authors: Koby, Ross F.; Doerr, Alicia M.; Rightmire, Nicholas R.; Schley, Nathan D.; Long, Brian K.; Hanusa, Timothy P.
• Is Part Of: Angewandte Chemie international edition. Volume 59:Issue 24(2020)
• Page Start: 9542
• Page End: 9548
• Publication Date: 2020-04-01
• Subjects: allyl -- magnesium -- mechanochemistry -- polymerization -- potassium; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201916410
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Milling two equivalents of K[1, 3‐(SiMe3 )2 C3 H3 ] (=K[A′]) with MgX2 (X=Cl, Br) produces the allyl complex [K2 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 ]. Abstract : Pi at last ! Milling K[1, 3‐(SiMe3 )2 C3 H3 ] (=K[A′]) with MgX2 (X=Cl, Br) produces the orange heterometallic allyl complex [K2 MgA′4 ]. The crystal structure contains the first terminal η 3 ‐bound allyl ligand on a Mg center. Methyl methacrylate is polymerized by this complex, with activities that are comparable to K[A′] and greater than that of [{MgA′2 }2 ].