Lewis acidic alkaline earth metal complexes with a perfluorinated diphenylamide ligand. Issue 20 (8th May 2019)

• Record Type: Journal Article
• Authors: Fischer, Christian A.; Rösch, Andreas; Elsen, Holger; Ballmann, Gerd; Wiesinger, Michael; Langer, Jens; Färber, Christian; Harder, Sjoerd
• Is Part Of: Dalton transactions. Volume 48:Issue 20(2019)
• Page Start: 6757
• Page End: 6766
• Publication Date: 2019-05-08
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c9dt01272a
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Alkaline earth metal chemistry with the anion [N(C6 F5 )2 ] − has been explored. Complexes are stabilized by metal⋯F interactions. Mg[N(C6 F5 )2 ]2 is a stronger Lewis acid than B(C6 F5 )3 . Abstract : Alkaline earth metal (Ae) chemistry with the anion [N(C6 F5 )2 ] − has been explored. Deprotonation of the amine (C6 F5 )2 NH, abbreviated in here as N F H, with 0.5 equivalent of AeN′′2 (N′′ = N(SiMe3 )2 ) is fast and gave, dependent on the solvent, the complexes AeN F 2, AeN F 2 ·(THF)2 and AeN F 2 ·(Et2 O)2 (Ae = Mg, Ca, Sr). Using a 1/1 ratio, mixed amide complexes were obtained: N F AeN′′ (Ae = Mg, Ca, Sr). Crystal structures of the monomers AeN F 2 ·(THF)2 (Ae = Mg, Ca, Sr) and AeN F 2 ·(Et2 O)2 (Ae = Mg, Ca) are presented and compared with those of AeN′′2 ·(THF)2 . In addition, crystal structures of the homoleptic dimer (MgN F 2 )2 and the heteroleptic dimers (N F AeN′′)2 (Ae = Mg, Ca, Sr) are discussed. All structures are strongly influenced by very short Ae⋯F contacts down to circa 2.11 Å (Mg), 2.50 Å (Ca) and 2.73 Å (Sr). AIM analysis illustrates that, although Ae⋯F contacts are short, there is no bond-critical-point along this axis, indicating an essentially electrostatic interaction. The monomeric complexes feature strong C6 F5 ⋯C6 F5 π-stacking, resulting in unusually acute N F –Ae–N F angles as small as 95°. Heteroleptic (N F AeN′′)2 complexes retain their dimeric structure in C6 D6 solution and there is no indication of ligand scrambling by the Schlenk equilibrium, suggesting that an electron withdrawing ligand may stabilize heteroleptic complexes. According to DFT calculations, the heteroleptic arrangement is 70 kJ mol −1 more stable than the homoleptic dimers. The Lewis acidity of MgN F 2 has been quantified with the Gutmann–Beckett method and by calculation of the Fluoride-Ion-Affinity. The latter calculations show that the Lewis acidity of MgN F 2 and CaN F 2 is comparable to that of B(C6 F5 )3 . Dimeric (MgN F 2 )2 fully abstracts Et3 PO from Et3 PO·B(C6 F5 )3 and may have potential in Lewis acid catalysis.