Lewis acidic alkaline earth metal complexes with a perfluorinated diphenylamide ligand

Alkaline earth metal (Ae) chemistry with the anion [N(C6F5)(2)](-) has been explored. Deprotonation of the amine (C6F5)(2)NH, abbreviated in here as (NH)-H-F, with 0.5 equivalent of AeN(2) (N = N(SiMe3)(2)) is fast and gave, dependent on the solvent, the complexes AeN(2)(F), AeN(2)(F)(THF)(2) and AeN(2)(F)(Et2O)(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(2)(F)(THF)(2) (Ae = Mg, Ca, Sr) and AeN(2)(F)(Et2O)(2) (Ae = Mg, Ca) are presented and compared with those of AeN(2)(THF)(2). In addition, crystal structures of the homoleptic dimer (MgN2F)(2) and the heteroleptic dimers (N(F)AeN)(2) (Ae = Mg, Ca, Sr) are discussed. All structures are strongly influenced by very short AeF contacts down to circa 2.11 angstrom (Mg), 2.50 angstrom (Ca) and 2.73 angstrom (Sr). AIM analysis illustrates that, although AeF contacts are short, there is no bond-critical-point along this axis, indicating an essentially electrostatic interaction. The monomeric complexes feature strong C6F5C6F5 -stacking, resulting in unusually acute N-F-Ae-N-F angles as small as 95 degrees. Heteroleptic (N(F)AeN)(2) complexes retain their dimeric structure in C6D6 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 MgN2F 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 MgN2F and CaN2F is comparable to that of B(C6F5)(3). Dimeric (MgN2F)(2) fully abstracts Et3PO from Et3POB(C6F5)(3) and may have potential in Lewis acid catalysis.