Lewis Acidic Cationic Strontium and Barium Complexes

Lewis acidic (BDI)Ae + cations of the heavier metals Sr and Ba, which are not stabilized by polar solvents, have been obtained by double deprotonation of (BDI)H 2 + with either SrN’’ 2 or BaN’’ 2 ; BDI = HC[C(Me)N(DIPP)] 2 , DIPP = 2,6‐di iso propylphenyl, Ae = alkaline earth, N’’ = N(SiMe 3 ) 2 . Due to clathrate formation [(BDI)Ae + ][B(C 6 F 5 ) 4 − ] could not be crystallized, but pyrene addition gave crystalline [(BDI)Ae +  ⋅ pyrene][B(C 6 F 5 ) 4 − ] which was structurally characterized for Ae = Mg, Ca, Sr, Ba. (R 2 N)Ae + cations of the heavier metals Sr and Ba were obtained by reaction of Ae(NR 2 ) 2 with [Ph 3 C + ][B(C 6 F 5 ) 4 − ] or [PhNMe 2 H + ][B(C 6 F 5 ) 4 − ]. Following complexes were structurally characterized: [N’’Ba +  ⋅ (tol) 2 ][B(C 6 F 5 ) 4 − ], [N*Sr +  ⋅ PhNMe 2 ][B(C 6 F 5 ) 4 − ], [N*Ba +  ⋅ tol][B(C 6 F 5 ) 4 − ] and [N*Ba +  ⋅ C 6 H 6 ][B(C 6 F 5 ) 4 − ]; tol = toluene and N* = N(Si i Pr 3 ) 2 . DFT calculations show that Sr⋅⋅⋅PhNMe 2 coordination is preferred over Sr⋅⋅⋅toluene bonding. The (R 2 N)Ae + cations can be used as Brønsted bases (reaction with (BDI)H gave (BDI)Ae + ) and may be useful precursors for a variety of Lewis base‐free RAe + cations. DFT calculations, limited to monomeric model systems including B(C 6 F 5 ) 4 − (ωB97XD/def2tzvpp//ωB97XD/def2svp), show that there is negligible electron transfer from the pyrene or toluene ligands to the Ae 2+ cation. Electrostatic attraction originates from charge‐induced polarization of the π ‐electron density in the toluene and pyrene ligands.