Lewis Acidic Cationic Strontium and Barium Complexes

Abstract

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-diisopropylphenyl, Ae = alkaline earth, N'' = N(SiMe 3 ) 2 . Due to clathrate formation [(BDI)Ae + ][B(C 6 F 5 ) 4 À ] could not be crystallized, but pyrene addition gave crystalline [(BDI)Ae + • pyrene][B(C 6 F 5 ) 4 À ] 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 À ] or [PhNMe 2 H + ] [B(C 6 F 5 ) 4 À ]. Following complexes were structurally characterized: [N''Ba + • (tol) 2 ][B(C 6 F 5 ) 4 À ], [N*Sr + • PhNMe 2 ][B(C 6 F 5 ) 4 À ], [N*Ba + • tol] [B(C 6 F 5 ) 4 À ] and [N*Ba + • C 6 H 6 ][B(C 6 F 5 ) 4 À ]; tol = toluene and N* = N(SiiPr 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 À(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 p-electron density in the toluene and pyrene ligands.

Enforcing Metal–Arene Interactions in Bulky p-Terphenyl Bis(anilide) Complexes of Group 2 Metals (Be–Ba): Potential Precursors for Low-Oxidation-State Alkaline Earth Metal Systems

“…Based on thermodynamic considerations, the intramolecular metal–π interactions in the homologous series 2 , 5 , 6 , 7 , including hypothetical 11 , were investigated by NBO and AIM analyses to understand the bonding situation. The charges on the metal centers obtained from NPA ( 11 + 1.77, 2 + 1.83, 5 + 1.78, 6 + 1.82, 7 + 1.84) and AIM analyses ( 11 + 1.70, 2 + 1.69, 5 + 1.56, 6 + 1.59, 7 + 1.58) (Table S2) show no clear trends in dependency of the nature of the metal, yet are consistent with those obtained for other systems containing alkaline earth metal−π interactions. − This shows that the N–M bonding and the M–π interactions are mainly of electrostatic nature and that there is negligible charge transfer from the ligand to the M 2+ metal cation. Consistently, no significant corresponding orbital interactions between the central arene π system and the metal were observed upon inspection of the filled bonding molecular orbitals.…”

On the existence of low-valent magnesium–calcium complexes

“…Although there is currently no proof that benzene lowers the aggregation number of VII and X (DOSY measurements were inconclusive), it is assumed that aromatic (co)solvents inuence dimer-monomer equilibria by coordination to the s-block metal. Strong interactions between Ae metal cations and p-systems have been reported [33][34][35][36][37] and are also supported by DFT calculations (Fig. S52 ‡).…”

A Barium Complex of the Silanide SiH3–: Hydride Surrogate and Source of Silicon

“…The Ba–N bond is Ba–N 2.561(3) Å, and the closest Ba–C contact is 3.113(4) Å, shorter than in 2 , reflecting the low number of ligands. It is noteworthy that the barium-arene contacts are shorter than in Harder’s [(Me 3 Si) 2 NBa­(toluene) 2 ] + or [(BDI)­Ba­(pyrene)] + cations (3.279(9) and 3.241(2) Å, BDI = β-diketiminate) …”

“…Among the attempts to finally achieve SiH 3 − transfer, the tetrylene-derived cations [( dtbp Cbz)E][Al(OC 4 F 9 ) 4 ] (E = Ge, Sn, Pb) appeared to be suitable starting materials. When [( dtbp Cbz)Ge][Al(OC 4 F 9 ) 4 ] and [( dtbp Cbz)Ba(SiH 3 )] were combined in fluorobenzene, the color of the reaction mixture remained orange-red, but NMR spectroscopy indicated the 54 The expected metathesis product [( dtbp Cbz)Ge(SiH 3 )] ( 6) was detected in the initial reaction mixture but is not stable in solution. It can be characterized by resonance at 2.79 ppm in the 1 H NMR spectrum, showing Si satellites with J HSi = 180 Hz and a corresponding 29 Si NMR resonance at −78.0 ppm, in agreement with DFT-predicted values (see Supporting Information, S4) as well as silyl germanes such as Ge(SiH 3 ) 4 (δ( 2 9 Si) −85.2 ppm) 5 5 , 5 6 or [{(Me 3 Si) 2 N}Ge{B-(NDippCH) 2 }H(SiH 3 )] (δ( 29 Si) 87.3 ppm).…”