Synthesis and Structures of Monomeric Magnesium, Calcium, Strontium, and Barium Amides Involving the N,N-(2,4,6-Trimethylphenyl)(trimethylsilyl)amido Ligand

Abstract

An extended family of aryl-substituted alkaline earth metal silylamides M{N(2,4,6-Me3C6H2)(SiMe3)}donor(n) was prepared using alkane elimination (Mg), salt elimination (Ca, Sr, Ba), and direct metalation (Sr, Ba). Three different donors, THF, TMEDA (TMEDA = N,N,N',N'-tetramethylethylenediamine), and PMDTA (PMDTA = N,N,N',N'',N''-pentamethyldiethylenetriamine) were employed to study their influence on the coordination chemistry of the target compounds, producing monomeric species with the composition M{N(2,4,6-Me3C6H2)(SiMe3)}2(THF)2 (M = Mg, Ca, Sr, Ba), M{N(2,4,6-Me3C6H2)(SiMe3)}2TMEDA (M = Ca, Ba), and M{N(2,4,6-Me3C6H2)(SiMe3)}2PMDTA (M = Sr, Ba). For the heavier metal analogues, varying degrees of agostic interactions are completing the coordination sphere of the metals. Compounds were characterized using IR and NMR spectroscopy in addition to X-ray crystallography.

Advances in alkaline earth-nitrogen chemistry

“…However, less is known about the role that agostic interactions of the type M· · ·H-C play in stabilizing these metal centers. Agostic interactions are described as weak interactions of a coordinatively unsaturated metal with a C-H bond [17][18][19]. Although present in a large number of alkaline earth compounds, agostic interactions are rarely reported and frequently ignored, despite their prevalence and growing importance in the steric and electronic stabilization of large, highly reactive metal centers [18,19].…”

“…Further complicating the identification of these weak interactions is that formal cut-off values have not been well established. All agostic interactions reported herein are within range of the sum of van der Waals radii ( (r wAe + r wH )) for a metal-hydrogen bond, and are summarized in Table 2 [4], along with cut-off values established from published work [18,19].…”

Surface Organobarium and Organomagnesium Chemistry on Periodic Mesoporous Silica MCM‐41: Convergent and Sequential Approaches Traced by Molecular Models

“…Reliable elemental analyses were difficult to obtain for several complexes (especially for barium silylamides); a wellknown problem in alkaline earth metal chemistry. [28,44] Metal analyses were obtained from Mikroanalytisches Labor Pascher (Remagen-Bandorf; Germany). IR spectra were recorded on a Thermo Scientific Nicolet6700 FTIR spectrometer by using Nujol mulls sandwiched between CsI plates or a DRIFT cell equipped with KBr windows, for which the samples were mixed with KBr powder (80 % in weight).…”

Diene Dissolution of the Heavier Alkaline Earth Metals

“…This is a well-known problem in alkaline earth metal chemistry. [21] IR spectra were recorded on a Thermo Scientific Nicolet 6700 FTIR spectrometer using a DRIFT cell equipped with KBr windows, for which the samples were mixed with KBr powder (80 % in weight), or on a JascoFT/IR-230 spectrometer using Nujol mulls sandwiched between NaCl plates. The spectra were recorded in 256 scans (DRIFT) or 32 scans (NaCl plates) at ambient temperature in the range of 4000 to 400 cm -1 with a spectral resolution of 2 cm -1 .…”