Silicon‐Bridged Bi‐ and Tridentate Lewis Acidic Host Systems

Abstract

Connecting multiple organic spacer functions via silicon core units leads to various organosilanes that are excellently suited as backbones for poly-Lewis acids (PLAs). Using ethynyl spacer groups, rigid bis-and tris-dioxabenzoborole (BCat)-substituted PLAs were prepared. The fixed orientation of the Lewis acidic functions of the PLAs is reflected in their solid-state structures. Further flexible PLAs were obtained by hydroboration of vinylsilanes using 9-borabicyclo[3.3.1]nonane (9-BBN), which shows the flexibility of the backbone motif. Host-guest experiments of the bidentate representatives with pyridine demonstrate the ability of both PLA-types (BCat or 9-BBN) for complexing neutral guest molecules. The rigid host system shows additionally a 1 : 1 adduct formation using a bridged diamine as guest compound.

Tridentate Lewis Acids Based on Tribenzotriquinacene Chalices

“…The coupling constants of 3 J H,H =17 Hz and 3 J H,H =18.0 Hz also indicated a trans ‐arrangement of the hydrogen atoms. An 11 B NMR chemical shift of 75.6 ppm as well as the broadening of the 13 C{ 1 H} NMR signal of the carbon atom adjacent to the boron atom are in agreement with the corresponding data for related compounds [7c,d,29] . We also noticed a too low carbon value in the elemental analysis of compounds 6 and 7 , as discussed above.…”

“…The 1 H NMR spectrum shows a singlet for the SiMe 3 groups of the bis(bis(trimethylsilyl)methyl) substituents (Bis) with a chemical shift of 0.31 ppm and a singlet for the methine hydrogen atoms (Al−CH) with a chemical shift of −0.43 ppm, indicating tri‐coordination at the aluminium atom [11,26] . In the elemental analysis of compounds 3 and 5 , we noticed that the carbon values were too low, which may be due to the formation of the corresponding metal carbides, as has been observed in previous work on similar compounds [7d,11a] . Even the addition of vanadium pentoxide did not improve the carbon values.…”

A guide to secondary coordination sphere editing

“…This area has benefited from steady contributions from the main group community that provide routes of access. [76][77][78][79][80] Poly Lewis acid-containing compounds such as these are often prepared using hydroboration (addition of a B-H bond across a point of unsaturation). 81 In most of these case studies, hydroboration was performed post metal Scheme 31 Ba 2+ uptake causes enhanced activity for CO 2 -to-CO reduction.…”

The Field of Main Group Lewis Acids and Lewis Superacids: Important Basics and Recent Developments

“…[199] 38 Another approach to bi-and tridentate boron-containing LA is based on silicon-containing compounds as bridges between functional boron-containing LA groups. [123] Complexes of 39 with two pyridine molecules and with N,N,N',N'-tetramethylpropanediamine (tmpda) were obtained, for the latter case a cyclic 1 : 1 complex was assumed. Structure of 40 • 2Py was established by X-ray structural analysis (BÀ N distances 1.654 Å, B … B distance 6.682(4) Å).…”

“…Structure of 40 • 2Py was established by X-ray structural analysis (BÀ N distances 1.654 Å, B … B distance 6.682(4) Å). [123] Tetradentate LA (43) based on syn-photodimer of diethynylantracene (Scheme 20) was synthesized by Mitzel and coauthors in 2021. [124] It forms complexes 43 • 4Py, 43 • 4NH 3 , 43 • 4 N 2 H 4 (from benzene) and 43 • 5 N 2 H 4 (from CH 2 Cl 2 ) which were structurally characterized in the solid state.…”