Bis(4‐benzhydryl‐benzoxazol‐2‐yl)methane – from a Bulky NacNac Alternative to a Trianion in Alkali Metal Complexes

Abstract

A novel sterically demanding bis(4‐benzhydryl‐benzoxazol‐2‐yl)methane ligand 6 (4−BzhH2BoxCH2) was gained in a straightforward six‐step synthesis. Starting from this ligand monomeric [M(4‐BzhH2BoxCH)] (M=Na (7), K (81)) and dimeric [{M(4‐BzhH2BoxCH)}2] (M=K (82), Rb (9), Cs (10)) alkali metal complexes were synthesised by deprotonation. Abstraction of the potassium ion of 8 by reaction with 18‐crown‐6 resulted in the solvent separated ion pair [{(THF)2K@(18‐crown‐6)}{bis(4‐benzhydryl‐benzoxazol‐2‐yl)methanide}] (11), including the energetically favoured monoanionic (E,E)‐(4‐BzhH2BoxCH) ligand. Further reaction of 4−BzhH2BoxCH2 with three equivalents KH and two equivalents 18‐crown‐6 yielded polymeric [{(THF)2K@(18‐crown‐6)}{K@(18‐crown‐6)K(4‐BzhBoxCH)}]n (n→∞) (12) containing a trianionic ligand. The neutral ligand and herein reported alkali complexes were characterised by single X‐ray analyses identifying the latter as a promising precursor for low‐valent main group complexes.

Group 13 Heavier Carbene Analogues Stabilized by the Bulky Bis(4-benzhydryl-benzoxazol-2-yl)methanide Ligand

“…The bis­(4-benzhydryl-benzoxazol-2-yl)­methane ( 4‑BzhH2 Box 2 CH 2 ) is straightforwardly deprotonated at the methylene bridge by neat alkali metals or bases to bis­(4-benzhydryl-benzoxazol-2-yl)­methanide complexes [M 1 ( 4‑BzhH2 Box 2 CH)] [M 1 = Na ( I ), K ( II ), Rb, or Cs] . These alkali metal complexes (Scheme ), and in particular I and II , are ideal precursors for salt metathesis reactions.…”

“…Starting materials were purchased commercially and used without further purification. Bis­(4-benzhydrylbenzoxazol-2-yl)­methane ( 4‑BzhH2 Box 2 CH 2 ), “GaI” ([Ga] 2 [Ga 2 I 6 ]), , InOTf, and [{( Mes NacNac)­Mg} 2 ] , were synthesized according to literature procedures. 1 H, 19 F, and 13 C NMR as well as 1 H– 13 C HSQC and 1 H– 13 C HMBC spectroscopic data were recorded on a Bruker Ascend 400 MHz spectrometer and a Bruker Avance 300 MHz spectrometer and referenced to deuterated solvents (benzene- d 6 , bromobenzene- d 5 , thf- d 8 , and toluene- d 8 ) .…”

“…Moreover, reduction attempts of aluminum precursor complexes [AlRI­( 4‑Me Box 2 CH)] (R = Me or Et) or [AlX 2 (Box 2 CH)] (X = Cl or I) (Chart ) led to indefinable product mixtures. To enhance the steric shielding to facilitate the formation of a monomeric carbene-like metallacycle, we designed the bis­(4-benzhydryl-benzoxazyl-2-yl)­methane ( 4‑BzhH2 Box 2 CH 2 ) ligand …”

A Sodium Sodate as Precursor for Lanthanide Bis(4-R-benzoxazol-2-yl)methanide Single-Molecule Magnets

“…Previously reported dinuclear compounds commonly feature chloride-, oxygen-, nitrogen-, and sulfur-based bridges as well as radical or arene bridges. − The air-stable and easy tunable ligand family of bis­(4- R -benzoxa-2-yl)­methanides (so-called “box ligand” hereafter) represents an ideal model system to obtain lanthanide bridged systems, either through the ligand itself or via halide bridges. This ligand mimics the promising properties of the β-diketiminate ( nacnac ) scaffold with the five-membered metallacycle and an additional oxygen donor site for different coordination motifs. , The effect of diverse substituents has been deeply studied in main group chemistry for R = -H, -methyl, - i -propyl, - t -butyl, and -benzhydryl …”

Structural and Magnetic Studies on Lanthanide Bis(benzoxazol‐2‐yl)methanides

“…[5] Further substitution along the aromatic C 6 perimeter allows steric tailoring the coordination pocket. The influence of different substituents has been deeply explored for A, [3a] B, [6] C, [4] D [7] and E [8] in main group chemistry, as depicted in Scheme 1.…”