Introducing NacNac-Like Bis(4,6-isopropylbenzoxazol-2-yl)methanide in s-Block Metal Coordination

Abstract

Within this work, the field of bulky methanides in metal coordination is exceeded by the synthesis of the versatile and promising bis(4,6-isopropylbenzoxazol-2-yl)methane (7) ligand platform. As an enhancement in this class of ligands, isopropyl (iPr) substituents as steric-demanding groups have been successfully introduced in proximity to the coordination pocket, mimicking the shielding abilities of the ubiquitous NacNac ligand scaffold to improve the steric protection of a coordinated s-block metal cation. A percent buried volume (% V) calculation as well as an electronic structure analysis shades light onto the shielding and electronic abilities of the ligand in comparison to other selected methanides and diketiminates. Upon deprotonation with a variety of different group 1 and 2 metalation agents, a row of novel s-block metal complexes of the parent deprotonated monoanionic ligand 7 was obtained and structurally, as well as spectroscopically, characterized. In particular, in this context, the alkali-metal precursor complexes [Li(THF){(4,6-iPr-NCOCH)CH}] (8) and [K{μ-(4,6-iPr-NCOCH)CH}] (9) as well as the alkaline-earth-metal compounds [MgCl(THF){(4,6-iPr-NCOCH)CH}] (10) and [M(THF){(4,6-iPr-NCOCH)CH}] [M = Mg, n = 0 (11); M = Ca, n = 1 (12); M = Sr, n = 1 (13); M = Ba, n = 1 (14)] were successfully synthesized. Especially, the latter four exhibit interesting trends in the solid state as well as in solution within the metal series.

Radical Relatives: Facile Oxidation of Hetero-Diarylmethene Anions to Neutral Radicals

“…[25][26][27] Due to their relevance to porphyrins and the fluorescent properties of BODIPY dyes and related complexes, 28 dipyrrins have been extensively studied and shown to exhibit redox activity in their complexes and dipyrrin-fullerene triads. [29][30][31][32][33][34][35] Similarly to these studies, we have shown that a simply prepared anionic, imine-expanded dipyrrin acts as a ligand for iron and uranium complexes, 36 the latter showing ligand redox activity. 37 Due to the ligand-based LUMO, the sequential outer-sphere, one-electron reduction of the uranyl(VI) center to U(V) and U(IV) occurs by initial ligand reduction followed by electron-transfer to the metal.…”

Bis(benzoxazol‐2‐yl)methanes Hounding NacNac: Varieties and Applications in Main Group Metal Coordination

“…To better mimic and finally complement the shielding abilities of the famous NacNac ligand scaffold, steric demanding substituents were introduced at the 4‐position adjacent to the coordination pocket. Starting with methyl groups in bis(4‐Me‐benzoxazol‐2‐yl)methane ( C ), the steric bulk was successively increased by the introduction of isopropyl‐ ( D ) and tert ‐butyl ( E ) residues in the corresponding bis(4,6‐R‐benzoxazol‐2‐yl) (R = i Pr, t Bu) derivatives.…”

“…After preparation of the corresponding 3,5‐substituted 2‐aminophenol derivatives starting from 3,5‐isopropyl‐ or 3,5‐ tert ‐butylphenol, ligand platforms D and E are accessed according to procedure ( c ) depicted in Scheme . As a highlight, treatment of D and E with a magnesium chloride Hauser‐base gives the corresponding D ‐supported magnesium(II) chloride complexes (Scheme ) , …”

“…As a highlight, treatment of D and E with a magnesium chloride Hauser-base gives the corre-sponding D-supported magnesium(II) chloride complexes (Scheme 8). [23,24] Scheme 8. Preparation of magnesium chloride complexes based on the bis(4,6-R-benzoxazol-2-yl)methanes D (R = iPr) and E (R = tBu).…”

“…Furthermore, the electronic structure as well as donating properties of ligand platforms D and E were evaluated by electronic structure analyses. [23] The D-and E-based lithium complexes [Li(THF) 2 {(4,6-iPr-NCOC 6 H 2 ) 2 CH}] and [Li(THF)-{(4,6-tBu-NCOC 6 H 2 ) 2 CH}] were considered in comparison to the NacNac-supported structures [Li(THF){ tBu NacNac}], [43] [Li(THF)-{ Dipp NacNac}] [44] and amide-functionalized [Li(Et 2 O){N-Dipp -NacNac}] [45] (Figure 3, vide infra). Following trends could be derived from the computational results (NBO, NPA and NRT): • Only minor differences are observed between the considered structures.…”