Alkali metal complexes based on bisheterocyclomethanide ligands

Abstract

A series of new alkali metal complexes containing deprotonated bisheterocyclomethanide were synthesised and structurally as well as spectroscopically characterised. Starting from the neutral bis-(benzoxazol-2-yl)methane ({NCOC 6 H 4 } 2 CH 2 ), the complexes were obtained by facile deprotonation of the methylene bridge with nbutyllithium (nBuLi) or potassium hydride. Each of the resulting complexes(n → ∞) was analysed in the solid state by single crystal X-ray diffraction and in solution by various NMR techniques. All the compounds show a nearly planar ligand with the alkali metal ion chelated by the two ring nitrogen atoms of the conjugated C 3 N 2 moiety. Furthermore, water NMR titration experiments revealed that both compounds 2 and 3 are examples of water-stable reactive organo potassium compounds. Due to their hydrolysis stability, these complexes are under further investigations in deep eutectic solvents.

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

“…Crystals suitable for single XRD experiments were grown by vapour diffusion of pentane to a saturated THF solution of 11 at ambient temperature after 3 d. The colourless crystals in the triclinic space group P contain one bis(4‐benzhydryl‐benzoxazol‐2‐yl)methanide anion and two halve (THF) 2 K(18‐crown‐6)} cations in the asymmetric unit (Figure 5 ). In contrast to [( L )K(18‐crown‐6)] ( L = I − , III − )[ 16c , 16d , 38 ] that develop contact ion pairs in the solid, complex 11 was found to form a solvent separated ion pair. Expectedly, the ( Z , Z )‐( 4‐BzhH2 BoxCH) isomer seems to be preferred over the ( Z , E / E,Z )‐ or ( E , E )‐( 4‐BzhH2 BoxCH) isomers in the solid‐state.…”

“…Furthermore, potassium phenyl carbon distances suggest that the cation is η 2 ‐(K1−C30 3.467(2) Å, K1−C31 3.224(2) Å) and η 3 ‐coordinated (K1−C23 3.314(2) Å, K1−C27 3.503(2) Å, K1−C28 3.236(2) Å) by one phenyl residue of each benzhydryl group (A search in the CCDC version 5.41 (Aug. 2020) [30] for structures with K and phenyl groups excluding η 6 ‐coordinated ones provided a range of short contacts between K and C ortho of 2.77 to 3.76 Å). [ 29c , 30 ] In addition, a toluene molecule is capping the cation in a η 3 ‐fashion (K1−C43 3.344(2) Å, K1−C44 3.098(2) Å, K1−C45 3.152(2) Å) which prevents the formation of a coordination polymer, frequently observed for related potassium complexes based on I–IV [ 16a , 16b , 16d ] or H Dipp NacNac. [31]…”

“…On the basis of reported ( Z , Z )‐ and ( E , E )‐isomers of complex 8 – 10 and based on former gained knowledge of sterically less demanding bis(benzoxazol‐2‐yl)methanide potassium complexes[ 16a , 16b ] and their related 18‐crown‐6 derivatives,[ 16c , 16d , 38 ] we were curious whether the reaction of 8 with 18‐crown‐6 would prefer the formation of a ( Z , Z ), ( E , E ) or ( Z , E ) isomeric species. Therefore bis(4‐benzhydryl‐benzoxazol‐2‐yl)methane was first deprotonated with an excess of potassium hydride in THF at ambient temperature (Scheme 3 ).…”

s-Block cooperative catalysis: alkali metal magnesiate-catalysed cyclisation of alkynols

“…Although the crown ether is oen expected to sequester the alkali metal there are examples of structures where the alkali metal is still able to maintain p-interactions with the anionic moiety whilst coordinated by the crown ether. [71][72][73][74][75][76][77][78] Thus it appears that under these conditions, the addition of the crown ether must tune the coordination environment of K, modifying its Lewis acidity to generate a more catalytically competent species (vide infra). Therefore, these results suggest that the alkali metal is intimately involved and plays a key role in the cyclisation reaction.…”

Fast and Chemoselective Addition of Highly Polarized Lithium Phosphides Generated in Deep Eutectic Solvents to Aldehydes and Epoxides

“…By performing the deprotonation of HPPh 2 with solid hydrides (e. g., NaH, KH) in the absence of any volatile organic compound (VOC) under strict stoichiometric conditions, immediately followed by the addition of 2 a, adduct 3 a formed in remarkable 85-91 % yields (entries 4 and 5, Table 1). [30] Although similar yields were attained compared to n-BuLi, we decided to employ the latter in the further optimization of protocol design, especially because of the easier handle of stock solutions of this commercially available reagent.…”