Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone.

Anionic donor-functionalized NHC (N-heterocyclic carbene) complexes of Al are rare. We report one such case here, an NHC-aryloxido AlMe complex [Al(L)Me] (2), following a stepwise synthesis from the proligand [O-4,6-Bu-CH-2-CH{C(NCHCHNAr)}]Br [LBr; Ar = 2,6-Pr-CH (Dipp)] and AlMe the zwitterionic intermediate [Al(L)MeBr] (1). The ligand's flexibility in 2 is evident from the conformational fluxionality revealed by VT-H NMR spectroscopic analysis.

[(Flu)-(CH)-(NHC)-CH-(NHC)-(CH)-(Flu)]: an 'all-organic' hybrid and flexible ligand that enwraps a Ca pseudo-tetrahedrally.

A conformationally flexible ligand, [(Flu)-(CH)-(NHC)-CH-(NHC)-(CH)-(Flu)] (L), that offers four sequential organic donor modules and enwraps a Ca pseudo-tetrahedrally in a twisted 'S'-shape is devised. The [(L)Ca] synthesis is intriguingly stepwise involving the intermediate [(LH)Ca(HMDS)], whereas [(LH)Li(HMDS)] shows the potential for bimetallic chemistry. The bonding is illustrated by energy decomposition analyses.

Cyclopentadienyl Complexes of the Alkaline Earths in Light of the Periodic Trends.

The electron-rich cyclopentadienyl and the analogous indenyl and fluorenyl ligands (collectively denoted here as Cp') have been impactful in stabilizing electron-deficient metal centers including the highly electropositive alkaline earths. Being in the s-block, the group 2 metals follow a major periodic variation in their atomic and ionic properties which is reflected in those Cp' compounds. This article presents an overview of this class of compounds for all the five metals from beryllium to barium (radium is excluded for its radioactivity), highlighting their systematic variation.