Synthesis of a flexible macrocyclic tetraimidazolium salt-precursor for a tetracarbene ligand with metal dependent coordination modes

Schulte to Brinke C., Ekkehardt Hahn F. E.

Abstract

The cyclic tetraimidazolium salt (H4-4)(PF6)4 with flexible linkers between the imidazolium groups has been synthesized following a stepwise synthetic approach. In situ deprotonation of (H4-4)(PF6)4 in the presence of different metal ions leads to complexes where the tetracarbene ligand shows differing coordination modes depending on the metal center. Due to its high flexibility the tetracarbene ligand folds around d8 transition metal ions such as NiII, PdII and PtII to yield mononuclear tetracarbene complexes of type [M(4)](PF6)2 featuring a square-planar coordinated metal center. Reaction of 4 with metal centers that prefer a linear coordination mode such as AgI yields the tetranuclear silver(i) octacarbene complex [Ag4(4)2](PF6)4 featuring four silver(i) ions sandwiched in between two tetra-NHC ligands.