Can N-heterocyclic germylenes behave as Lewis acids - is there another side to Meller germylenes?

Abstract

N-Heterocyclic germylenes are known to exist in two structurally different forms, the planar Meller germylenes and the monoimino germylenes that feature an envelope structure. This essay reviews recent reports dealing with radical and cationic Meller type germylenes § featuring the monoimino germylene structure, discusses their transformations and relationships, and asks the question whether indeed N-heterocyclic germylenes can be turned into Lewis acids.© Versita Warsaw and Springer-Verlag Berlin Heidelberg.

N-Heterocyclic Germylenes NHGe – Old Trends and New Developments

“…This is emphasised by two NHGe moieties, the long known eight membered NHGe with an electrophilic germanium and double quinoxaline annelation [11] and the newly synthesised quinoxaline annelated NHGe [19] (see Fig. Both compounds are unstable and act as Lewis acids towards a suitable Lewis base (chloride, PMe 3 ) as predicted in a recent review [4]. Both compounds are unstable and act as Lewis acids towards a suitable Lewis base (chloride, PMe 3 ) as predicted in a recent review [4].…”

“…An interesting topic in recent years has been the influence of annelation on the electronic properties of the NHGe ligand [4,9,11,12,18] and its ligating ability [10,11,42,43].…”

“…Although the chemistry of NHGe is largely developed in the shadows of the vastly more popular homologous Wanzlick-Arduengo carbenes NHC, they have actually been longer known as free ligands [1] and show a more diverse chemistry [1][2][3][4]. NHGe can change the ring size without apparent loss in stability [1], alter the oxidation state on germanium without losing their -donor ability [4,5] and have recently begun to discover functionalisation, a trend that was started with NHC some ten years ago [6].…”