We report on the synthesis of N-heterocyclic tetrylenes ligated by the NON-donor framework 4,5-bis(2,6-diisopropylphenyl-amino)-2,7-di-tert-butyl-9,9-dimethylxanthene. The molecular structures of the germylene (3), stannylene (4) and plumbylene (5) where determined by X-ray diffraction studies. Furthermore, we present quantum chemical studies on the sigma-donor and pi-acceptor properties of 3-5. Additionally, we report on the reactivity of the tetrylenes towards the transition metal carbonyls [Rh(CO)(2)Cl](2), [W(CO)(6)] and [Ni(CO)(4)]. The isolated complexes (6 and 7) show the differing reactivity of NHTs compared to NHCs. Instead of just forming the anticipated complex [(NON)Sn-Rh(CO)(2)Cl], 4 inserts into the Rh-Cl bond to afford [(NON)Sn(Cl)Rh(CO)(C6H6)] (6, additional CO/C6H6 exchange) and [(NON)Sn(Cl)Rh-2(CO)(4)Cl] (7). By avoiding halogenated transition metal precursors in order to prevent insertion reactions, germylene 3 shows "classical" coordination chemistry towards {Ni(CO)(3)} forming the complex [(NON)Ge-Ni(CO)(3)] (8)
