Stable adducts L.SiCl4 (2), L.SiR2Cl2 (R = Me 3, Ph 4), and L.SnR2Cl2 (6) are formed by the reaction of the imidazol-2-ylidenes L (I; 1; R = Me, Et, Me2CH) with the corresponding Si and Sn halides. For L.SiCl4 (2b; L = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) and L.SnPh2Cl2 (6c; L = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) the monomeric nature of the compds. contg. pentacoordinated Si and Sn is established by x-ray structure analyses. The reaction of 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (1c) with SnCl2 gives the monomeric stannylene complex L.SnCl2 II (7c; L = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) whose mol. geometry indicates a weak C-to-Sn donor bond [Sn-C(1) 2.290(5) .ANG.].