Stable imidazol-2-ylidene-borane adducts I (X = H, F, R1 = Me, Et, CHMe2, R2 = Me) are obtained from 1,3,4,5-tetraalkylimidazol-2-ylidenes 7 and Me2S.BH3 or Et2O.BF3. The structure of I (X = H, R1 = Et, R2 = Me) was detd. by x-ray crystallog. An ab initio calcn. [MP2(fu)/6-31G**] reveals a low energy difference between two rotamers. The bond orders of the cyclic bonds imply only a minor p interaction between the N-C-N and the C-C fragment.