Tosylhydrazones have been prepared from acylsilanes and -germanes. These may be converted in excellent yield by n-butyllithium to the metalloidal diazoalkanes under milder conditions than are required for the analogous carbon compounds. The diazoalkanes are far more stable than their carbon counterparts. These results, together with spectral shifts noted for the silyl and germyl compounds, are interpreted in terms of dπ–pπ bonding between the diazo group and the metalloid atom.