The reactions of stable β-diketiminate tin(II) dimethylamide LSnNMe2 [L = HC(CMeNAr)2; Ar = 2,6-iPr2C6H3] (1) with ketones and activated terminal alkynes are described. 1 reacts with 2-benzoylpyridine and 2,2,2-trifluoroacetophenone to give the tin(II)-alkoxides LSnOCPh(2-Py)NMe2 (2) and LSnOCPh(CF3)NMe2 (3), respectively, by nucleophilic addition of the dimethylamido group to the carbonyl moiety. Furthermore, the reaction of 1 with terminal alkynes (HCCCO2R, R = Me, Et) forms tin(II)-alkynyl LSnCCCO2R (R = Me, (4); R = Et, (5)) compounds under elimination of Me2NH rather than undergoing a nucleophilic addition reaction at the carbon–carbon triple bond. Compounds 2–5 were characterized by microanalysis and multinuclear NMR spectroscopy. Moreover, 2 and 5 could be crystallized and their constitutions were confirmed by X-ray structural analysis. 2 and 5 are monomers in the solid state and the metal atom shows a distorted trigonal-pyramidal coordination sphere.