In comparison to β-diketiminates, a highly exploited class of N,N-chelating ligands, the corresponding βthioketoiminates, monothio-substituted analogues, have received only minor attention. β-Thioketoiminates are straightforwardly prepared through treatment of an appropriate β-ketoiminate with Lawesson's reagent. Employing standard synthetic techniques for η 6 -arene Ru(II) and Os(II) β-diketiminate complexes, an analogous series of chlorido-metal complexes supported by different sized N-aryl substituted β-thioketoiminate ligands is reported. However, metal ligation of a β-thioketoiminate bearing an electron-withdrawing CF 3 group was not possible. The metal− chlorine bond in these complexes is readily activated by various sodium or silver salts of weakly coordinating anions, affording coordinately unsaturated cationic formally 16-electron species. All η 6 -C 6 H 6 metal β-thioketoiminate complexes were characterized by NMR and in the solid state using single crystal X-ray diffraction techniques. Structural studies reveal that incorporation of a thio-group induces substantial bond angle distortion within the metallocycle. The reactivity of the cationic η 6 -C 6 H 6 Ru(II) β-thioketoiminate complexes toward alkynes and isonitriles is analogous to that of the β-diketiminate species. Specifically, the reaction with 1-hexyne results in a [4 + 2] cycloaddition involving the metal and β-C sites, while reaction with isonitrile completely displaces the η 6 -C 6 H 6 ligand. A comprehensive DFT study employing charge decomposition analysis (CDA) reveals a strong covalent metal−sulfur bond which dominates the metal β-thioketoiminate interaction. The M−S bond (M = Ru or Os) is strengthened by charge transfer from metal to sulfur, in contrast to the β-diketiminate species where back electron donation from the metal to the nitrogen centers is negligible. The first reported β-selenoketoiminate was prepared by reacting a β-ketoiminate with the Woolins' reagent. However, this seleno-analog demonstrated significant instability with respect to hydrolysis, and coordination to an η 6 -arene Ru(II) or Os(II) moiety proved unsuccessful.