The reactions of the trichloro carbyne complexes OsCl3(-CR)(PPh3)(2) (R = CH=CPh2, CH2Ar) with bromine and hydrogen peroxide were studied. Unlike monochloro carbyne complexes OsCl3( CR)(PPh3)(2), do not undergo oxidation reactions at the metal center or the metal carbyne bond. Treatment of OsCl3( CCH=CPh2)(PPh3)(2) with Br-2/H2O and H2O2/HCl produced OsBr3( CCH=CPh2)(H2O)(PPh3) and OsCl3( CCCl=CPh2)(PPh3)(2), respectively. Reactions of OsCl3( CCH2-C6H4-p-R)(PPh3)(2), (R = H, CMe3) with H2O2/HCl or H2O2 gave OsCl3{ CC(O)-C6H4-p-R}(PPh3)(2). Computational studies suggest that the difference in the reactivity of OsCl(=CAr)(CO)(PPh3), and OsCl3( CR)(PPh3)(2) is mainly of thermodynamic origin.