New Pt₂(III,III)X₂ half-lantern compounds resulted in the C?X bond activation in haloalkanes (CHCl₃,CHBr₃, CHI₃, or CH₃I) by the corresponding Pt₂(II,II) derivative. Mechanistic studies using ¹³CH₃I revealed that this reaction initiates with the thermal oxidative addition to render [I(bzq)Pt(μ-N^S)₂Pt(bzq)(¹³CH₃)], which photochemically transforms into [Pt₂(bzq)₂(μ-N^S)₂I₂]. In the presence of O₂, the methylperoxo intermediate [I(bzq)Pt(μ-N^S)₂Pt(bzq)(O-O¹³CH₃)}] was detected, which, in the presence of ¹³CH₃I, renders the final product together with ¹³CH₃OH