The complex Ir2S2(PPh3)(4) (1) is known to react with 1 and 2 equivalents of H-2 leading to [Ir(H)(PPh3)(2)](2)(mu-S)(2) (2) and Ir-2(mu-S)(mu-SH)(mu-H)H-2(PPh3)(4) (4), respectively (Link, R. C.; Pafford, R. J.; Rauchfuss, T. B. J. Am. Chem. Soc. 2001, 123, 8856-8857). Herein, the results of a thorough computational (DFT) study of these formally homo- and heterolytic H2 activation processes, respectively, are presented. These indicate that 2 is formed in a two-step process whereby the oxidative addition of H-2 at a single Ir-II center of 1 generates an intermediate (A) that rearranges into 2 by means of a facile H migration to the neighboring Ir center. Activation of the second equivalent of H-2 most likely occurs at the bridging sulfur ligands of 2 leading to a reaction intermediate (3aa) that features two (mu-SH) ligands. Intermediate 3aa present two isomers that differ only on the stereochemistry of the (mu-SH) ligands, and both of them can further evolve into 4 via H migration from (mu-SH) to bridging (mu-H). Nevertheless, an alternative mechanism based on the initial isomerization of 2 into A, and followed by H-2 coordination and activation steps at a single Ir center cannot be completely ruled out. In general, the results herein show that the mechanisms for the activation of H-2 at 1 and 2 involve facile H migration processes, in agreement with the experimentally observed intermetallic hydride exchange in 2 and the exchange between IrH and SH centers in 4, which proceed with computed free energy barriers of ca. 19-23 kcal mol(-1).