title: Computational Insights on the Mechanism of H2Activation at Ir2S2(PPh3)4: A Combination of Multiple Reaction Pathways Involving Facile H Migration Processes.
abstract: The complex Ir2S2(PPh3)4(1) is known to react with 1 and 2 equivalents of H2leading to [Ir(H)(PPh3)2]2(μ-S)2(2) and Ir2(μ-S)(μ-SH)(μ-H)H2(PPh3)4(4), respectively ( Linck , 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 H2activation processes, respectively, are presented. These indicate that 2 is formed in a two-step process whereby the oxidative addition of H2at a single IrIIcenter 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 H2most likely occurs at the bridging sulfur ligands of 2 leading to a reaction intermediate (3aa) that features two (μ-SH) ligands. Intermediate 3aa present two isomers that differ only on the stereochemistry of the (μ-SH) ligands, and both of them can further evolve into 4 via H migration from (μ-SH) to bridging (μ-H). Nevertheless, an alternative mechanism based on the initial isomerization of 2 into A, and followed by H2coordination 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 H2at 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.
authors.affiliation: Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz , Apartado 40, Puerto Real, 11510 Cádiz, Spain.
authors.forename: Andrés G
authors.identifier: http://orcid.org/0000-0002-5062-2858
authors.initials: AG
authors.lastname: Algarra