Computational Insights on the Mechanism of H2 Activation at Ir2S2(PPh3)4: A Combination of Multiple Reaction Pathways Involving Facile H Migration Processes
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- 作者：Andrés G. Algarra
- 刊名：Inorganic Chemistry
- 出版年：2017
- 出版时间：January 3, 2017
- 年：2017
- 卷：56
- 期：1
- 页码：186-196
- 全文大小：596K
- ISSN：1520-510X
文摘
The complex Ir2S2(PPh3)4 (1) is known to react with 1 and 2 equivalents of H2 leading to [Ir(H)(PPh3)2]2(μ-S)2 (2) and Ir2(μ-S)(μ-SH)(μ-H)H2(PPh3)4 (4), respectively (group xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:ACS="http://namespace.acs.org/2008/acs" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">hlFld-ContribAuthor ">Linck, R. C.; hlFld-ContribAuthor ">Pafford, R. J.; hlFld-ContribAuthor ">Rauchfuss, T. B. group> J. Am. Chem. Soc.http://www.w3.org/1998/Math/MathML" xmlns:ACS="http://namespace.acs.org/2008/acs" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:space="preserve"> 2001http://www.w3.org/1998/Math/MathML" xmlns:ACS="http://namespace.acs.org/2008/acs" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:space="preserve">, 123http://www.w3.org/1998/Math/MathML" xmlns:ACS="http://namespace.acs.org/2008/acs" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:space="preserve">, 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 H2 at a single IrII 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 H2 most 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 H2 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 H2 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.