Theoretical Investigation of Iridium (II) Sulfides Ir2(?-S)2(PH3)4 AND Ir2(?-S)2(PPh3)4



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Density functional theory results of the electronic structure of an iridium sulfide, Ir_(2)S_(2)(PPh_(3))(4) (2), are presented here, along with a discussion of the reaction mechanism of dihydrogen activation on this sulfide. This Ir (II) sulfide shows unusual reactivity binding two equivalents of H(2). The first reaction was believed to be a homolytic cleavage of one H_(2), between the two iridium centers, which would produce the dihydride complex Ir_(2)(PPh_(3))(2)H(2)(?-S)(2) (3), while the second-product was believed to arise from heterolytic cleavage by (3) of a second H(2), between an iridium and a bridging-sulfur atom, which would produce Ir_(2)(?-S)(?-SH)(?-H)H_(2)(PPh_(3))(4) (4). Previously published crystal structures on (2) and (3) suggest that the there is a strong metal-metal bond in the Ir(II) d7 dimer, (2), and that this bond is surprisingly preserved in the first H(2) cleavage product, (3). We investigated the activation of H_(2) by this Ir(II) complex, and the corresponding model complex Ir_(2)(?-S)(2)(PH(3))(4), in order to determine the details of this pathway. Our proposed mechanism suggests that the activation of the first equivalent of hydrogen can be either heterolytic or hemolytic, leading to a species with a bridging hydride Ir_(2)H(?-S)(2)(?-H)(PPh(3))_(4) (3-brid) in which the metal-metal bond is preserved, while the second activation appears to be a heterolytic activation, which produces the final product (4).