Ogo Seiji, Kabe Ryota, Hayashi Hideki, Harada Ryosuke, Fukuzumi Shunichi
Center for Future Chemistry, Kyushu University, Nishi-ku, Fukuoka, 819-0395, Japan.
Dalton Trans. 2006 Oct 21(39):4657-63. doi: 10.1039/b607993h. Epub 2006 Aug 16.
Ruthenium aqua complexes (eta(6)-C(6)Me(6))Ru(II)(L)(OH(2)) {L = bpy (1) and 4,4'-OMe-bpy (2), bpy = 2,2'-bipyridine, 4,4'-OMe-bpy = 4,4'-dimethoxy-2,2'-bipyridine} and iridium aqua complexes Cp*Ir(III)(L)(OH(2)) {Cp* = eta(5)-C(5)Me(5), L = bpy (5) and 4,4'-OMe-bpy (6)} act as catalysts for hydrogenation of CO(2) into HCOOH at pH 3.0 in H(2)O. The active hydride catalysts cannot be observed in the hydrogenation of CO(2) with the ruthenium complexes, whereas the active hydride catalysts, Cp*Ir(III)(L)(H) {L = bpy (7) and 4,4'-OMe-bpy (8)}, have successfully been isolated after the hydrogenation of CO(2) with the iridium complexes. The key to the success of the isolation of the active hydride catalysts is the change in the rate-determining step in the catalytic hydrogenation of CO(2) from the formation of the active hydride catalysts, (eta(6)-C(6)Me(6))Ru(II)(L)(H), to the reactions of Cp*Ir(III)(L)(H) with CO(2), as indicated by the kinetic studies.
钌水配合物[(η⁶-C₆Me₆)Ru(II)(L)(OH₂)]²⁺ {L = 联吡啶(bpy, 1)和4,4'-二甲氧基联吡啶(4,4'-OMe-bpy, 2)，bpy = 2,2'-联吡啶，4,4'-OMe-bpy = 4,4'-二甲氧基-2,2'-联吡啶}以及铱水配合物[CpIr(III)(L)(OH₂)]²⁺ {Cp = η⁵-C₅Me₅，L = bpy (5)和4,4'-OMe-bpy (6)}在pH为3.0的水中作为将CO₂氢化为HCOOH的催化剂。在用钌配合物催化CO₂氢化反应中无法观察到活性氢化物催化剂，而在用铱配合物催化CO₂氢化反应后成功分离出了活性氢化物催化剂[CpIr(III)(L)(H)]⁺ {L = bpy (7)和4,4'-OMe-bpy (8)}。动力学研究表明，成功分离活性氢化物催化剂的关键在于催化氢化CO₂的速率决定步骤从活性氢化物催化剂[(η⁶-C₆Me₆)Ru(II)(L)(H)]⁺的形成转变为[CpIr(III)(L)(H)]⁺与CO₂的反应。
