Seiji Ogo

Models of the active site in [NiFe]hydrogenase enzymes have proven challenging to prepare. We isolated a paramagnetic dinuclear nickel-ruthenium complex with a bridging hydrido ligand from the heterolytic cleavage of H2 by a dinuclear NiRu aqua complex in water under ambient conditions (20 degrees C and 1 atmosphere pressure). The structure of the hexacoordinate Ni(mu-H)Ru complex was unequivocally determined by neutron diffraction analysis, and it comes closest to an effective analog for the co

Chemists have long sought to mimic enzymatic hydrogen activation with structurally simpler compounds. Here, we report a functional [NiFe]-based model of [NiFe]hydrogenase enzymes. This complex heterolytically activates hydrogen to form a hydride complex that is capable of reducing substrates by either hydride ion or electron transfer. Structural investigations were performed by a range of techniques, including x-ray diffraction and neutron scattering, resulting in crystal structures and the find

Ruthenium aqua complexes [(eta(6)-C(6)Me(6))Ru(II)(L)(OH(2))](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))](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 cataly

An acid-stable hydride complex [Cp*IrIII(bpy)H]+ {1, Cp* = eta5-C5Me5, bpy = 2,2'-bipyridine} serves as the active catalyst for the highly chemoselective synthesis of alpha-amino acids by reductive amination of alpha-keto acids with aqueous NH3 and HCOO- in water at pH 5-8. pH-dependent catalytic 15N- and 2H-double-labeling has also been accomplished by using 15NH3 and DCOONa, which are ideal amine and hydride ion sources, respectively.

The paper reports on the development of a new class of water-soluble organometallic catalysts for pH-dependent transfer hydrogenation. An organometallic aqua complex [(η6-C6Me6)RuII(bpy)(H2O)]2+ (1, bpy = 2,2‘-bipyridine) acts as a catalyst precursor for pH-dependent transfer hydrogenation of water-soluble and -insoluble ketones with HCOONa as a hydrogen donor in water and in biphasic media. Irrespective of the solubility of the ketones toward water, the rate of the transfer hydrogenation shows

This paper reports a pH-dependent hydrogenation of water-soluble carbonyl compounds by hydrogen transfer from HCOONa as a hydrogen source (transfer hydrogenation) promoted by [Cp*IrIII(H2O)3]2+ (1, Cp* = η5-C5Me5) as a catalyst precursor in water. Complex 1 has been characterized by X-ray structure analysis, 1H NMR, and potentiometric titration experiments. The active catalyst, a dinuclear μ-hydride complex [(Cp*IrIII)2(μ-H)(μ-OH)(μ-HCOO)]+ (2), has been isolated and characterized by 1H NMR, IR,

This paper reports pH-dependent transfer hydrogenation, reductive amination, and dehalogenation of water-soluble substrates with the organometallic aqua complexes [Cp*IrIII(H2O)3]2+ (1, Cp* = η5-pentamethylcyclopentadienyl), [(Cp∧py)IrIII(H2O)2]2+ (2, Cp∧py = η5-(tetramethylcyclopentadienyl)methylpyridine), and [Cp*IrIII(bpy)(H2O)]2+ (3, bpy = 2,2'-bipyridine) as catalyst precursors and the formate ions HCOONa and HCOONH4 as hydrogen donors. Because of the difference in the electron-donating abi

Hydrogenation of carbon dioxide (P(H2/CO2)= 5.5/2.5 MPa) into formic acid (HCOOH) under acidic conditions (pH 2.5-5.0) in water has been achieved by using water-soluble ruthenium aqua catalysts [(eta6-C6Me6)RuII(L)(OH2)]SO4 (L = 2,2'-bipyridine or 4,4'-dimethoxy-2,2' bipyridine).

This review discusses the development of aqueous phase, homogeneous, transfer hydrogenation catalysis. Transfer hydrogenation catalysts, based on Ru, Ir and Rh, reduce organic substrates in water by assisting the transfer of hydrogen from simple donor species. These catalysts are expected to have significant benefits when compared with organic phase catalysts, including greater activity, greater selectivity and smaller environmental impact. They will therefore be expected to make a significant c

The growing need for hydrogen-based fuel cells has driven research into hydrogenase (H(2)ase)-a natural enzyme that catalyses the extraction of electrons from H(2) in water under ambient conditions. Unfortunately, the exact mechanism by which H(2)ase achieves this feat has remained a matter of some controversy until now, with many mechanisms being inconsistent with experimental data. Recently, however, we have been able to produce a successful catalytic mimic of H(2)ase that replicates key aspec

The series of water-soluble palladacyclic aqua complexes [(tBu-SCS)PdII(H2O)]+ ([1]+, tBu-SCS = C6H3-2,6-(CH2StBu)2), [(iPr-SCS)PdII(H2O)]+ ([2]+, iPr-SCS = C6H3-2,6-(CH2SiPr)2), [(PCP)PdII(H2O)]+ ([3]+, PCP = C6H3-2,6-(OPiPr2)2), and [(PC)PdII(H2O)2]+ ([4]+, PC = 4-MeC6H3-2-(OPiPr2)) have been synthesized from the reaction of the corresponding palladacyclic chloro complexes with silver salts in water to optimize the catalytic activity for pH-dependent C−C coupling reactions in water by changing

The cis configuration between the hydroxo and the carboxylato and the three amino groups of the tetradentate, tripodal ligand tris(6-neopentylamino-2-pyridylmethyl)amine favors the formation of hydrogen bonds which stabilize the hydroxo-Feⁱⁱⁱ complex 1. Thus, its structure closely resembles that of the active center of Feⁱⁱⁱ -soybean lipoxygenase-1, which also contains a six-coordinate Feⁱⁱⁱ atom.

NAD⁺ (oxidized form of NAD:nicotinamide adenine dinucleotide)-reducing soluble [NiFe]-hydrogenase (SH) is phylogenetically related to NADH (reduced form of NAD⁺):quinone oxidoreductase (complex I), but the geometrical arrangements of the subunits and Fe-S clusters are unclear. Here, we describe the crystal structures of SH in the oxidized and reduced states. The cluster arrangement is similar to that of complex I, but the subunits orientation is not, which supports the hypo