Carbon dioxide hydrogenation catalyzed by a ruthenium dihydride: a DFT and high-pressure spectroscopic investigation.

Reaction pathways during CO(2) hydrogenation catalyzed by the Ru dihydride complex [Ru(dmpe)(2)H(2)] (dmpe=Me(2)PCH(2)CH(2)PMe(2)) have been studied by DFT calculations and by IR and NMR spectroscopy up to 120 bar in toluene at 300 K. CO(2) and formic acid readily inserted into or reacted with the complex to form formates. Two formate complexes, cis-[Ru(dmpe)(2)(OCHO)(2)] and trans-[Ru(dmpe)(2)H(OCHO)], were formed at low CO(2) pressure (<5 bar). The latter occurred exclusively when formic acid reacted with the complex. A RuHHOCHO dihydrogen-bonded complex of the trans form was identified at H(2) partial pressure higher than about 50 bar. The trans form of the complex is suggested to play a pivotal role in the reaction pathway. Potential-energy profiles along possible reaction paths have been investigated by static DFT calculations, and lower activation-energy profiles via the trans route were confirmed. The H(2) insertion has been identified as the rate-limiting step of the overall reaction. The high energy of the transition state for H(2) insertion is attributed to the elongated Ru--O bond. The H(2) insertion and the subsequent formation of formic acid proceed via Ru(eta(2)-H(2))-like complexes, in which apparently formate ion and Ru(+) or Ru(eta(2)-H(2))(+) interact. The bond properties of involved Ru complexes were characterized by natural bond orbital analysis, and the highly ionic characters of various complexes and transition states are shown. The stability of the formate ion near the Ru center likely plays a decisive role for catalytic activity. Removal of formic acid from the dihydrogen-bonded complex (RuHHOCHO) seems to be crucial for catalytic efficiency, since formic acid can easily react with the complex to regenerate the original formate complex. Important aspects for the design of highly active catalytic systems are discussed.

[1]  Clark R. Landis,et al.  Valency and Bonding: Contents , 2005 .

[2]  H. Berke,et al.  Spectroscopic Evidence for Intermolecular M−H···H−OR Hydrogen Bonding: Interaction of WH(CO)2(NO)L2 Hydrides with Acidic Alcohols , 1996 .

[3]  J. E. Lyons,et al.  Catalysis research of relevance to carbon management: progress, challenges, and opportunities. , 2001, Chemical reviews.

[4]  Brett Clark,et al.  Carbon metabolism: Global capitalism, climate change, and the biospheric rift , 2005 .

[5]  M. Hidai,et al.  Hydrogenolyse von Trimethylsilylenolethern unter Verwendung eines sauren Rutheniumdiwasserstoff‐Komplexes als Katalysator , 1999 .

[6]  Y. Inoue,et al.  Synthesis of formates from alcohols, carbon dioxide, and hydrogen catalysed by a combination of group VIII transition-metal complexes and tertiary amines , 1975 .

[7]  S. Sakaki,et al.  Theoretical study of rhodium(III)-catalyzed hydrogenation of carbon dioxide into formic acid. Significant differences in reactivity among rhodium(III), rhodium(I), and ruthenium(II) complexes. , 2002, Journal of the American Chemical Society.

[8]  K. Nicholas,et al.  Rhodium-catalyzed hydrogenation of carbon dioxide to formic acid , 1992 .

[9]  Z. Yiping,et al.  Silica Immobilized Ruthenium Catalyst for Formic Acid Synthesis from Supercritical Carbon Dioxide Hydrogenation II: Effect of Reaction Conditions on the Catalyst Performance , 2005 .

[10]  Unfccc Kyoto Protocol to the United Nations Framework Convention on Climate Change , 1997 .

[11]  S. Sakaki,et al.  Theoretical Study of Ruthenium-Catalyzed Hydrogenation of Carbon Dioxide into Formic Acid. Reaction Mechanism Involving a New Type of σ-Bond Metathesis , 2000 .

[12]  Philip G. Jessop,et al.  Recent advances in the homogeneous hydrogenation of carbon dioxide , 2004 .

[13]  Yehoshoa Ben‐David,et al.  Complexation of N2, H2, CO2, and Ethylene to a T-Shaped Rhodium(I) Core , 1996 .

[14]  M. T. Bautista,et al.  Preparation and spectroscopic properties of the .eta.2-dihydrogen complexes [MH(.eta.2-H2)PR2CH2CH2PR2)2] + (M = iron, ruthenium; R = Ph, Et) and trends in properties down the iron group triad , 1991 .

[15]  A. Becke Density-functional thermochemistry. III. The role of exact exchange , 1993 .

[16]  W. Leitner,et al.  Direct formation of formic acid from carbon dioxide and dihydrogen using the [{Rh(cod)Cl}2]–Ph2P(CH2)4PPh2 catalyst system , 1992 .

[17]  P. Jessop,et al.  HOMOGENEOUS CATALYSIS IN SUPERCRITICAL FLUIDS : HYDROGENATION OF SUPERCRITICAL CARBON DIOXIDE TO FORMIC ACID, ALKYL FORMATES, AND FORMAMIDES , 1996 .

[18]  P. Jessop,et al.  Homogeneous catalytic hydrogenation of supercritical carbon dioxide , 1994, Nature.

[19]  Zhongyuan Zhou,et al.  Synthesis, characterization and reactivity of heterobimetallic complexes (η5-C5R5)Ru(CO)(μ-dppm)M(CO)2(η5-C5H5)(R = H, CH3; M = Mo, W). Interconversion of hydrogen/carbon dioxide and formic acid by these complexes , 2003 .

[20]  P. Jessop,et al.  Hydrogenation of carbon dioxide catalyzed by ruthenium trimethylphosphine complexes: the accelerating effect of certain alcohols and amines. , 2002, Journal of the American Chemical Society.

[21]  A. Merbach,et al.  The Slowest Water Exchange at a Homoleptic Mononuclear Metal Center: Variable-Temperature and Variable-Pressure 17O NMR Study on [Ir(H2O)6]3+ , 1996 .

[22]  J. E. Jackson,et al.  Dihydrogen bonding: structures, energetics, and dynamics. , 2001, Chemical reviews.

[23]  A. George,et al.  Bis(acetylide) complexes of ruthenium , 1996 .

[24]  R. Morris,et al.  Mechanisms of the H2-hydrogenation and transfer hydrogenation of polar bonds catalyzed by ruthenium hydride complexes , 2004 .

[25]  M. Voges,et al.  RHENIUM DIHYDROGEN COMPLEXES WITH ISONITRILE COLIGANDS : NOVEL DISPLACEMENT OF CHLORIDE BY HYDROGEN , 1996 .

[26]  Kwok‐yin Wong,et al.  Intramolecular N−H···H−Ru Proton−Hydride Interaction in Ruthenium Complexes with (2-(Dimethylamino)ethyl)cyclopentadienyl and (3-(Dimethylamino)propyl)cyclopentadienyl Ligands. Hydrogenation of CO2 to Formic Acid via the N−H···H−Ru Hydrogen-Bonded Complexes , 1998 .

[27]  W. R. Wadt,et al.  Ab initio effective core potentials for molecular calculations. Potentials for K to Au including the outermost core orbitals , 1985 .

[28]  W. Leitner The coordination chemistry of carbon dioxide and its relevance for catalysis: a critical survey , 1996 .

[29]  A. Baiker Utilization of carbon dioxide in heterogeneous catalytic synthesis , 2000 .

[30]  Michele Aresta,et al.  The contribution of the utilization option to reducing the CO2 atmospheric loading: research needed to overcome existing barriers for a full exploitation of the potential of the CO2 use , 2004 .

[31]  J. Grunwaldt,et al.  High pressure view-cell for simultaneous in situ infrared spectroscopy and phase behavior monitoring of multiphase chemical reactions , 2003 .

[32]  P. Jessop,et al.  Catalytic Production of Dimethylformamide from Supercritical Carbon Dioxide , 1994 .

[33]  P. Jessop,et al.  Homogeneous Catalysis in Supercritical Fluids , 1995, Science.

[34]  G. Kubas Catalytic Processes Involving Dihydrogen Complexes and Other Sigma-bond Complexes , 2005 .

[35]  W. Leitner,et al.  Activation of carbon dioxide: IV. Rhodium-catalysed hydrogenation of carbon dioxide to formic acid☆ , 1994 .

[36]  W. Leitner,et al.  Mechanistic Aspects of the Rhodium-Catalyzed Hydrogenation of CO2 to Formic AcidA Theoretical and Kinetic Study†,‖ , 1997 .

[37]  R. Noyori,et al.  Mechanism of asymmetric hydrogenation of ketones catalyzed by BINAP/1,2-diamine-rutheniumII complexes. , 2003, Journal of the American Chemical Society.

[38]  T. Hambley,et al.  Formation of ruthenium thiolates via complexes of molecular hydrogen , 1994 .

[39]  Clark R. Landis,et al.  Valency and Bonding: Author index , 2005 .

[40]  P. Jessop,et al.  Hydrogenation of carbon dioxide catalyzed by ruthenium trimethylphosphine complexes — Effect of gas pressure and additives on rate in the liquid phase , 2001 .

[41]  G. Laurenczy,et al.  Formation and characterization of water-soluble hydrido-ruthenium(II) complexes of 1,3,5-triaza-7-phosphaadamantane and their catalytic activity in hydrogenation of CO2 and HCO3- in aqueous solution. , 2000, Inorganic chemistry.

[42]  A. Baiker,et al.  Highly active ruthenium complexes with bidentate phosphine ligandsfor the solvent-free catalytic synthesis of N,N-dimethylformamideand methyl formate , 1997 .

[43]  P. Meakin,et al.  Stereochemically Nonrigid Six-Coordinate Molecules.' III. The Temperature-Dependent 'H and 31P Nuclear Magnetic Resonance Spectra of Some Iron and Ruthenium Dihydrides , 1973 .

[44]  Wang,et al.  Accurate and simple analytic representation of the electron-gas correlation energy. , 1992, Physical review. B, Condensed matter.

[45]  S. Scheiner,et al.  Activation and Cleavage of H-R Bonds through Intermolecular H...H Bonding upon Reaction of Proton Donors HR with 18-Electron Transition Metal Hydrides , 1999 .

[46]  S. Sakaki,et al.  Ruthenium(II)-catalyzed hydrogenation of carbon dioxide to formic acid. Theoretical study of real catalyst, ligand effects, and solvation effects. , 2005, Journal of the American Chemical Society.

[47]  S. F. Boys,et al.  The calculation of small molecular interactions by the differences of separate total energies. Some procedures with reduced errors , 1970 .

[48]  Iwao Omae,et al.  Aspects of carbon dioxide utilization , 2006 .

[49]  R. Perutz,et al.  FACILE INSERTION OF CO2 INTO THE RU-H BONDS OF RU(DMPE)2H2 (DMPE = ME2PCH2CH2PME2) : IDENTIFICATION OF THREE RUTHENIUM FORMATE COMPLEXES , 1996 .

[50]  Y. Inoue,et al.  CATALYTIC FIXATION OF CARBON DIOXIDE TO FORMIC ACID BY TRANSITION-METAL COMPLEXES UNDER MILD CONDITIONS , 1976 .

[51]  G. Müller,et al.  The Scientific Basis , 1995 .