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Combining variable-temperature infrared and NMR spectroscopic studies with quantum-chemical calculations (density functional theory (DFT) and natural bond orbital) allowed us to address the problem of competition between MH {M = transition metal) and BH hydrogens as proton-accepting sites in dihydrogen bond (DHB) and to unravel the mechanism of proton transfer to complex (PP3)RUH(#GH¹-BH4) (1, PP3 = K4-P(CH2CH2PPh2)3). Interaction of complex I with CH3OH, fluorinated alcohols of variable acid strength [CH2FCH2OH, CF,CH2OH, (CF3)2CHOH (HFIP), (CF3)3COH], and CF3COOH leads to the medium-strength DHB complexes involving BH bonds (3--5 kcal/mol), whereas DHB complexes with RuH were not observed experimentally. The two proton-transfer pathways were considered in DFT/M06 calculations. The first one goes via more favorable bifurcate complexes to BHterm and high activation barriers (38.2 and 28.4 kcal/mol in case of HF1P) and leads directly to the thermodynamic product [(PP3)RuHeq|(H2)]+[OR]-. The second pathway starts from the less-favorable complex with RuH ligand but shows a lower activation barrier (23.5 kcal/mol for HFIP) and eventually leads to the final product via the isomerization of intermediate [(PP3)RuHax(H2)]+[OR]-. The B--Hbr bond breaking is the common key step of all pathways investigated. [ABSTRACT FROM AUTHOR]

Ligand–metal cooperation: A new ligand–metal cooperating catalyst for the hydroformylation of olefins is described (see scheme). The mechanism of the H2 activation and CH bond formation of the catalyst involves an intramolecular cooperation between the structurally remote functionality and the metal center and proceeds without change of the oxidation state of the metal. [ABSTRACT FROM AUTHOR]

Research was conducted to examine the hydrogen bonding between the unsaturated 16-electron complex OsHCl(CO)(P(super t)Bu2Me2) and a sufficiently strong hydrogen bond donor. The objectives were to find the preferred accepting site and to determine the extent that the electronic structure of the complex can be modified through intermolecular hydrogen bonding. Results demonstrate the formation of a 1:1 adduct between OsHCl(CO)(P(super t)Bu2Me2) and (CF3)2(CHOH) in solution, bound exclusively through an (O)H***Cl(Os) hydrogen bond.

Abstract: The proton transfer from substituted phenols (ArOH= p-nitrophenol, p-nitophenyl-aza-phenol) to the ruthenium dihydride complex [(PP3)RuH2], where PP3 =P(CH2CH2PPh2)3, was studied by variable temperature UV–visible spectroscopy in dichloromethane, THF, THF/CH3OH and THF/CH3CN mixtures, showing a significant influence of the polarity and/or the proton donating/proton accepting properties of the solvent on the position of the proton transfer equilibrium. The formation of ion pairs stabilized by hydrogen bonding between the non-classical cation [(PP3)RuH(η2-H2)]+ and the homoconjugated anion [ArOHOAr]− was determined in low-polar media. The increase of the media polarity has been proved to favor the proton transfer leading to the dissociation of hydrogen bonded ion pairs [{(PP3) RuH(η2-H2)}+⋯{ArOHOAr}−]. Under comparable media polarity, the presence of a protic solvent in the mixture greatly favors the proton transfer due to the additional H-bonding with solutes. The structural, energetic and electronic features of the dihydrogen bonded adducts and of the proton transfer products were investigated by means of DFT/B3LYP calculations on the model dihydride [{P(CH2CH2PH2)3}RuH2] using CH3OH or CF3OH as proton donors. The specific and non-specific influence of the media properties on the dihydrogen bonding and proton transfer was studied by introducing the second protic (proton donor or solvent) molecule in the model system or by CPCM calculations. The additional participation of external molecules, from either the solvent or the alcohol, strengthens remarkably the dihydrogen bonded adducts and eases the proton transfer process. [Copyright &y& Elsevier]

Abstract: The interaction between Cp∗RuH(dppe) and a series of proton donors (HA) of increasing strength: CFH2CH2OH (MFE), CF3CH2OH (TFE), (CF3)2CHOH (HFIP), p-nitrophenol, CF3COOH and HBF4 has been investigated spectroscopically by variable-temperature IR, UV–Vis, and NMR spectroscopy in solvents of differing polarity (n-hexane, dichloromethane and their mixture). The low-temperature IR study shows the establishment of a hydrogen-bond which involves the hydride ligand as the proton accepting site. The basicity factor E j for the hydride was found to be 1.39. All techniques indicate that an equilibrium exists between the dihydrogen-bonded complex and the cationic dihydrogen complex, [Cp∗Ru(η2-H2)(dppe)]+, the formation of which is shown here for the first time. The proton transfer from HFIP is characterized by ΔH ∘ =−8.1±0.6kcalmol−1 and ΔS ∘ =−17±3eu. The activation parameters for the subsequent irreversible isomerization leading to the classical dihydride complex, [Cp∗Ru(H)2(dppe)]+, are ΔH ‡ =20.9±0.8kcalmol−1 and ΔS‡ =9±3eu as determined from 1H NMR spectroscopy for protonation by HBF4. Computational results at the DFT/B3PW91 level confirm the experimentally observed hydride basicity increase on descending the Group from iron to ruthenium and also the formation of the non-classical complex as an intermediate, prior to the thermodynamically favored dihydride. [Copyright &y& Elsevier]

The (carbonyl)dihydride complex [(triphos)Ru(CO)H[sub 2] ] (2) has been synthesized by reaction of the ruthenate [(triphos)RuH[sub 3] ]K (triphos = MeC(CH[sub 2] PPh[sub 2] )[sub 3] ) with ethanol saturated with CO. A single crystal X-ray analysis and IR and NMR experiments have shown that 2 adopts in both the solid state and solution an octahedral coordination geometry with a facial triphos ligand, two cis terminal hydrides, and a terminal carbonyl. The reaction of hexafluoro-2-propanol (HFIP) with 2 has been studied in CH[sub 2] Cl[sub 2] solution by IR and NMR spectroscopy. The proton donor interacts with a terminal hydride of 2 forming a rather strong hydrogen bond. The resulting H-bonded adduct [{(triphos)Ru(CO)(H)H}···{HOCH(CF[sub 3] )[sub 2] }] (2a) has fully been characterized by in situ NMR and IR techniques. Compound 2a is in equilibrium with the nonclassical η[sup 2] -H[sub 2] complex [(triphos)Ru(CO)H(H[sub 2] )][sup +] (2b), which can independently be prepared by protonation of 2 with a strong protic acid at low temperature. Unequivocal characterization of the dihydrogen complex (2b) has been achieved by a multifaceted spectroscopic investigation (T[sup obs] [sub 1min] = 0.005 s (200 MHz), J[sub H,D] 30 Hz, DQCC = 78.3 kHz). A combined IR and NMR study of the proton transfer reaction involving 2 and HFIP in CH[sub 2] Cl[sub 2 ] to give, first, the H-bonded adduct (2a) and, then, the dihydrogen complex (2b) has demonstrated that all these species are in equilibrium in the temperature range from 190 to 260 K. The thermodynamic parameters for the formation of 2a have independently been determined by NMR and IR methods, while those for the formation of 2b have been obtained by IR spectroscopy. An energetic profile for the reaction sequence 22a2b is proposed and discussed.Key words: hydrides, hydrogen bonding, ruthenium, IR spectroscopy, NMR spectroscopy.On a synthétisé le complexe [(triphos)Ru(CO)H[sub 2] ] (2) (triphos = MeC(CH[sub 2] PPh[sub 2] )[sub 3] ), un (carbonyl)dihydrure, en faisant réagir le ruthénate [(triphos)RuH[sub 3] ]K avec de l'éthanol saturé de CO. La diffraction des rayons X sur un cristal unique et des expériences d'IR et de RMN ont permis de montrer que le composé 2, tant à l'état solide qu'en solution, adopte une géométrie de coordination octaédrique comportant un ligand triphos facial, deux hydrures terminaux cis et un carbonyle terminal. Faisant appel à la spectroscopie IR et RMN, on a étudié la réaction du composé 2 avec l'hexafluoropropan-2-ol (HFIP) en solution dans le CH[sub 2] Cl[sub 2] . Le donneur de proton interagit avec un hydrure terminal du composé 2 en formant une liaison hydrogène relativement forte. Faisant appel in situ d'IR et de RMN, on a fait un caractérisation complète de l'adduit à liaison hydrogène qui en résulte [{(triphos)Ru(CO)(H)H}···{HOCH(CF[sub 3] )[sub 2] }] (2a). Le composé 2a est en équilibre avec le complexe non classique η[sup 2] -H[sub 2] , [(triphos)Ru(CO)(H[sub 2] )][sup +] (2b) que l'on peut préparer de façon indépendante en procédant à la protonation du composé 2 à l'aide d'un acide protique fort, à basse température. On a effectué la caractérisation non ambiguë du complexe dihydrogéné, 2b, en faisant appel à une étude spectroscopique à multiples facettes (T[sup obs] [sub 1min] = 0,005 s (200 MHz), J[sub H,D] 30 Hz, DQCC = 78,3 kHz). Faisant appel à une combinaison de techniques d'IR et de RMN, on a étudié la réaction de transfert de proton du composé 2 avec l'HFIP, dans le CH[sub 2] Cl[sub 2] , qui donne premièrement l'adduit à liaison hydrogène 2a et ensuite le complexe dihydrogéné 2b; ces études ont démontré que toutes ces espèces sont en équilibre sur toute la plage de températures allant de 190-260 K. Faisant appel à l'IR et à la RMN, on a déterminé de façon indépendante les paramètres thermodynamiques pour la formation du composé 2a alors que ceux pour la formation de 2b ont été obtenus par spectroscopie IR. On propose et on discute d'un profil énergétique pour la séquence des réactions 2 2a2b.Mots clés : hydrures, liaison hydrogène, ruthénium, spectroscopie IR, spectroscopie RMN.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]