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A review discussing the pressurization of organometallic systems in H2O. It deals with the effect of the high hydrostatic pressure on organometallics and the characterization of reactions involving pressurized gases with aq. organometallics.

A series of 'dual-functionalised' ionic liquids, comprising imidazolium cations with various functionalities and the nitrile functionalised anion [CH3H(BF3)CH2CN](-) have been prepared; some exhibit very low viscosities-a highly valuable property in many applications.

The new water-soluble ruthenium-nitrosyl complexes [RuCl3(NO)(TPPMS)(2)] and [RuCl3(NO)(TPPTS)(2)] were synthetized and characterized by IR, H-1 and P-31 NMR spectroscopies. The NO stretching frequencies, nu(NO) = 1870 cm(-1) (TPPMS) and 1883 cm(-1) (TPPTS) suggest a linear Ru-N-O arrangements. Reactions with OH- yield the corresponding [RuCl3 (NO2)(P)(2)] derivatives, furthermore, [RuH(NO)(P)(3)] is formed with TPPMS or TPPTS, respectively, under 100 bar H-2 pressure. The new complexes are suitable precatalysts for the hydrogenation of carbon dioxide and/or bicarbonate in aqueous solutions up to a turnover frequency of 400 h(-1) under relatively mild conditions (30 bar H-2, 70 degreesC). (C) 2003 Elsevier Science B.V. All rights reserved.

The water-soluble Ru(II)-phosphine complex, [{RuCl2(mTPPMS)(2)}(2)] was found a suitable catalyst for the hydrogenation of NaHCO3 to NaHCO2 in aqueous solution under mild conditions with catalyst turnover frequencies (TOFs) in the range of 35-50 h(-1) at 50degreesC and 10 bar total pressure. The suggested reaction mechanism involves the formation of Ru(II)-hydrides of the general formula [RuHX(mTPPMS)(4)] where X = H-, HCO3- or HCO2-. At 80degreesC and 95 bar total pressure, the reduction of NaHCO3 proceeded with high reaction rate (9600 h(-1)) hitherto unobserved in purely aqueous solutions. The reactions do not require the presence of organic amine additives, however, the addition of quinoline increased the rate considerably. Aqueous suspensions of calcium carbonate could also be hydrogenated with CO2/H-2 gas mixtures. (C) 2003 Elsevier B.V. All rights reserved.

In aqueous solutions under mild conditions, [Ru(H2O)(6)](2+) was reacted with various water-soluble tertiary phosphines. As determined by multinuclear NMR spectroscopy, reactions with the sulfonated arylphosphines L = mtppms, ptppms and mtppts yielded only the mono- and bisphosphine complexes, [Ru(H2O)(5)L](2+), cis-[Ru(H2O)(4)L-2](2+), and trans-[Ru(H2O)(4)L-2](2+) even in a high ligand excess. With the small aliphatic phosphine L = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1(3,7)]decane (pta) at [L] : [Ru] = 12 : 1, the tris- and tetrakisphosphino species, [Ru(H2O)(3)(pta)(3)](2+), [Ru(H2O)(2)(pta)(4)](2+), [Ru(H2O)(OH)(pta)(4)](+), and [Ru(OH)(2)(pta)(4)] were also detected, albeit in minor quantities. These results have significance for the in situ preparation of Ru(II)-tertiary phosphine catalysts. The structures of the complexes trans-[Ru(H2O)(4)(ptaMe)(2)](tos)(4).2H(2)O, trans-[Ru(H2O)(4)(ptaH)(2)](tos)(4).2H(2)O, and trans-mer-[RuI2(H2O)-(ptaMe)(3)]I-3.2H(2)O, containing protonated or methylated pta ligands (ptaH and ptaMe, respectively) were determined by single crystal X-ray diffraction.

In aqueous solutions, [RuCl2(TPPMS)(2)](2) (TPPMS = 3-sulfonatophenyldiphenylphosphine) catalyzes the exchange between H-2 and D2O or between D-4 and H2O with high efficiency (up to 1 252 turnovers per hour) under mild conditions (298 K, 2 MPa H-2). The exchange rate strongly depends on the solution pH. Similar H/D exchange is observed with the water soluble tertiary phosphine complexes [RhCl(TPPMS)(3)], [RhCl(TPPTS)(3)] and [RuCl2(PTA)(4)] as catalysts (TPPTS = tris(3-sulfonatophenyl)phosphine. PTA = 1,3,5-triaza-7-phosphadamantane) which, however, show lower activity. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.

This paper focuses on the mechanism by which a monoterpene undergoes a cyclocarbonylation reaction catalysed by a palladium complex. Evidence is provided, based on intermediate species observed under pressure or with various ligands, that the catalytic cycle follows a hydride route starting from [Pd(H)(SnCl3)L-2], The [Pd(H)(SnCl3)L-2] complexes (L = PPh3 or PCy3) have been observed for the first time by multinuclear NMR spectroscopy. Cationic hydride complexes or palladium(0) precursors show either no or poor reactivity. Studies related to model platinum complex chemistry have detected an acylplatinum species. Most of the observations have been done on the cyclocarbonylation of isopulegol, di-hydromyrcenol or isolimonene into the corresponding lactones or cyclopentanones. The use of dihydromyrcene allowed us to observe the acylplatinum complex and the corresponding elusive acylpalladium species. The co-catalytic role of SnCl2 is also demonstrated.

In a water/chlorobenzene biphasic reaction, the hydrogenation of trans-cinnamaldehyde, catalyzed by water-soluble Ru(II)-phosphane complexes at pH 3.04 (phosphate buffer), produces a 61:39 mixture of cinnamyl alcohol and dihydrocinnamaldehyde at 1 bar H-2; however, the selectivity is increased to 93:7 by increasing the hydrogen pressure to 8 bar.

The effect of pressure on the Diels-Alder reaction was examined in room temperature ionic liquids, followed by high-pressure FT-IR spectroscopy using pressures up to 150MPa. Pressure enhances the kinetic sensitivity of the reaction. The kinetic effect of fluorophobic interactions was examined using ionic liquids with fluorous cations. Ionic liquids in combination with ZnI2 as a Lewis acid catalyst were also studied under high pressure.

The synthesis of [PPN][IrRu3(CO)13] and [PPN][IrOs3(CO)13] from the reaction of [PPN][Ir(CO)4] with M3(CO)12 (M = Ru or Os) is discussed. [PPN][IrRu3(CO)13] is a red-brown microcryst. powder, while [PPN][IrOs3(CO)13] is an orange-red microcryst. powder. Both compds. appear to be stable toward air and moisture, but should be stored under N2. Both compds. are sol. in polar org. solvents such as Et2O, THF, CH2Cl2 or MeOH.

Formation of a vacant coordination site on a Ru center permits an unusual binding of small molecules such as ethylene, acetylene, and dihydrogen, resulting in the transformation of the chelating β-diketiminate ligand to a β-diimine. These representative species are observed during the catalytic hydrogenation of styrene.

Hydrolysis and hydrogenation of [RhCl(tppms)(3)] (1) and trans-[RhCl(CO)(tppms(2)] (2) was studied in aqueous solutions in a wide pH range (2 < pH < 11) in the presence of excess TPPMS (3 -diphenylphosphinyl-benzenesulfonic acid sodium salt). In acidic solutions hydrogenation of 1 yields a mixture of cis-mer- and cis;fac-[RhCIH2(tppms)(3)] (3a,b) while in strongly basic solutions [RhH(H2O)(tppms)(3)] (4) is obtained, the midpoint of the equilibrium between these hydride species being at pH 8.2. The paper gives the first successful H-1 and P-31 NMR spectroscopic characterization of a water soluble rhodium(I)-monohydride (4) bearing only monodentate phosphine ligands. Hydrolysis of 2 is negligible below pH 9 and its hydrogenation results in formation of [Rh(CO)H(tppms)(3)] (5), which is an analogue to the well known and industrially used hydroformylation catalyst [Rh(CO)H(tppts)(3)] (6) (TPPTS = 3,3',3"-phosphinetriyltris(benzenesul-fonic acid) trisodium salt). It was shown by pH-potentiometric measurements that formation of 5 is strongly pH dependent in the PH 5-9 range; this gives an explanation for the observed but previously unexplained pH dependence of several hydroformylation reactions. Conversely, the effect of pH on the rate of hydrogenation of maleic and fumaric acid catalyzed by 1 in the 2< pH < 7 range can be adequately described by considering solely the changes in the ionization state of these substrates. All these results warrant the use of buffered (pH-controlled) solutions for aqueous organometallic catalysis.

Hexafluoro-2-butyne, CF(3)Cequivalent toCCF(3), reacts with the triangulo-clusters [Pt-3 (mu-CO)(3)(PR3)(3)] to give the diplatinum(o) compounds [Pt-2(CO)(2)(PR3)(2)(mu-eta(2):eta(2)-CF(3)Cequivalent toCCF(3))] {PR3=PPh3 (1), PBzPh(2) (2), PCy3 (3), (PPr3)-Pr-i (4)}. Spectroscopic properties are reported which are in accord with the molecular structures for 1 and 3, both having the acetylenic C-C axis perpendicular to the Pt-Pt axis, bridging two [Pt(CO)(PR3)] fragments in a mu-eta(2):eta(2) fashion. A large excess of hexafluorobutyne slowly converts 1 and 2 to the diplatinum(II) complexes [Pt-2(CO)(2)(PR3)(2) (mu-eta(1):eta(1)-CF(3)Cequivalent toCCF(3))(2)]{PR3=PPh3 (5), PBzPh(2) (6)}, having two planar hexflauorobutyne bridges. This stereochemistry has been established by NMR and IR spectra, and confirmed by single-crystal X-ray diffraction.

The hexaaqua complex of ruthenium(II) represents an ideal starting material for the synthesis of isostructural compounds with a [Ru(H2O-ax)(H2O-eq)4L]2+ general formula. We have studied a series of complexes, where L = H2O, MeCN, Me2SO, H2CCH2, CO, and F2CCH2. We have evaluated the effect of L on the cyclic voltammetric response, on the rate and mechanism of exchange reaction of the water molecules, and on the structures calculated with the density functional theory (DFT). As expected, the formal redox potential, E°‘(+2/+3), increases with the π-accepting capabilities of the ligands. For L = N2, the oxidation to Ru(III) is followed by a fast substitution of dinitrogen by a solvent molecule, revealing the poor stability of the Ru(III)−N2 bond. The water exchange reactions have been followed by 17O NMR spectroscopy. The variable-pressure and variable-temperature kinetic studies made on selected examples are all in accordance with a dissociative activation mode for exchange. The positive activation volumes obtained for the axial and equatorial water exchange reactions on [Ru(H2O)5(H2CCH2)]2+ (ΔVax and ΔVeq = +6.5 ± 0.5 and +6.1 ± 0.2 cm3 mol-1) are the strongest evidence of this conclusion. The increasing cis-effect series was established according to the lability of the equatorial water molecules and is as follows: F2CCH2 CO < Me2SO < N2 < H2CCH2 < MeCN < H2O. The increase of the lability is accompanied by a decrease of the E°‘ values, but no change was found in the calculated Ru−H2Oeq bond lengths. The increasing trans-effect series, established from the lability of the axial water molecule, is the following: N2 MeCN < H2O < CO < Me2SO < H2CCH2 < F2CCH2. A variation of the Ru−H2Oax bond lengths is observed in the calculated structures. However, the best correlation is found between the lability and the calculated Ru−H2Oax bond energies. It appears, also, that a decrease of the electronic density along the Ru−Oax bond and the increase of the lability can be related to an increase of the π-accepting capability of the ligand. For L = N2, the calculations have shown that the Ru(II)−N2 bond is weak. Consequently, the water exchange reaction proceeds through a different mechanism, where first the N2 ligand is substituted by one water molecule to produce the hexaaqua complex of Ru(II). The water exchange takes place on this compound before re-formation of the [Ru(H2O)5N2]2+ complex.

This work reports the hydrogenation of carbon dioxide/inorganic carbonate salts to formic acid/formate in two phase systems comprising an ionic phase, in which the catalyst is immobilized, and an aqueous phase in which the carbonates and formate are confined, is reported. The reactions were followed in situ by multinuclear NMR. Pressurized H-2 gas was used for the reduction.

[Rh-4 (CO)(6) (mu-Me2PCH2PMe2)(3)], the first example of a hexasubstituted derivative of Rh-4(CO)(12), has a ground state geometry in the solid state and in solution of C-s symmetry with four edge-bridging carbonyls and with each diphosphine ligand bridging one edge of the same Rh-3 face. The result is an imbalance of the formal electron count at two rhodium atoms. As observed by C-13- and P-31-NMR, the mobility of the ligands is restricted to one mu-CO eta-CO site exchange which astonishingly does not average dynamically the electron count on all four metal atoms.