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RuO2@SiO2nanomaterials are prepared using hybrid mesostructured silica (EtO)2P(O)(CH2)3SiO1.5/xSiO2(x= 9, 16) by anchoring the metal precursor [Ru(COD)(COT)] (COD is 1,3‐cyclooctadiene, COT is 1,3,5‐cyclooctatriene) inside the pores of the organized silica matrix through the phosphonate moieties. Following this task, the nanoparticles are fabricated by i) decomposing the metal precursor with hydrogen at room temperature in tetrahydrofuran to achieve ruthenium nanoparticles and ii) thermally treating the ruthenium particles in silica at 450 °C in air to fabricate RuO2. The materials containing Ru and RuO2nanoparticles are characterized by elemental analysis, transmission electron microscopy (TEM), X‐ray diffraction (XRD), nitrogen sorption measurements, and 31P and 13C NMR. The obtained RuO2@SiO2nanomaterials are evaluated as catalytic filters when deposited onto gas sensors for the preferential detection of propane in the multicomponent gas mixture propane/carbon monoxide/nitrogen dioxide.

In this paper a quantitative explanation for a diamagnetic orthoparaH2conversion is given. The description is based on the quantum-mechanical density matrix formalism originally developed by Alexander and Binsch for studies of exchange processes in NMR spectra. Only the nuclear spin system is treated quantum-mechanically. Employing the model of a three spin system, the reactions of the hydrogen gas with the catalysts are treated as a phenomenological rate process, described by a rate constant. Numerical calculations reveal that for nearly all possible geometrical arrangements of the three spin system an efficient spin conversion is obtained. Only in the chemically improbable case of a linear group H–X–H no spin conversion is obtained. The efficiency of the spin conversion depends strongly on the lifetime of the H–X–H complex and on the presence of exchange interactions between the two hydrogens. Even moderate exchange couplings cause a quench of the spin conversion. Thus a sufficiently strong binding of the dihydrogen to the Sspin is necessary to render the quenching by the exchange interaction ineffective.

The bis(dihydrogen) complex RuH2(η²-H2)2(PCy3)2 (1) reacts at room temperature with 1 equiv of either HBpin or HBcat to produce the σ-borane complexes RuH2(η²-HBpin)(η²-H2)(PCy3)2 (2Bpin) and RuH2(η²-HBcat)(η²-H2)(PCy3)2 (2Bcat), respectively, by substitution of one σ-H2 ligand by one σ-B−H. In contrast, when using the 9-BBN reagent, the dihydridoborate complex RuH[(μ-Η)2BBN](η²-H2)(PCy3)2 (2BBN) is formed. The coordination modes of the borane ligands have been ascertained by NMR spectroscopy, X-ray diffraction, and theoretical studies (DFT/B3LYP). The results indicate that the dialkoxyborane ligands (HBpin and HBcat) are not acidic enough to stabilize a “true” symmetrical dihydridoborate coordination mode. They thus lead to σ-borane complexes presenting a small H/BH cis interaction between the boron atom and the adjacent hydride. The σ-H2 ligand in 2Bpin is located by X-ray diffraction at 90 K and found to be perpendicular to the equatorial plane. DFT calculations lead to the optimization of the two degenerate isomers RuH2[η²-HB(OCH2)2](η²-H2)(PMe3)2 (5Bpin_a) (analogous to 2Bpin) and RuH[(μ-H)2B(OCH2)2](η²-H2)(PMe3)2 (5Bpin_b), demonstrating that σ-H2 rotation and σ-borane versus dihydridoborate ligation are intimately correlated. In contrast, the 9-BBN reagent is a strong Lewis acid and leads to a dihydridoborate complex. The theoretical study on RuH[(μ-Η)2Bpin](η²-HBpin)(PCy3)2 (3Bpin) shows that the bonding is also dependent on the hydride basicity:  the RuH[(μ-H)2B(OCH2)2](PMe3)2 fragment used as a model for RuH[(μ-Η)2Bpin](PCy3)2 is not basic enough to contain a second ligand bound in a dihydridoborate mode, despite the stabilization that should be gained from the resulting symmetrical structure.

Oxide-free cobalt nanoparticles (NPs) of 2.5−3 nm diameter have been synthesized in the presence of di-isobutyl aluminum hydride (DiBAH), a potential alumina source, from two different precursors:  Co(η³C8H13)(η⁴C8H12) and Co[N(SiMe3)2]2. The NPs display very different structural and magnetic features, which are related to the difference in chemical environment at the NPs surface.

A series of ortho-metalated ruthenium hydrido dihydrogen complexes of the form RuH(H2)(X)(PⁱPr3)2 (X = 2-phenylpyridine (ph-py) (2), benzoquinoline (bq) (3), phenylpyrazole (ph-pz) (4)) were prepared by adding 1 equiv of the corresponding substrate X−H and 2 equiv of PⁱPr3 to Ru(COD)(COT) under 3 bar of H2. The analogous complex RuH(H2)(ph-py)(PCy3)2 (1) was prepared by adding 1 equiv of 2-phenylpyridine to RuH2(H2)2(PCy3)2. The ortho-metalated X ligand is coordinated to ruthenium via the nitrogen of one ring and the ortho carbon of a second ring as a result of C−H activation. 2 and 3 were characterized by X-ray diffraction. They are the first examples of complexes displaying exchange couplings between the hydride and the dihydrogen ligands. NMR studies and DFT calculations are used to understand this phenomenon. The series of ortho-metalated model complexes RuH(H2)(X)(PH3)2 was investigated by DFT at the B3PW91 level. The coherent (quantum-mechanical) as well as the incoherent (classical) exchange rates have been determined by line shape analysis, and the activation energies hardly depend on the nature of the X ligand:  Ea(coherent) = ca. 10 kJ mol^-1, Ea(incoherent) = ca. 40 kJ mol^-1 (ca. 50 kJ mol^-1 by DFT). The corresponding transition states (2q^TSQEC−4q^TSQEC) for the classical exchange process have been located by DFT at the B3PW91 level. The dihydrogen ligand is now trans to N and perpendicular to the plane of the chelating ligand. These states connect to the isomer with the dihydrogen trans to C through coupled rotation of H2 and proton transfer from H2 to H. The dihydrogen ligand can be substituted easily, and the corresponding complexes RuH(L)(ph-py)(PⁱPr3)2 with L = N2 (5), O2 (6), CO (7), C2H4 (8) have been isolated and fully characterized by NMR and by crystal structure analyses in the case of 6 and 8. The model systems RuH(L)(ph-py)(PH3)2 (5q−8q) have been optimized at the DFT level (B3PW91). In the case of 8, we could not detect any ethylene insertion in either the Ru−H or the Ru−C bond. Theoretical calculations explain the differences we observed with the Murai type catalysts, which are highly reactive to ethylene insertion.

Room-temperature stoichiometric reaction of the bis(dihydrogen) complex [RuH2(η²-H2)2(PCy3)2] (1) with thiophene leads to the formation of a new complex that has been isolated and characterized as an η⁴-thioallyl complex [RuH(η⁴(S,C)-SC4H5)(PCy3)2] (2). This complex easily regenerates 1 upon treatment with dihydrogen and can be successfully used as a catalyst precursor in thiophene hydrogenation to 2,3,4,5-tetrahydrothiophene (THT). The reaction of 1 with 2-acetylthiophene leads to a regioselective 1,5-C−S bond splitting with formal hydrogenation of two double C&dbd;C bonds and coordination of a new 2-hexen-2-olato-3-thiolato ligand in an η²(O,S) mode to form [RuH2{η²(O,S)-C6H10OS}(PCy3)2] (3). The new complex 3 has been characterized by ¹H, ³¹P, and ¹³C NMR studies including ¹H DPFGSE TOCSY, 2D-¹H−¹H{³¹P} COSY DQF, and the correlated ¹³C−¹H HMQC LR spectra. The solid state molecular structure of 3 has been unequivocally determined by single-crystal X-ray structure analysis. The bis(dihydrogen) complex 1 is an effective catalyst precursor for the homogeneous hydrogenation of thiophene (T) to 2,3,4,5-tetrahydrothiophene (THT), 2-methylthiophene (2-MeT) to 2-methyltetrahydrothiophene (2-MeTHT), 2-acetylthiophene (2-AcT) to 1-(2-thienyl)ethanol (1-(2-Tyl)E), 2-thiophenecarboxaldehyde (2-TA) to 2-thiophenemethanol (2-TM), and benzo[b]thiophene (BT) to 2,3-dihydrobenzo[b]thiophene (DHBT) under mild conditions (80 °C, 3 bar H2). Dibenzo[b,d]thiophene (DBT) is not reduced under these conditions due to the formation of the S-coordinated dihydrogen complex [RuH2(η²-H2){η¹(S)-C12H8S}(PCy3)2] (4).

Using a two-step procedure based on (i) anchoring an organogold precursor within the channels of functionalized ordered mesoporous silica containing mercapto groups; (ii) followed by chemical reduction, we prepared materials containing gold (0) nanoparticles exclusively located within the pore channels. By modifying the organogold precursor/mercapto groups ratio, we demonstrate the necessity of the complexation of the organogold precursor prior to reduction. Using this methodology, gold content as high as 16.1 wt % with a narrow size distribution of nanoparticles regularly distributed within the pores of the material was achieved.

The reaction of pyridine (Py), pyrrole (Pyr), or acridine with the bis(dihydrogen) complex [RuH2(η²-H2)2(PCy3)2] (1) produces compounds containing heteroaromatic ([RuH2(η²-H2)(η¹(N)-C5H5N)(PCy3)2] (2), [RuH(η⁵-C4H4N)(PCy3)2]·Pyr (3)) or aromatic rings ([RuH2(η⁴-C13H9N)(PCy3)2] (5)) coordinated in η¹(N) (2), η⁵(N,C) (3), or η⁴(C,C) (5) modes for Py, Pyr, and acridine, respectively. Complex 3 has been characterized by X-ray crystallography. Its protonation by HBF4 affords the cationic dihydride complex [RuH2(η⁵-C4H4N)(PCy3)2][BF4] (4). The coordinated Py ligand in 2 and acridine in 5 can readily be displaced by dihydrogen, with regeneration of 1. Regioselective hydrogenation of representative polynuclear heteroaromatic nitrogen compounds is achieved in the presence of 1 under mild reaction conditions (80 °C, 3 bar of H2). Quinoline (Q) and isoquinoline (iQ) are hydrogenated to 5,6,7,8-tetrahydro derivatives, while acridine is quickly reduced to 1,2,3,4-tetrahydroacridine followed by much slower saturation to 1,2,3,4,5,6,7,8-octahydroacridine (8H-Acr), the nitrogen-containing aromatic ring remaining intact. 8H-Acr has been isolated in analytically pure form and characterized by ¹H and ¹³C NMR as well as by X-ray crystallography. 5 is also active for catalytic acridine hydrogenation and can be regarded as an intermediate in the catalytic cycle. Saturation of a five-membered indole ring proceeds much slower than hydrogenation of six-membered aromatic rings in Q and iQ. Pyridine, pyrrole, and 7,8-benzoquinoline are not hydrogenated under the applied reaction conditions, as a result of the formation of new stable complexes.

NMR studies and DFT calculations (B3LYP) are used to elucidate the mechanisms for the hydride/(η²-Si-H) hydrogen exchange observed in the bis(silane) complexes RuH2[(η²-HSiMe2)2(CH2)2](PCy3)2 (2) and RuH2[(η²-HSiPh2)2O](PCy3)2 (4) obtained from the reactions of the bis(dihydrogen) ruthenium complex RuH2(H2)2(PCy3)2 (1) with the corresponding disilane HMe2Si(CH2)2SiMe2H or disiloxane HSiPh2OSiPh2H. Evidence is presented that exchange in 2 occurs via formation of isomers with dihydrogen ligands. Conversion of the most stable isomer A with C2v symmetry to the asymmetric Ru(η²-SiH)2 isomer B is the prelude to formation of the Ru(η²-SiH)(η²-H2) isomer C and the Ru(η²-H2)2 isomer D. Exchange occurs via rotation of the dihydrogen ligands and reversal of the isomerization process. The transformation of A into B via TSAB is the most energetically demanding individual step. This corresponds to the breaking of the SISHA (secondary interactions between silicon and hydrogen atoms) interactions between the silicons and the classical hydrides Hb and Hc. The calculated barrier of 43 kJ/mol for the complex with H3SiCH2CH2SiH3 and PH3 ligands compares to the experimental enthalpy of activation of 77 ± 11 kJ/mol for 2. Whereas complex 2 adopts a geometry with C2v symmetry, low-temperature NMR spectroscopy shows that complex 4 is present as two isomers, an asymmetric isomer with C1 symmetry and the symmetric isomer in proportions of ca. 1:2. The pathways for interconversion of the isomers and for exchange between the hydride and SiH hydrogen atoms have been delineated by DFT calculations and resemble those for complex 2. Reaction of 4 with excess triphenylphosphine yields RuH2{(η²-H-SiPh2)O(SiHPh2)}(PPh3)3 (5), which is shown by NMR spectroscopy to contain one coordinated and one uncoordinated SiH group. A crystal structure of the partially hydrolyzed analogue RuH2{(η²-H-SiPh2)O(Si(OH)Ph2)}(PPh3)3 (6) confirms the assignment. A ruthenium(II) formulation with one (η²-SiH) bond and two SISHA interactions is favored over a ruthenium(IV) structure with three hydrides and a silyl ligand.

Reaction of the bis(dihydrogen)ruthenium complex RuH2(H2)2(PCy3)2 (1) with 1 equiv of the dicationic heterocyclic carbene precursor (C6H13N3)(SO3CF3)2 (3) produces in good yield the hydrido carbene complex [RuH(C6H12N3)(OSO2CF3)(PCy3)2][SO3CF3] (4). An X-ray structural analysis of 4 confirms the triflate coordination to the metal. NMR data show that, in solution, 4 exists as a mixture of two isomers. By addition of 1 equiv of the dicationic carbene precursor 3 to the dimer [Cp*Ru(μ-OMe)]2 (2), the tricationic bis(carbene) complex [Cp*Ru(C6H12N3)2][SO3CF3]3 (7) is isolated in moderate yield and has been characterized by an X-ray structural determination and NMR data.

Nickel nanoparticles of tunable shape have been synthesized in THF, in the presence of hexadecylamine (HDA) or trioctylphosphineoxide (TOPO), in mild conditions and characterized by HREM and SQUID measurements. The formation of nanorods is promoted by a high amine content in the reaction medium. In contrast to what is observed for TOPO-protected nickel particles, the saturation magnetization of HDA-capped nanoparticles is comparable to that of bulk nickel, which demonstrates that the coordination of an amine ligand does not alter the magnetic properties of nickel.

The bis(dihydrogen) ruthenium complex RuH2(H2)2(PCy3)2 (1) and the ethylene complex RuΗ(C2Η4)[P(η³-C6H8)Cy2](PCy3) (2), obtained by addition of ethylene to 1, catalyze efficiently the silylation of ethylene with HSiMe2SiMe2H (I) and with the series of disilanes HSiMe2(CH2)nSiMe2H (n = 2, II; n = 3, III; n = 4, IV). Reaction of I with ethylene produces the monosilanes (CH2&dbd;CH)SiMe2(CH2CH3) (I.b) and (CH3CH2)SiMe2(CH2CH3) (I.c) resulting from the cleavage of the Si−Si bond and the functionalization of the Si−H bonds. For II−IV, three processes, hydrosilylation, dehydrogenative silylation, and cyclization, are in competition, leading to the formation of acyclic monofunctionalized intermediates HSiMe2(CH2)nSiMe2(CH&dbd;CH2) (II.f−IV.f) and HSiMe2(CH2)nSiMe2(CH2CH3) (II.g−IV.g), acyclic difunctionalized compounds (CH2&dbd;CH)SiMe2(CH2)nSiMe2(CH&dbd;CH2) (II.a−IV.a), (CH2&dbd;CH)SiMe2(CH2)nSiMe2(CH2CH3) (II.b−IV.b), and (CH2CH3)SiMe2(CH2)nSiMe2(CH2CH3) (II.c−IV.c), together with cyclic products [(SiMe2)(CH2)3(SiMe2)](CH&dbd;CH2) (II.d−IV.d) and [(SiMe2)(CH2)3(SiMe2)](CH2CH3) (II.e−IV.e). Kinetic studies reveal a consecutive reaction path for the formation of acyclic difunctionalized compounds via the monofunctionalized intermediates. Saturated and unsaturated cyclic products form concurrently to monofunctionalized disilanes. The rates and the selectivity of the reactions are dramatically influenced by the chain length between the two silicon atoms, the fastest conversion and the highest concentration of vinyl products being observed in the case of a long chain. In contrast, formation of cyclic compounds is favored for n = 2 or 3. Mechanistic studies show that different complexes are obtained, depending on the order of addition of ethylene and disilane. In the presence of the disilane II, 2 converts into a mixture of RuH2{(η²-HSiMe2)2(CH2)2}(PCy3)2 (3a) and RuH2(SiMe2(CH2)2SiMe2H){P(η³-C6H8)Cy2}(PCy3) (6). In contrast, in the presence of ethylene, RuH2{(η²-HSiMe2)2(CH2)n}(PCy3)2 (n = 2, 3a; n = 3, 3b), leads to the formation of a new ethylene complex RuH2(C2H4)2(PCy3)2 (4). Compound 4 is ultimately converted to 2 after total consumption of the liberated disilane. All these complexes are involved in the catalytic processes.

Ruthenium complexes containing the dihydridobis(3,5-bis(trifluromethyl)pyrazolyl)borate ligand Bp^(CF3)2 have been prepared and structurally characterized. Reaction of (Bp^(CF3)2)RuH(COD) (1a) with 2 equiv of bulky phosphines PR3 under 3 bar of H2 produces the hydrido(dihydrogen) complexes (Bp^(CF3)2)RuH(H2)(PR3)2 (R = Cy, 2a; R = ⁱPr, 3a). X-ray structural analysis of 3a confirms a κ² N,H bonding mode of the Bp^(CF3)2 ligand. In the absence of dihydrogen, the monohydride complex (Bp^(CF3)2)RuH(COD)(PCy3) (4a) is isolated. Upon pressurization to 3 bar H2, 4a converts into (Bp^(CF3)2)RuH(H2)(PCy3) (5a) with rechelation of the pendant pyrazolyl ring and hydrogenation of the COD ligand. Addition of 2 equiv of PPh3 or Ppyl3 to 1a under 3 bar of H2 leads to the formation of the corresponding hydrido complexes (Bp^(CF3)2)RuH(PR3)2 (R = Ph, 6a; R = pyl, 7a). Under similar conditions, 1a reacts with 2 equiv of ^tBuNH2 to produce the amine adduct (Bp^(CF3)2)RuH(^tBuNH2)2 (8a). By addition of 1 equiv of MeI to 8a, the iodo complex (Bp^(CF3)2)RuI(^tBuNH2)2 (9a) is isolated and characterized by an X-ray structural determination. The analogous chloro complex (Bp^(CF3)2)RuCl(^tBuNH2)2 (10a) can be prepared by stirring a dichloromethane solution of 8a for 18 h. In the absence of dihydrogen, 1a reacts with a large excess of ^tBuNH2 to give (Bp^(CF3)2)RuH(COD)(^tBuNH2) (11a). The structure with a κ² N,H coordination of the Bp^(CF3)2 ligand is confirmed by an X-ray determination. Using the more sterically demanding diisopropylamine in the same conditions used for the formation of 8a, we could not isolate any complex. However upon N2 atmosphere, the dinuclear species with a μ²-bridging dinitrogen ligand [(Bp^(CF3)2)RuH(ⁱPr2NH)]2(N2) (12a) could be isolated and characterized by a single-crystal X-ray determination. Addition of mesitylene to 1a produces the arene complex (Bp^(CF3)2)RuH(η⁶-C6H3Me3) (13a). The X-ray structure determination gave conclusive evidence for the κ² N,N bonding mode of the Bp^(CF3)2 ligand. When exposing 1a to a CO atmosphere, the new acyl(dicarbonyl) complex (Bp^(CF3)2)Ru(COC8H13)(CO)2 (14a) is isolated in very high yield. Its structure is fully characterized on the basis of 2D homonuclear and heteronuclear correlation NMR data and by an X-ray structural determination. Similar reactions have been performed using the nonfluorinated complex (Bp^Me2)RuH(COD) (1b) as starting material. The analogous complexes 2b, 4b−6b, and 14b have been obtained. The variation of of the hapticity of the Bp ligand plays a crucial role in this chemistry, but the fluorinated substituents have a limited influence.

The reaction of Co(η3-C8H13)(η4-C8H12) and Pt2(dba)3 (dba = bis-dibenzylidene acetone) under dihydrogen leads in the presence of poly(vinylpyrrolidone) to nanometric bimetallic particles CoxPt1-x. The composition of the material is determined by the initial ratio of the two organometallic precursors. The bimetallic character of the particles is evidenced by magnetic, structural, and spectroscopic studies. Structural changes are evidenced both by HREM and WAXS:  platinum rich particles adopt a fcc crystalline structure while cobalt rich particles adopt a non periodic polytetraedral arrangement. The magnetic properties of the materials have been investigated. ZFC/FC measurements show that the particles are superparamagnetic and that their size dispersity is very low. From isothermal magnetization measurements, the extrapolated value of the coercive field HC (T = 0) is shown to increase continuously with Pt concentration, which is characteristic of bimetallic particles.

Very small nanometric oxide particles (CoO and Co3O4, around 2 nm in diameter) well dispersed inside a polymer matrix were prepared by solid-state oxidation of a metallic colloid precursor (1.6 nm Co particles). WAXS (wide-angle X-ray scattering) and HREM (high-resolution electronic microscopy) were used to observe very precisely the structural changes occurring during the oxidation process. With cobalt particles a few nanometers large, air oxidation at room temperature results in a surface passivation. Consequently the particles show a composite structure with a metallic core surrounded by an oxide surface layer. Preliminary magnetic measurements reveal that unidirectional exchange anisotropy between the metallic ferromagnetic core and the antiferromagnetic oxide layer occurs below 130 K.

A new ruthenium hydride complex of the aminocyclopentadienyl ligand (Cp-N)RuH(PPh3)2 (Cp-N = C5H4CH2CH2NMe2, 1) has been prepared and characterized by X-ray diffraction. Protonation of 1 with excess HPF6 leads to the dicationic derivative [(Cp-NH)RuH2(PPh3)2](PF6)2 (2), in which both the metal and the amino substituent have been protonated. Addition of 1 equiv of HBF4·Et2O to 1 leads to the complex [(Cp-N)Ru(PPh3)2](BF4) (3), containing a chelating amino cyclopentadienyl ligand after elimination of H2. However, using (HNEt3)(BPh4) or (HPBu3)(BPh4) as protonating agent, it is possible to form [(Cp-NH)RuH(PPh3)2](BPh4) (4), which was isolated as yellow crystals of 4·H2O upon addition of undistilled methanol and characterized by X-ray crystallographic analysis. A fluxional process exchanging the ammonium proton and the hydride without changing the thermodynamic state of the system could be established by ¹H NMR, and activation energies of 11 kcal·mol^-1 were calculated for 4·H2O and the product resulting from in situ addition of [HNEt3][BPh4] to 1, whereas an activation energy of 10.1 kcal·mol^-1 was found for the product resulting from in situ addition of [HPBu3][BPh4] to 1. A density functional study (B3PW91) was carried out, and the dihydrogen bond in the model system for 4 was calculated to be 1.545 Å, in excellent agreement with T1 measurements (1.52 Å). The proposed mechanism for the fluxional process does not involve a proton transfer within the dihydrogen bond.

The reaction of Pt(dba)2 with Ru(COD)(COT) in various proportions under dihydrogen in the presence of PVP leads to the formation of bimetallic nanoparticles of definite compositions resulting from the relative concentration of the two complexes in the initial solution. The progressive incorporation of ruthenium into the platinum matrix leads to structural changes from face-centered cubic (fcc) for high platinum contents to hexagonal close-packed (hcp) for high ruthenium contents. For the composition Pt1Ru3 a contraction of the size of the particles (ca. 1.1 nm) and of the size distribution indicates the presence of a new phase consisting of monodisperse particles for which a model of truncated twinned octahedrons of 79 atoms was proposed.

New dendrimers 3-[G‘1]−3-[G‘4] possessing from 6 to 48 N(CH2PPh2)2 terminal groups are described. The corresponding Pd, Pt, and Rh complexes [N(CH2PPh2)2MRR‘]y (y from 6 to 24; generations 1−3) [M = Pd:  R = R‘ = Cl, Br; R = Cl, R‘ = Me; R = Br, R‘ = Me; R = Cl, R‘ = COMe; R = Cl, R‘ = norbornyl-COMe. M = Pt:  R = R‘ = Br, Cl, Me; R = Br, R‘ = Me. M = Rh:  R, R‘ = acac] are prepared by reacting 3-[G‘1]−3-[G‘3] with the appropriate transition metal complexes.

The reactivity of the ruthenium(IV) trihydride complex Cp*RuH3(Ppyl3) (2), accommodating the π-accepting tripyrrolylphosphine (Ppyl3), has been studied with regard to substitution and protonation reactions. Substitution of two hydrides by excess Ppyl3 and CO leads to Cp*RuHL(Ppyl3) (L = Ppyl3, 3; L = CO, 4). The reaction with ^tBuNC leads first to the substitution of two hydrides by the ligand, but the reaction proceeds further to yield, through an unprecedented decyanation reaction, the cyano complex Cp*Ru(CN)(^tBuNC)(Ppyl3) (6), which has been characterized by X-ray diffraction. Addition of HSiMe2Ph in refluxing toluene yields Cp*RuH2(SiMe2Ph)(Ppyl3) (7), a dihydridosilylruthenium(IV) complex that has been characterized by spectroscopic data and an X-ray crystal structure. Finally, protonation of 4 yields the dihydrogen complex [Cp^*Ru(H2)(CO)(Ppyl3)](BF4) (8), which easily loses H2 in solution and displays a very short T1 minimum, in agreement with a low electron density on the metal.

The reaction of the ruthenium polyhydrides RuH2(PPh3)4 and RuH2(H2)2(PCy3)2 with the previously reported dendrimers Gx-N(CH2PPh2)2 (first, second, and third generations; G1, G2, and G3) cleanly leads to the new complexes [Gx-N(CH2PPh2)2]RuH2(PPh3)2 (1-Gx) and [Gx-N(CH2PPh2)2]RuH2(H2)(PCy3), which exist as a mixture of isomers (3‘-Gx, 3‘‘-Gx, 4‘-Gx, and 4‘‘-Gx). Complexes 3-Gx/4-Gx were shown to accommodate a stretched dihydrogen ligand and to display a high temperature for the minimum of the T1 relaxation time, in agreement with their binding to the dendrimer in solution. The reactivity of these complexes with CO, leading to new dihydrido carbonyl ruthenium complexes (2-Gx, 5-Gx), is described.

Treatment of RuH2(H2)2(PCy3)2 (1) with ethylene leads to the formation of [RuH{η³-C6H8)PCy2}(C2H4)(PCy3)] (2), which contains an η³-cyclohexenyl ring. Upon addition of 3 equiv of an alkene bearing σ-donor substituents such as CH2&dbd;CH(SiEt3) or CH2&dbd;CH^tBu, 1 transforms in high yield into the trihydridoruthenium(IV) complex [RuH3{(η³-C6H8)PCy2}(PCy3)] (3) and the corresponding alkane is obtained quantitatively. Further hydrogen abstraction from 1 can be achieved by using 5 equiv of alkene, leading to the hydridoruthenium(II) complex [RuH{(η³-C6H8)PCy2}{(η²-C6H9)PCy2}] (4). This is the first complex where C−H activation within two cyclohexyl rings of two tricyclohexylphosphines has occurred. 4 can also be obtained by treatment of 3 with 2 equiv of alkene. The reactions can be reversed by bubbling dihydrogen into a solution of 2−4 yielding 1 at the final stage of hydrogenation. 3 and 4 undergo rapid H−D exchange with the deuterated solvent. Reaction of 1 with alkenes bearing electron-withdrawing substituents such as CH2&dbd;CHCO2Me or trans-MeO2CCH&dbd;CHCO2Me allows the formation of the hydrido dihydrogen complexes [RuH(H2)(η²-O2CCH2CH3)(PCy3)2] (5) and [RuH(H2)(η²-O2CCH2CH2CO2Me)(PCy3)2] (6), respectively. An X-ray structure determination on 5 was carried out. Surprisingly, reaction of 1 with cis-MeO2CCH&dbd;CHCO2Me yielded the alkene-coordinated complex [RuH2(η²-CH3O2CCH&dbd;CHCO2CH3)(PCy3)2] (7). Variable-temperature NMR studies on 7 showed a barrier of rotation for the alkene of 10.5 kcal/mol. 7 was shown to catalyze cis−trans MeO2CCH&dbd;CHCO2Me isomerization.

The reaction of Pt(dba)2 with CO (1 atm) in toluene affords a brown precipitate which can be isolated and redissolved in CH2Cl2 to give a colloidal solution of fcc platinum particles with a large size dispersity (10−20 Å, I). Redissolution of I in THF leads to stable 12 Å fcc platinum particles (II) which can be isolated and characterized by high-resolution electron microscopy (HREM) and wide-angle X-ray scattering (WAXS). The original reaction in THF leads to the direct formation of II. Addition of 0.2 equiv of PPh3 to II yields a new colloid, III, of the same size but of icosahedral structure. III was characterized by HREM and spectroscopic techniques. In particular, ¹³C and ³¹P NMR spectroscopy demonstrates the absence of a Knight shift for these particles. Addition of excess triphenylphosphine leads to another species, IV, displaying broader size distribution with a maximum at 17 Å and an fcc structure. The reaction of I with more than 0.2 equiv of PPh3 affords mixtures containing colloids, clusters (predominantly Pt5(CO)6(PPh3)4), and mononuclear complexes. Both the formation of the colloids and their transformation into molecular species is rapid at room temperature. It is suggested that such processes may be more frequent in organometallic chemistry than previously thought.

Sonolysis of a solution of Fe(CO)5 in anisol in the presence of poly(dimethylphenylene oxide) (PPO) leads to the formation of small nonagglomerated iron particles. HREM analysis shows that the size of the particles is centered around 30 Å with a medium dispersity. HREM analysis of the particles demonstrate that the smaller particles (≤25 Å) adopt the α-Fe (bcc) structure, whereas the larger ones (≥25 Å) adopt the γ-Fe (fcc) structure. Magnetic measurements confirm the presence of small superparamagnetic particles (α-Fe) and of mostly antiferromagnetic or paramagnetic particles (γ-Fe).

Isomerization of 2-methyl-3-butenenitrile to 3-pentenenitrile is catalyzed by nickel π-allyl cyanide complexes. The mechanism is supported by in situ NMR monitoring and DFT studies.