Complex RuH Research Articles

Dimethylaminoborane (H2BNMe2) Coordination to Late Transition Metal Centers: Snapshots of the B–H Oxidative Addition Process.

The reaction of cyclodiborazane [Me(2)N-BH(2)](2) with the chloro(dihydrogen) ruthenium complex RuHCl(η(2)-H(2))(P(i)Pr(3))(2) (1) led to the formation of the unsymmetricaly coordinated dimethylaminoborane complex RuHCl(H(2)BNMe(2))(P(i)Pr(3))(2) (2). The dimethylaminoborane coordination (H(2)BNMe(2)) to the ruthenium center in 2 was carefully studied by combining X-ray, multinuclear NMR, and density functional theory (DFT) techniques, and compared with the recently reported osmium analogue which was originally formulated as a σ-B-H borinium complex [OsH(2)Cl(HBNMe(2))(P(i)Pr(3))(2)] (4). All our data are in favor of a bis(σ-B-H) coordination mode at a very activated stage in the case of the ruthenium complex 2, whereas in the osmium complex 4, full oxidative addition is favored leading to a complex better formulated as an osmium(IV) boryl species with an α-agostic B-H interaction. The synthesis and characterization of the symmetrical dihydride complex RuH(2)(H(2)BNMe(2))(P(i)Pr(3))(2) (3) from addition of the lithium dimethylaminoborohydride to 1 is reported for comparison.

Ruthenium-Catalyzed (2 + 2) Intramolecular Cycloaddition of Allenenes

We report a ruthenium-catalyzed (2 + 2) intramolecular cycloaddition of allenes and alkenes. We have found that the use of the ruthenium complex RuH(2)Cl(2)(P(i)Pr(3))(2), which has previously gone unnoticed in catalytic applications, is crucial for the observed reactivity. The reaction proceeds under mild conditions and is fully diastereoselective, providing a practical entry to a variety of bicyclo[3.2.0]heptane skeletons featuring cyclobutane rings.

Tridentate and Tetradentate Iminophosphorane-Based Ruthenium Complexes in Catalytic Transfer Hydrogenation of Ketones

Tetradentate iminophosphorane complexes [RuH(PNNP)][BArF4] (5) and [RuHCl(PNNP)] (6) (PNNP = PPh2CH2PPh2NCH2CH2NPPh2CH2PPh2), prepared by in situ deprotonation of the aminophosphonium ligands in the presence of the dihydrogen complex RuH(H2)(Cl)(PCy3)2, are active precatalysts for the catalytic transfer hydrogenation of ketones at 80 °C under basic conditions in HOiPr. Complex 6 was characterized by X-ray diffraction. With a predominant focus on acetophenone, a comparative study with [RuH(H2NNPP)(PCy3)][BArF4] (3) incorporating a tridentate ligand (H2NNPP = H2N(C6H4)NPPh2CH2PPh2) does not indicate an NH effect. It is postulated that the pentacoordinated configuration around Ru with a hydride trans to a vacant site is essential in the catalyst resting state; however, the stability of this structural arrangement is disadvantageous for high activities. Further mechanistic studies, including labeling experiments, indicate facile protonation of these systems and, in addition, structural variations as a function of protonating agent (HOiPr, HX, H2O). The hydrido(chloro) complex RuH(Cl)(HNP)(NP) (7) (NP = Ph2PCH2PPh2NCH2tBu) was also isolated and characterized by X-ray diffraction, and a hydrogen bond between the chlorine and the NH group of the pendant ligand was ascertained by DFT calculations.

From amine to ruthenaziridine to azaallyl: unusual transformation of di-(2-pyridylmethyl)amine on ruthenium

The complexation of di-(2-pyridylmethyl)amine to RuHCl(PPh(3))(3) affords the salt [RuH{κ(3)N-fac-1,3-di-(2-pyridylmethyl)amine}(PPh(3))(2)]Cl. Reaction with potassium tert-butoxide at room temperature yields the unusual ruthenaziridine complex RuH{κ(3)C(alk)NN(py)-1,3-di-(2-pyridylmethyl)amine}(PPh(3))(2), where the central nitrogen atom, adjacent alkyl carbon, and pyridine arm coordinate to the metal, leaving the second pyridine arm uncoordinated. Surprisingly, heating of this ruthenaziridine complex with concomitant H(2) formation affords the ruthenium azaallyl complex RuH(κ(3)N-1,3-di-(2-pyridyl)-2-azaallyl)(PPh(3))(2). This is a rare example of a 4d metal complex containing the azaallyl ligand. X-Ray crystal structures and NMR characterization of all three compounds are presented herein.

Ruthenium-Catalyzed Hydrogenation of Nitriles: Insights into the Mechanism

Hydrogenation of benzonitrile into benzylamine is catalyzed under very mild conditions by the ruthenium bis(dihydrogen) complex RuH(2)(H(2))(2)(PCyp(3))(2), incorporating two tricyclopentylphosphines. Two key intermediates have been isolated, resulting from the activation of benzonitrile at early stages of activation, i.e., either N-coordination through the nitrile function or first hydrogenation with benzylimine formation, followed by, thanks to C-H activation, coordination at ruthenium as an orthometalated ligand.

Silyl and σ-silane ruthenium complexes: Chloride substituent effects on the catalysed silylation of ethylene

Silylation of ethylene by the chlorosilanes HSiMe(2)Cl and HSiMeCl(2) was catalysed by the bis(dihydrogen) complex RuH(2)(eta(2)-H(2))(2)(PCy(3))(2) (1). Dehydrogenative silylation leading to the formation of the corresponding vinylsilanes was in competition with hydrosilylation. The rate and selectivity of the reactions were influenced by the number of chloro substituents and the ethylene pressure. A comparative mechanistic study was performed in toluene-d(8) with the two chlorosilanes. Reaction of 1 with an excess of HSiMe(2)Cl (10 equiv.) produced the sigma-silane complexes RuH(2)(eta(2)-H(2))(eta(2)-HSiMe(2)Cl)(PCy(3))(2) (2Me(2)Cl), RuH(2)(eta(2)-HSiMe(2)Cl)(2)(PCy(3))(2) (3Me(2)Cl) and the silyl complex RuCl(SiMe(2)Cl)(eta(2)-H(2))(PCy(3))(2) (4Me(2)Cl), all characterised by multinuclear NMR spectroscopy. Complexes 2Me(2)Cl and 3Me(2)Cl adopt a cis configuration for the two bulky phosphine ligands as a result of stabilising SISHA (Secondary Interactions between Silicon and Hydrogen Atoms) interactions. Complex 4Me(2)Cl resulted from the stoichiometric reaction of HSiMe(2)Cl with 1 producing RuHCl(eta(2)-H(2))(PCy(3))(2)in situ which further reacted with evolution of H(2) and formation of 4Me(2)Cl. When reacting 1 with 10 equiv. of HSiMeCl(2), the corresponding complexes 3MeCl(2) and 4MeCl(2) were detected as well as traces of 2MeCl(2). The reactivity toward ethylene was then examined. Under catalytic conditions (excess silane in toluene-d(8), ethylene atmosphere) only two compounds could be characterised: free PCy(3) and the new (eta(6)-aryl)(disilyl) complexes of the general formula Ru(eta(6)-C(6)D(5)CD(3))(SiMe(3-n)Cl(n))(2)(PCy(3)) (6Me(3-n)Cl(n)-d(8), n = 1,2). The X-ray structure of 6MeCl(2) was obtained on a single-crystal at 160 K. When only 2 equiv. of HSiMe(2)Cl were added, the ethylene(silyl) complex RuH(SiMe(2)Cl)(C(2)H(4))(PCy(3))(2) (7Me(2)Cl) was obtained in addition to the organic products resulting from catalytic hydrogenation, hydrosilylation and dehydrogenative silylation, i.e. C(2)H(6) (major one), C(2)H(3)SiMe(2)Cl and C(2)H(5)SiMe(2)Cl. In the case of 2 equiv. of HSiMeCl(2), upon ethylene addition, 7MeCl(2) was formed in minority compared to a new disilyl complex Ru(SiMeCl(2))(2)(PCy(3))(2) (8MeCl(2)) characterised by NMR spectroscopy and X-ray diffraction on a single crystal at 160 K. In 8MeCl(2), a formal 14-electron species, stabilisation through two agostic C-H bonds of the cyclohexyl groups was ascertained by DFT calculations.

Ruthenium(II) Complex Catalyzed O-Borylation of Alcohols with Vinylboronates

A new, highly effective method for the selective synthesis of boryl ethers via O-borylation of alcohols with vinylboronates catalyzed by the Ru-H complexes [Ru(CO)C]H(PPh 3 ) 3 ] and [Ru(CO)CIH(PC Y3 ) 2 ] is described. The mechanism of catalysis of this new de-ethenative borylation is supported by equimolar reaction of Ru-B complex with alcohol.

Versatile Coordination of 2-Pyridinetetramethyldisilazane at Ruthenium: Ru(II) vs Ru(IV) As Evidenced by NMR, X-ray, Neutron, and DFT Studies

The novel disilazane compound 2-pyridinetetramethyldisilazane (1) has been synthesized. The competition between N-pyridine coordination and Si-H bond activation was studied through its reactivity with two ruthenium complexes. The reaction between 1 and RuH(2)(H(2))(2)(PCy(3))(2) led to the isolation of the new complex RuH(2){(eta(2)-HSiMe(2))N(kappaN-C(5)H(4)N)(SiMe(2)H)}(PCy(3))(2) (2) resulting from the loss of two dihydrogen ligands and coordination of 1 to the ruthenium center via a kappa(2)N,(eta(2)-Si-H) mode. Complex 2 has been characterized by multinuclear NMR experiments ((1)H, (31)P, (13)C, (29)Si), X-ray diffraction and DFT studies. In particular, the HMBC (29)Si-(1)H spectrum supports the presence of two different silicon environments: one Si-H bond is dangling, whereas the other one is eta(2)-coordinated to the ruthenium with a J(SiH) value of 50 Hz. DFT calculations (B3PW91) were also carried out to evaluate the stability of the agostic species versus a formulation corresponding to a bis(sigma-Si-H) isomer and confirmed that N-coordination overcomes any stabilization that could be gained by the establishment of SISHA interactions. There is no exchange between the two Si-H bonds present in 2, as demonstrated by deuterium-labeling experiments. Heating 2 at 70 degrees C under vacuum for 24 h, leads to the formal loss of one equivalent of H(2) from 2 and formation of the 16-electron complex RuH{(SiMe(2))N(kappaN-C(5)H(4)N)(SiMe(2)H)}(PCy(3))(2) (3) formulated as a hydrido(silyl) species on the basis of multinuclear NMR experiments. The dehydrogenation reaction is fully reversible under dihydrogen atmosphere. Reaction of Ru(COD)(COT) with 3 equiv of 1 under a H(2) pressure led to the isolation of the new complex RuH{(SiMe(2))N(kappaN-C(5)H(4)N)(SiMe(2)H)}(3) (4) characterized as a hydridotrisilyl complex by multinuclear NMR techniques, X-ray and neutron diffractions, as well as DFT calculations. The (29)Si HMBC experiments confirm the presence of two different silicon atoms in 4, with a signal at -14.64 ppm for three dangling Si-Me(2)H fragments and a signal at 64.94 ppm (correlating with the hydride signal) assigned to three Si-Me(2)N groups bound to Ru. Comparison of DFT and neutron parameters involving the hydride clearly indicates an excellent correlation. The Si-H distance of approximately 2.15 A is much shorter than the sum of the van der Waals radii and typically in the range of a significant interaction between a silicon and a hydrogen atom (SISHA interactions). In 4, three dangling Si-H groups remain accessible for further functionalization.

Tert-butylborane: A bis (σ-B–H) ligand in ruthenium hydride chemistry

The reaction of tert-butylborane with the bis(dihydrogen) complex RuH 2(η 2-H 2) 2(PCy 3) 2 leads to the corresponding bis σ-borane complex which is the first example of a monoalkylborane ruthenium bis σ-complex. An alternative route involves the reaction of RuHCl(η 2-H 2)(PCy 3) 2 with lithium tert-butylborohydride.

Synthesis and electrochemical properties of bimetallic η5-indenyl ruthenium complexes

Treatment of RuCl(dppm)(η5-C9H7) with alkynes HC≡C(C6H4)nC≡CH (n = 1, 2) in the presence of TlPF6 and t-BuONa affords the bimetallic ruthenium acetylide complexes [(η5-C9H7)(dppm)Ru]2(µ-C≡C(C6H4)nC≡C). Reactions of the hydride complex RuH(dppm)(η5-C9H7) with HC≡C(C6H4)nC≡CH (n = 1, 2) in refluxing toluene give the bimetallic ruthenium alkenyl complexes [(η5-C9H7)(dppm)Ru]2(µ-CH=CH(C6H4)nCH=CH). The electrochemical properties of the new complexes have been investigated by cyclic voltammetry, which reveals that the organic spacer –CH=CHC6H4CH=CH– is more effective than –C≡CC6H4C≡C– in mediating electronic communication between the two ruthenium moieties.Key words: ruthenium, bimetallic, acetylide, insertion, electrochemistry.

Access to Ruthenium(0) Carbonyl Complexes via Dehydrogenation of a Tricyclopentylphosphine Ligand and Decarbonylation of Alcohols

The carbonylruthenium(0) complex Ru(CO){PCyp2(η2-C5H7)}2 (4) has been prepared by reaction of RuH2{PCyp2(η2-C5H7)}2 (3) with an excess of tert-butylethylene in the presence of ethanol. Decarbonylation of ethanol is also observed when reacting the bis(dihydrogen) complex RuH2(η2-H2)2(PCyp3)2 (1) with 2 equiv of ethanol. The reaction results formally in the substitution of one dihydrogen ligand by a carbonyl, and the corresponding complex RuH2(η2-H2)(CO)(PCyp3)2 (5) was isolated. An excess of tert-butylethylene reacted with 5 to give RuH2(CO){PCyp2(η2-C5H7)}(PCyp3) (6), which corresponds to the formal loss of 2 equiv of dihydrogen: loss of the dihydrogen ligand and dehydrogenation of one cyclopentyl ring. The dihydride 6 can be dehydrogenated further by reaction with ethylene, affording the ruthenium(0) complex Ru(η2-C2H4)(CO){PCyp2(η2-C5H7)}(PCyp3) (7). Finally, the dicarbonyl complex RuH2(CO)2(PCyp3)2 (8) was isolated by exposing 1 to 3 bar of CO. 8 and the new complexes 4−7, resulting from partial dehydrogenation of one or two cyclopentyl rings of the tricyclopentylphosphines and/or decarbonylation of alcohol, were characterized by multinuclear NMR, IR, elemental analysis, and X-ray diffraction.

Quantum chemical investigations of intramolecular isomerization in RuH 2(CO) 2(PMe 3) 2

The coordination of CO to the ruthenium complex RuH 2(PCy 3) 2 has been investigated by means of the DFT/B3LYP method. The modeling of PCy 3 by PMe 3 fits better with the experimental results than phosphine PH 3. Several isomers have been calculated on the potential energy surface and the three lowest isomers were found to have very similar energies in perfect agreement with experimental results. The most stable isomer presents the phosphines in trans position while the two carbonyl ligands are in cis position. The isomerization process between the two most stable isomers has been studied. The value of the isomerization barrier is 113.5 kJ mol −1. The thermodynamic analysis of CO and H 2 bonding indicates a strong interaction between the carbonyl ligand and the metallic center. The good catalytic activity of this compound may be interpreted in terms of the great facility of dihydrogen molecules to be replaced by carbonyls.

Hydrogenation of Benzonitrile to Benzylamine Catalyzed by Ruthenium Hydride Complexes with P−NH−NH−P Tetradentate Ligands: Evidence for a Hydridic−Protonic Outer Sphere Mechanism

The reaction of RuHCl(PPh3)3 with the tetradentate ligand [PPh2((ortho-C6H4)CH2NHCH2-)]2 {ethP2(NH)2} in THF produces the new complex trans-RuHCl{ethP2(NH)2} (1) as a mixture of two isomers. The complex RuHCl{ethP2(NH)2} (1) when activated with KOtBu/KH is a very active catalyst for the hydrogenation of benzonitrile to benzylamine in toluene, more active than the known catalyst Ru(H2)2H2(PCy3)2 (2). A mixture of 1 and 2 and base also results in efficient conversion of benzonitrile to benzylamine. The complex RuHCl{tmeP2(NH)2} (3) where tmeP2(NH)2 is [PPh2((ortho-C6H4)CH2NHCMe2-)]2 is a less active catalyst for this reaction. These catalyst systems are air sensitive and extremely moisture sensitive. Experimental and theoretical (DFT) evidence is presented for a new mechanism for nitrile hydrogenation: the successive hydrogenation of the CN triple bond and then the CN double bond of the intermediate imine by H+/H- transfer from a trans dihydride active catalyst. The amido complex RuH{tmeP2N(NH)} (4) has si...

A Mechanism Displaying Autocatalysis: The Hydrogenation of Acetophenone Catalyzed by RuH(S-binap)(app) Where app Is the Amido Ligand Derived from 2-Amino-2-(2-pyridyl)propane

The 2-(aminomethyl)pyridine (ampy) ligand is known to activate ruthenium complexes for the catalytic hydrogenation of ketones. Here we prepare well-defined catalysts using the new ligand 2-amino-2-(2-pyridyl)propane (appH) in order to elucidate the role of the pyridyl group. The ligand has two methyl groups on the α-carbon to block β-hydride elimination reactions. It reacts with RuHCl(S-binap)(PPh3) to produce the orange-yellow complex RuHCl(S-binap)(appH) (2). In the presence of a strong base (KOtBu), complex 2 is converted into an active catalyst for the H2-hydrogenation of acetophenone in benzene under mild conditions (20 °C, 5 atm H2). Solutions of 2 rapidly react with KOtBu under an argon atmosphere to produce a deep red amidohydrido complex RuH(S-binap)(app) (3), which is an active catalyst. A crystal structure determination of 3 represents the first structure of a Ru-binap hydrido-amido complex. It reveals a five-coordinate Ru(II) center with a short Ru−N(amido) distance (1.962(3) Å) and a trigonal planar geometry at the amido nitrogen. The kinetic experiments using 3 as a catalyst and acetophenone as a substrate in benzene show that the rate of 1-phenylethanol production is dependent on both catalyst and H2 concentrations. These results parallel the behavior of the conventional Noyori-type Ru(II) catalysts with diamine ligands. However, unique features of catalysis with 3 are as follows: (1) the formation of a dihydride is thermodynamically unfavorable at 1 atm H2, 20 °C; (2) the rate shows a dependence on the product concentration since it increases as the product builds up during the reaction in an autocatalytic fashion. A significant increase in the initial rate is observed when a critical concentration of rac-1-phenylethanol is present at the beginning of the reaction. The addition of 2-propanol in benzene raises the rate as well, and the fastest H2-hydrogenation is achieved if 2-propanol is used as a solvent. This “alcohol effect” is favored by the pyridyl ligand app since it was not observed for the similar catalyst RuH(NHCMe2CMe2NH2)(binap). While 3 is an exceptional catalyst for H2-hydrogenation in 2-propanol (TOF > 6700 h-1 at 20 °C, 5 atm H2), it has a lower activity in transfer hydrogenation from the same solvent under comparable conditions (TOF 110 h-1 at 20 °C, 1 atm Ar). DFT calculations on the model amido complex Ru(H)(PH3)2(HNCH2C5H4N) (4) confirm that the splitting of H2 to give the trans dihydride is the turnover-limiting step and lies 9 kcal/mol in free energy above the transition state for the ketone hydrogenation step. The formation of the dihydride is entropically unfavorable. The theoretical activation barrier for H2 splitting is lowered by 5 kcal/mol by an alcohol-assisted mechanism but still remains higher in energy than the ketone hydrogenation step. This latter step can also be alcohol-assisted and can result in a different ee in the product alcohol than without alcohol assistance, as observed experimentally for reactions using 2-propanol versus benzene as the solvent. With alcohol present, an alkoxohydridoruthenium(II) complex is calculated to be the catalyst resting state.

Preparation of hydride complexes of ruthenium with bidentate phosphite ligands

Hydride complex RuH 2(PFFP) 2 ( 1) [PFFP = (CF 3CH 2O) 2PN(CH 3)N(CH 3)P(OCH 2CF 3) 2] was prepared by allowing the compound RuCl 4(bpy) · H 2O (bpy = 1,2-bipyridine) to react first with the phosphite PFFP and then with NaBH 4. Chloro-complex RuCl 2(PFFP) 2 ( 2) was also prepared, either by reacting RuCl 4(bpy) · H 2O with PFFP and zinc dust or by substituting triphenylphosphine with PFFP in the precursor complex RuCl 2(PPh 3) 3. Hydride derivative RuH 2(POOP) 2 ( 3) (POOP = Ph 2POCH 2CH 2OPPh 2) was prepared by reacting compound RuCl 3(AsPh 3) 2(CH 3OH) first with the phosphite POOP and then with NaBH 4. Depending on experimental conditions, treatment of carbonylated solutions of RuCl 3 · 3H 2O with POOP yields either the cis- or trans-RuCl 2(CO)(PHPh 2)(POOP) ( 4) derivative. Reaction of both cis- and trans- 4 with LiAlH 4 in thf affords dihydride complex RuH 2(CO)(PHPh 2)(POOP) ( 5). Chloro-complex all- trans-RuCl 2(CO) 2(PPh 2OMe) 2 ( 6) was obtained by reacting carbonylated solutions of RuCl 3 · 3H 2O in methanol with POOP. Treatment of chloro-complex 6 with NaBH 4 in ethanol yielded hydride derivative all- trans-RuH 2(CO) 2(PPh 2OMe) 2 ( 7). The complexes were characterised spectroscopically and the X-ray crystal structures of complexes 1, 3, cis- 4 and 6 were determined.

Mesitylborane as a Bis(σ-B−H) Ligand: An Unprecedented Bonding Mode to a Metal Center

The new borane complex RuH2(η2:η2-H2BMes)(PCy3)2 (2) can be isolated in good yield by reaction of H2BMes with RuH2(η2-H2)2(PCy3)2 (1) or alternatively, by reacting the chloro dihydrogen complex RuHCl(η2-H2)(PCy3)2 (3) with lithium mesitylborohydride. 2 has been fully characterized by NMR and X-ray diffraction crystallography. A DFT/B3PW91 analysis shows that in 2, the H2BMes group is coordinated to the {RuH2(PCy3)2} fragment through two geminal σ-B−H bonds. This coordination involves σ-donation to the ruthenium and π back-bonding from the ruthenium to the vacant p orbital of the boron. These two geminal σ-B−H bonds are responsible for the short Ru−B distance (1.938 (4) Å by X-ray, 1.957 Å by DFT).

Ruthenium-Catalyzed Hydroboration and Dehydrogenative Borylation of Linear and Cyclic Alkenes with Pinacolborane

The bis(dihydrogen)ruthenium complex RuH2(H2)2(PCy3)2 (1) catalyzes efficiently the borylation of linear and cyclic alkenes with pinacolborane. Similar results are obtained by using RuH[(μ-H)2Bpin](σ-HBpin)(PCy3)2 (2) as catalytic precursor. Selective hydroboration into the corresponding linear pinacol boronate is achieved in the case of 1-hexene, 1-octene, styrene, and allylbenzene. In the case of styrene, phenethyl pinacolboronate is isolated in 87% yield. Faster conversions of HBpin are obtained by increasing the alkene:borane ratio, with less than 10% of alkene hydrogenation. Isomerization into trans-β-methylstyrene is observed in the case of allylbenzene. Dehydrogenative borylation is competitive with ethylene and cyclic alkenes with large rings. Hydroboration of cyclohexene is highly favored, whereas for cyclodecene, vinylboronate is produced with only traces of allylboronate. Cyclooctene provides the two unsaturated boron-attached products, vinyl- and allylboronate in a 1:3 ratio, whereas only allylboronate is obtained from cycloheptene. The coupling of cyclodecenyl pinacolboronate with the aryl bromide (CF3)2C6H3Br, using standard catalytic Suzuki−Miyaura conditions, gives the corresponding product (CF3)2C6H3(C10H17) in 85% yield. Mechanistic investigations allow the characterization of the hydrido(boryl)(ethylene) complex RuH(Bpin)(C2H4)(PCy3)2 (3) as a key intermediate in the catalytic cycle.

Temperature-Dependent Coordination of Phosphine to Five-Coordinate Alkenylruthenium Complexes

The red, five-coordinate complexes Ru(CO)Cl(PPh(3))2(CH=CHPh) and [Ru(CO)Cl(PPh(3))2]2(mu-CH=CHC(6)H(4)CH=CH) undergo reversible coordination of PPh(3) at low temperature to produce the pale yellow, six-coordinate complexes Ru(CO)Cl(PPh(3))3(CH=CHPh) and [Ru(CO)Cl(PPh(3))3]2(mu-CH=CHC(6)H(4)CH=CH). X-ray crystal structures of the latter complex and of the hydride complex RuH(CO)Cl(PPh(3))3 were obtained. 1H and 31P NMR spectra between 20 and -70 degrees C exhibit large changes in both equilibrium constants and dynamic effects. Thermodynamic parameters, DeltaH = -17.5 +/- 2.0 kcal/mol and DeltaS = -57.5 +/- 7.6 eu, were obtained for PPh(3) coordination to the monoruthenium complex, and activation parameters, DeltaH = 20.6 +/- 0.7 kcal/mol and DeltaS = 41.6 +/- 2.0 eu, were obtained for the reverse decoordination. Coordination of PPh(3) was not observed upon cooling of the shorter bridged complex, [Ru(CO)Cl(PPh(3))2]2(mu-CH=CHCH=CH).

Synthesis, Neutron Structure, and Reactivity of the Bis(dihydrogen) Complex RuH2(η2-H2)2(PCyp3)2 Stabilized by Two Tricyclopentylphosphines

Treatment of Ru(eta4-C8H12)(eta6-C8H10) with 3 bar H2 in the presence of 2 equiv of tricyclopentylphosphine (PCyp3) in pentane resulted in the isolation of the new bis(dihydrogen) complex RuH2(eta2-H2)2(PCyp3)2 (2), characterized by NMR and single-crystal X-ray and neutron diffraction. The single-crystal neutron diffraction study is the first carried out for a bis(dihydrogen) complex. The coordination geometry around the metal center is a distorted octahedron defined by the two phosphines in a trans configuration (making an angle of 168.9(1) degrees ), two cis dihydrogen ligands, and two hydrides trans to them, defining the equatorial plane. The H-H bond distances (0.825(8) and 0.835(8) A) are characteristic of two "unstretched" dihydrogen ligands. H/D exchange between the Ru-H and the C-D bonds of deuterated benzene is observed within 1 h, leading to the formation of various isotopomers RuHxD6-x(PCyp3)2 (with x = 0-6). 2 is a catalyst precursor for ethylene coupling (20 bar, 293 K) to a functionalized arene (Murai reaction). We found a 90% conversion of acetophenone to 2-ethylacetophenone within 35 min, whereas 10 h was needed in the same conditions using the analogous tricyclohexylphosphine complex, RuH2(eta2-H2)2(PCy3)2, the best catalyst precursor, at room temperature, prior to this work.

Catalytic activity of dihydride ruthenium complexes in the hydrogenation of nitrogen containing heterocycles

The catalytic activity of the dihydride ruthenium complexes, RuH 2(CO) 2(P n Bu 3) 2, RuH 2(CO) 2(PPh 3) 2 and RuH 2(PPh 3) 4, in the hydrogenation of nitrogen containing heterocycles has been tested by analyzing the influence of reaction parameters such as temperature, hydrogen pressure, catalyst concentration, on the rate and regioselectivity of the reaction. RuH 2(PPh 3) 4 shows a better catalytic activity with an 86.7% conversion of quinoline after 24 h at 100 °C under a hydrogen pressure of 25 bar, while RuH 2(CO) 2(PPh 3) 2 and RuH 2(CO) 2(P n Bu 3) 2 in the same conditions give a conversion of 37.1% and 35.6%, respectively. These results are confirmed by the reaction rate of the hydrogenation of quinoline, since the K c in the presence of RuH 2(PPh 3) 4 (1.46 × 10 −5 s −1) is higher than others (6.37 × 10 −6 s −1 for RuH 2(CO) 2(PPh 3) 2 and 6.36 × 10 −6 s −1 for RuH 2(CO) 2(P n Bu 3) 2). Noteworthy is the selectivity of these catalytic systems in the hydrogenation of quinoline: in all tests the three catalysts lead to 1,2,3,4-tetrahydroquinoline as the major product, furthermore this compound is the only formed in the presence of RuH 2(CO) 2(PPh 3) 2. The selectivity is affected by the presence of an acid (CH 3COOH) or a base (N n Bu 3) in the reaction media. The complex RuH 2(PPh 3) 4 is catalytically active, even if in a minor extent, in the hydrogenation of isoquinoline, pyridine and 2-methylpyridine. The basicity of the substrate and steric hindrance around the nitrogen atom show a great influence on the conversion. The results obtained suggest that the catalytic system activates a heterocyclic ring through the coordination of the heteroatom to the metal centre of the complexes.