Complex RuHCl Research Articles

Direct Conversion of Alcohols to Acetals and H2 Catalyzed by an Acridine-Based Ruthenium Pincer Complex

The crystallographically characterized ruthenium complex RuHCl(A-(i)Pr-PNP)(CO) (1) [A-(i)Pr-PNP = 4,5-bis-(diisopropylphosphinomethyl)acridine], which bears a nonplanar acridine moiety, catalyzes in a neutral medium the transformation of primary alcohols to the corresponding acetals with the liberation of H(2). In the presence of base, complex 1 catalyzes the dehydrogenative coupling of alcohols to form esters. Acetal formation may involve hemiacetal dehydration to form an enol ether followed by alcohol addition to the double bond.

Ruthenium hydrogenation catalysts with P–N–N–P ligands derived from 1,3-diaminopropane and the formation of a β-diiminate complex by a base-induced isomerization

The complexes RuHCl{PPh 2(2-C 6H 4)CH NCH 2CH 2CH 2N CH(2-C 6H 4)PPh 2} (RuHCl{prP 2N 2}, 7) and RuHCl{PPh 2(2-C 6H 4)CH 2NHCH 2CH 2CH 2NHCH 2(2-C 6H 4)PPh 2} (RuHCl{prP 2(NH) 2}, 8) are prepared by reaction of RuHCl(PPh 3) 3 with a ligand derived from 1,3-diaminopropane and ortho-diphenylphosphinobenzaldehyde. They are active precatalysts for the hydrogenation of acetophenone and are moderately active for the hydrogenation of benzonitrile and imines. The related complex RuHCl{ethP 2(NH) 2} with a ligand derived from 1,2-diaminoethane provides a more active catalyst. Complexes 7 and 8 undergo an unusual base-promoted isomerization reaction that produces a ruthenium complex containing a novel β-diiminato ligand.

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.

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).

Novel hydrido-ruthenium(ii) complexes with histidine derivatives and their application in the hydrogenation of ketones

The complexes RuHCl((R)-binap)(L-NH2) with L-NH2 = (S)-histidine-Me-ester (1), histamine (3), (S)-histidinol (4) or 1-Me-(S)-histidine-Me-ester (5), and RuHCl((S)-binap)(L-NH(2)) with L-NH2 = (S)-histidine-Me-ester (2) have been prepared in 60-81% overall yields in a one-pot, three-step procedure from the precursor RuCl2(PPh3)3. Their octahedral structures with hydride trans to chloride were deduced from their NMR spectra and confirmed by the results of a single crystal X-ray diffraction study for complex 3. Under H2 and in the presence of KOtBu, complexes 1-5 in 2-propanol form moderately active catalyst precursors for the asymmetric hydrogenation of acetophenone to 1-phenylethanol. Complex 5 is more active and enantioselective than complexes 1-4, allowing complete conversion to 1-phenylethanol in 46% e.e. (R) in 72 h at 20 degrees C under 1 MPa of H2 with substrate : catalyst : base = 2000 : 1 : 30. Complex 5, when activated, also catalyzes the hydrogenation of trans-4-phenyl-3-buten-2-one to exclusively the allyl alcohol 4-phenyl-3-buten-2-ol under 2.7 MPa of H2 at 50 degrees C in 2-propanol. This selectivity for C=O versus C=C hydrogenation is consistent with a mechanism involving the outer sphere transfer of hydride and proton to the polar bond. Further extensions to complexes with peptides with N-terminal histidine groups appear feasible on the basis of the current work.

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 of Ruthenium Hydride Complexes Containing beta-Aminophosphine Ligands Derived from Amino Acids and their use in the H2-Hydrogenation of Ketones and Imines

The new complexes RuHCl(PPh2CH2CHRNH2)2 and RuHCl(PPh2CH2CHRNH2)(R- binap), R=H (Pgly), R=Me [(R)-Pala] were prepared by the substitution of the PPh3 ligands in RuHCl(PPh3)3 or RuHCl(PPh3)[(R)-binap] with beta-aminophosphines derived from amino acids. The complex trans-RuHCl(Pgly)[(R)-binap] has been characterized by X-ray crystallography. The complex trans-RuHCl[(S)-Ppro]2 where (S)-Ppro is derived from proline was also prepared and characterized by X-ray crystallography. These were used as catalyst precursors in the presence of a base (KOPr-i or KOBu-t) for the hydrogenation of various ketones and imines to the respective alcohols and amines with H2 gas (1–11 atm) at room temperature. Acetophenone was hydrogenated to (S)-1-phenylethanol in low ee (up to 40%) when catalyzed by the enantiomerically pure complexes. These complexes are especially active in the hydrogenation of sterically congested and electronically deactivated ketones and imines and are selective for the hydrogenation of CO bonds over CC bonds.

N-Heterocyclic Carbenes as Activating Ligands for Hydrogenation and Isomerization of Unactivated Olefins

The new hydridoruthenium complexes RuHCl(CO)(NHC)(PPh3) (NHC = IMes (4a), H2IMes (4b)), conveniently accessible from RuHCl(CO)(PPh3)3, exhibit high activity for hydrogenation of unactivated internal olefins and isomerization of terminal olefins. The lability of the PPh3 ligand is fundamental to the utility of 4: where this group is replaced by the relatively nonlabile PCy3 ligand, the activating effect of the N-heterocyclic carbene is suppressed.

Asymmetric Hydrogenation of Ketones Catalyzed by Ruthenium Hydride Complexes of a Beta-aminophosphine Ligand Derived from Norephedrine

A series ruthenium complexes with the chiral P−N ligand (1R,2R)-PPh2CHPhCHMeNH2 derived from (1S,2R)-norephedrine are synthesized starting from the complexes RuHCl(PPh3)3 or RuHCl(P−P)(PPh3) (P−P= (R)-binap or (S)-binap). These are precatalysts for the efficient asymmetric hydrogenation of simple ketones. For the hydrogenation of acetophenone to 1-phenylethanol, the enantioselectivity observed can be related to the structure of the precatalysts determined by X-ray diffraction. This relationship breaks down for the hydrogenation of pinacolone.

Dehalogenation of Hexachlorocyclohexanes and Simultaneous Chlorination of Triethylsilane Catalyzed by Rhodium and Ruthenium Complexes

Complexes RhCl(PPh3)3 and RhH2Cl(PiPr3)2 catalyze the dehalogenation of γ-hexachlorocyclohexane to benzene and the simultaneous chlorination of HSiEt3 to ClSiEt3. In the presence of RhCl(PPh3)3, the dehalogenation is inhibited by addition of PPh3. 1H and 31P{1H} NMR spectroscopy studies at variable temperature, on the behavior of the complex RhCl(PPh3)3 in the presence of γ-hexachlorocyclohexane and/or HSiEt3, indicate that the catalytic reaction involves the initial interaction of the catalyst with the silane and that chloro−hydride intermediates related to RhH2Cl(PPh3)3 are the main species during the catalysis. The complexes RuHCl(PPh3)3, RuH2Cl2(PiPr3)2, and RuHCl(η2-H2)(PiPr3)2 also catalyze the dehalogenation of γ-hexachlorocyclohexane and the simultaneous chlorination of HSiEt3 to ClSiEt3. In these cases, the dehalogenation products are 6/4 cyclohexene/cyclohexane (RuHCl(PPh3)3) and 4/6 cyclohexene/benzene (RuH2Cl2(PiPr3)2 and RuHCl(η2-H2)(PiPr3)2) mixtures. The dehalogenations of α- and δ-hexachlo...

OsHCl(CO)(PiPr3)2 as catalyst for ring-opening metathesis polymerization (ROMP) and tandem ROMP–hydrogenation of norbornene and 2,5-norbornadiene

Complex OsHCl(CO)(PiPr3)2 catalyzes the ring-opening metathesis polymerization (ROMP) of norbornene and 2,5-norbornadiene to give poly(norbornene) and poly(norbornadiene), respectively. In both cases the resulting polymers have a high cis (74–95%) content. The stereoregularity or tacticity of the cyclopentane and cyclopentene ring sequences in poly(norbornene) and poly(norbornadiene) estimated from the 13C{1H} NMR spectra of the hydrogenated derivatives was found to be syndiotactic. Complex OsHCl(CO)(PiPr3)2 is also active in tandem ROMP–hydrogenation of norbornene and 2,5-norbornadiene. At 40 °C and 3 atm of H2, poly(norbornene) is fully hydrogenated in 48 h, while poly(norbornadiene) is fully hydrogenated in 48 h at 75 °C and 3 atm of H2. The complex RuHCl(CO)(PiPr3)2 is also active in ROMP and tandem ROMP–hydrogenation of norbornene, obtaining trans-poly(norbornene) and hydrogenated poly(norbornene), respectively.

RuHCl(diphosphine)(diamine): Catalyst Precursors for the Stereoselective Hydrogenation of Ketones and Imines1

New chiral complexes RuHCl(diphosphine)(diamine) are readily prepared from RuHCl(PPh3)3. The diamine complexes, in the presence of alkoxide base, catalyze the hydrogenation of a wide variety of ketones and imines at 3 atm H2, 20 °C, including prochiral imines to chiral amines in good to excellent enantiomeric excess.

Factors governing the equilibrium between metalalkyl, alkylidene and alkylidyne: MCX2R, XMCXR and X2MCR

The reactions of vinyl ethers, H2CCH(OR), with RuHClL2 (L=PiPr3) furnish the carbene complexes RuHCl[C(CH3)(OR)]L2 by H migration. Os(H)3ClL2 serves as a surrogate for unknown OsHClL2, to give the analogous carbene, but this transforms further for RPh to give the carbyne OsHCl(OPh)(CCH3)L2. DFT calculations furnish insight into the relative thermodynamic stability of the various isomeric species, and are consistent with the major influence of π-donation by OR, as well as the preference of Os (versus Ru) for saturation and higher oxidation state. Comparison of the reactivity of H2CCHD0 (D0=π-donor) towards MHClL2 versus Cp2ZrHCl shows the dominant influence of metal π-donor power. Ruthenium and osmium complexes containing an MCF3 subunit show remarkably facile isomerization to FMCF2 carbenes.

ROMP using heterocyclic carbenes bearing a hydride ligand. An improved synthesis of RuCl2(PR3)2(CHMe)

The cyclic, heteroatom-stabilized carbene complexes RuHCl(PR3)2[C(X)C3H6] (R = Pri, Cy; X = O, NH) catalyze the ring-opening metathesis polymerization of 2-norbornene to give mainly (85%) trans-polynorbornene (Mw 1.1–2.0 × 105 g mol−1) in arene solvent at 30–80 °C. Initiation is slow, but not dependent on free phosphine concentration because the catalyst has an empty coordination site cis to the carbene. Protonation of RuHCl(PR3)2[C(OR)R′] species occurs at the hydride ligand, and the acidity of the resulting species leads to C–OR bond cleavage. This leads to facile conversion of RuHClL2[C(OEt)Me] to RuCl2L2[CHMe] and EtOH by HCl and, thus, a convenient new synthesis of a traditional metathesis catalyst whose carbene source is H2CC(OEt)H.

Hydrogenolysis of a ruthenium carbene complex to yield dihydride-dihydrogen tautomers: mechanistic implications for tandem ROMP-hydrogenation catalysis.

Conversion of Grubbs's catalyst 1 into a hydrogenation catalyst is described. Hydrogenolysis of the Ru−carbene bond in CH2Cl2 yields Ru(IV) species 2; in other solvents, a mixture of 2 and its dihydrogen tautomer 4 is formed, even in the presence of base. Further reaction gives hydridochloro complex RuHCl(H2)(PCy3)2 3, which reverts to 2 in CH2Cl2.

Simultaneous Dehalogenation of Polychloroarenes and Chlorination of HSiEt3 Catalyzed by Complexes of the Groups 8 and 9

The catalytic activity of the complexes FeCl2(PPh3)2, RuHCl (PPh3)3, RuH2(CO)(PPh3)3, RuHCl(CO)(AsPh3)3, RuHCl(CO) (PiPr3)2, OsHCl(CO)(PiPr3)2, OsH2Cl2(PiPr3)2, CoCl(PPh3)3, RhH2Cl(PiPr3)2, IrH2Cl(PiPr3)2, IrCl(PPh3)3, and IrH2(SiEt3) (COD)(PCy3) (COD=1,5-cyclooctadiene) in the simultaneous dehalogenation of 1,2,4-trichlorobenzene and the chlorination of HSiEt3 has been studied. The 3d metal complexes and the derivative IrH2(SiEt3)(COD)(PCy3) are unactive, while the 4d and 5d metal compounds simultaneously catalyze the dehalogenation of 1,2,4-trichlorobenzene and the chlorination of HSiEt3. The osmium and iridium derivatives are less effective catalysts than the derivatives of ruthenium and rhodium and undergo deactivation. Complexes RuHCl(PPh3)3 and RhH2Cl(PiPr3)2 also catalyze the dehalogenation of 1,2-, 1,3-, and 1,4-dichlorobenzene and chlorobenzene. The dehalogenation of 1,3- and 1,4-dichlorobenzene is favored over the dehalogenation of the 1,2-isomer.

Hydroruthenation of Propargyl Amines Promoted by the 16-Electron Complex RuHCl(CO)(PiPr3)2

The 16-electron complex RuHCl(CO)(PiPr3)2 (1) reacts with propargyl amines H‒C≡C(CH2) n Y (2–5) (n=1,2; Y = NMe2, N(Me)CH2Ph, or Py) by insertion to afford the five-coordinate vinyl-complexes RuCl{(E)‒CH˭CH(CH2) n Y}(CO)(PiPr3)2 (6, Y = NMe2, n = 1; 7, Y = N(Me)CH2Ph, n = 1; 8, Y = Py, n = 2; 9, Y = NMe2, n = 2) in good yield. Addition of CO to 7 produces the six-coordinate vinyl-complex RuCl{(E)‒CH˭CH(CH2) n Y}(CO)2(PiPr3)2 (10). The trans stereochemistry at the C˭C bond is observed in all compounds. All compounds were characterized by IR, 1H, 13C and 31P NMR spectroscopy.

14-Electron Four-Coordinate Ru(II) Carbyl Complexes and Their Five-Coordinate Precursors: Synthesis, Double Agostic Interactions, and Reactivity

The structure of five-coordinate Ru(II) complexes RuHCl(CO)(PiPr3)2, 1, RuCl2(CO)(PiPr3)2, 2, and Ru(Ph)Cl(CO)(PtBu2Me)2, 12, are reported. All three of these complexes have square-based pyramid geometry with the strongest σ-donor ligand trans to the vacant site. These 16-electron complexes do not show bona fide agostic interactions. This is attributed to the strong trans influence ligand (H, CO, and Ph) and π-donation of the Cl, which is further supported by the fact that two agostic interactions are present in the Cl- removal product of 12, i.e., the four-coordinate [RuPh(CO)L2]BAr‘4 (L = PtBu2Me, Ar‘ = 3,5-C6H3(CF3)2), 16. Structural comparison of 16 and 12 reveals that removal of Cl- does not change the remaining ligand arrangements but creates two low-lying LUMOs for agostic interactions, which persist in solution as evidenced by IR spectroscopy. Reactions of 16 with E−H (E = B, C(sp)) bonds cleave the Ru−Ph bond and form Ru−E/H bonds by different mechanisms. The reaction with catecholborane gives [RuH(CO)L2]BAr‘4, which further reacts with catecholborane to give [Ru(BR2)(CO)L2]BAr‘4. However, the reaction with Me3SiCCH undergoes a multistep transformation to give a PhCCSiMe3- and Me3SiCCH-coupled product, the mechanism of which is discussed. Reaction of RuCl2(CO)L2 with 1 equiv MeLi affords RuMeCl(CO)L2, 5, which further reacts with MeLi forming RuMe2(CO)L2, 7. Variable-temperature 13C{1H} NMR spectra reveal the two methyls in 7 are inequivalent and exchange by overcoming an energy barrier of 6.8 kcal/mol at −30 °C. The chloride of 5 can be removed to give [RuMe(CO)L2]BAr‘4.

Dimeric and polymeric ruthenium complexes with Ru—vinyl linkages

Abstract The carbonyl hydrido complex RuHCl(CO)(PPh 3 ) 3 reacted with diynes HC≡C-R-C≡CH (R = p -C 6 H 4 , p -C 6 H 4 -C 6 H 4 ) to give the five-coordinate vinyl ruthenium dimeric compounds [RuCl(CO)(PPh 3 ) 2 ] 2 (μ-CH=CH-R-CH=CH) in high yields. Additions of 2,6-di-methylphenyl isocyanide (CNC 8 H 9 ) or 4-phenylpyridine (Ph-Py) to the vinyl complexes produced the six-coordinate adducts [RuCl(CO)(C 8 H 9 NC)(PPh 3 ) 2 ] 2 (μ-CH=CH-R-CH=CH) and [RuCl(CO)(Ph-Py)(PPh 3 ) 2 ] 2 (μ-CH=CH-R-CH=CH) respectively. Reactions of [RuCl(CO)(PPh 3 ) 2 ] 2 (μ-CH=CH-R-CH=CH) with L (L = 2,3,5,6-tetramethylphenyl diisocyanide or 4,4′-bipyridine) produced [RuCl(CO)(PPh 3 ) 2 (μ-CH=CH-R-CH=CH)RuCl(CO)(PPh 3 ) 2 (μ-L)] x .