Ruthenium(II)-Catalyzed Transfer Hydrogenation of Aromatic and Heteroaromatic Aldehydes in Air

Aromatic and heteroaromatic aldehydes are efficiently reduced to their corresponding alcohols in the presence of [RuCl₂(p-cymene)]₂ and KOAc in 2-propanol under air at 80 °C. The presence of KOAc in the reaction is essential; in its absence no reduction takes place. A highly efficient, external-base-free reduction of aldehydes has also been reported with (η⁶-arene)ruthenium(II) complexes containing O^O chelate ligand such as [Ru(OAc)₂(p-cymene)] and [RuCl(KA)(p-cymene)], obtaining alcohol in excellent yield (OAc, acetate; KA, kojic acetate). The scope of the reaction has been extended to a broad range of aromatic and heteroaromatic aldehydes.     

Preparation and reactivity of p-cymene complexes of ruthenium and osmium incorporating 1,3-triazenide ligands

p-Cymene complexes MCl₂(η⁶-p-cymene)L [M = Ru, Os; L = P(OEt)₃, PPh(OEt)₂, (CH₃)₃CNC] were prepared by allowing [MCl(μ-Cl)(η⁶-p-cymene)]₂ to react with phosphites or tert-butyl isocyanide. Treatment of MCl₂(η⁶-p-cymene)L complexes with 1,3-ArNNN(H)Ar triazene and an excess of NEt₃ gave the cationic triazenide derivatives [M(η²-1,3-ArNNNAr)(η⁶-p-cymene)L]BPh₄ (Ar = Ph, p-tolyl). Neutral triazenide complexes MCl(η²-1,3-ArNNNAr)(η⁶-p-cymene) (M = Ru, Os) were also prepared by allowing [MCl(μ-Cl)(η⁶-p-cymene)]₂ to react with 1,3-diaryltriazene in the presence of triethylamine. p-Cymene complexes MCl₂(η⁶-p-cymene)L reacted with equimolar amounts of 1,3-ArNNN(H)Ar triazene to give both triazenide complexes [M(η²-1,3-ArNNNAr)(η⁶-p-cymene)L]BPh₄ and amine derivatives [MCl(ArNH₂)(η⁶-p-cymene)L]BPh₄. A reaction path for the formation of the amine complex is also reported. The complexes were characterised by spectroscopy and X-ray crystallography of RuCl₂(η⁶-p-cymene)[PPh(OEt)₂] and [Ru(η²-1,3-p-tolyl-NNN-p-tolyl)(η⁶-p-cymene){CNC(CH₃)₃}]BPh₄. Selected triazenide complexes were studied as catalysts in the hydrogenation of 2-cyclohexen-1-one and cinnamaldehyde.     

Coordination and Hydroboration of Ru(II)-Borate Complexes: Dihydridoborate vs. Bis(dihydridoborate)

Treatment of [Cp*RuCl₂]₂, 1 , [(COD)IrCl]₂, 2 or [(p-cymene)RuCl₂]_2, 3 (Cp*=η⁵-C₅Me_5, COD= 1,5-cyclooctadiene and p-cymene=η⁶-ⁱPrC₆H₄Me) with heterocyclic borate ligands [Na[(H₃B)L], L₁ and L₂ ( L₁ : L=amt, L₂ : L=mp; amt=2-amino-5-mercapto-1,3,4-thiadiazole, mp=2-mercaptopyridine) led to the formation of borate complexes having uncommon coordination. For example, complexes 1 and 2 on reaction with L₁ and L₂ afforded dihydridoborate species [L^AM(μ-H)₂BHL] 4 – 6 ( 4 : L^A=Cp*, M=Ru, L=amt; 5 : L^A=Cp*, M=Ru, L=mp; 6 : L^A=COD, M=Ir, L=mp). On the other hand, treatment of 3 with L₂ yielded cis- and trans-bis(dihydridoborate) species, [Ru{(μ-H)₂BH(mp)}₂], cis- 7 and trans- 7 . The isolation and structural characterization of fac- and mer-[Ru{(μ-H)₂BH(mp)}{(μ-H)BH(mp)₂}], 8 from the same reaction offered an insight into the behaviour of these dihydridoborate species in solution. Fascinatingly, despite having reduced natural charges on Ru centres both at cis-and trans- 7 , they underwent hydroboration reaction with alkynes that yielded both Markovnikov and anti-Markovnikov addition products, 10 a – d .     

Synthesis of N-heterocyclic carbene precursors bearing biphenyl units and their use in ruthenium-catalyzed ring-opening metathesis polymerization

A range of new imidazolium and imidazolinium chlorides bearing biphenyl units on their nitrogen atoms was synthesized. They differed by the electron-withdrawing or -donating nature and the steric bulk of the substituents on their aromatic rings. These various N-heterocyclic carbene (NHC) precursors were combined with the [RuCl₂(p-cymene)]₂ dimer and potassium tert-butoxide to generate the corresponding ruthenium-arene complexes [RuCl₂(p-cymene)(NHC)] in situ. The catalytic activity of these species was investigated in the photoinduced ring-opening metathesis polymerization (ROMP) of cyclooctene. The results obtained confirmed the necessity of blocking the ortho-positions of the phenyl rings in the vicinity of the metal center in order to attain high catalytic efficiencies. They also showed that changing the steric and electronic properties of the substituents on the remote phenyl rings of the biphenyl units had no significant influence on the outcome of the polymerization.     

Syntheses of (η6-p-cymene)ruthenium(II) piano-stool amine complexes: molecular structure of [(η6-C10H14)RuCl2(H2N-C6H4-p-Cl)]

The dimeric complex [{(η⁶-p-cymene)Ru(μ-Cl)Cl}₂] (1) reacts with S,N-donor Schiff base ligands, para-substituted S-(thiophen-2-ylmethylene)phenylamines in methanol to give mononuclear amine complexes of the type [(η⁶-p-cymene)RuCl₂(NH₂–C₆H₄–p-X)] {X?=?H (2a); X?=?CH₃ (2b); X?=?OCH₃ (2c); X?=?Cl (2d); Br (2e) X?=?NO₂ (2f), respectively} by hydrolysis of the imine group of the ligand after coordination to the metal. The complexes were characterized by analysis and IR and NMR spectroscopy. The molecular structure of [(η⁶-C₁₀H₁₄)RuCl₂(H₂N–C₆H₄–p-Cl)] (2d) was established by a single-crystal X-ray diffraction study.     

Syntheses and Structures of Homo‐ and Heterobimetallic Complexes Containing a (Cyclopentadienone)rhodium(I) Fragment

The reaction of [RhCl(η⁴‐Ph₂R₂C₄CO)]₂ (R=Ph, 2‐naphthyl) with the dimeric complexes [RuCl₂(p‐cymene)]₂ p‐cymene=1‐methyl‐4‐(1‐methylethyl)benzene, [RuCl₂(1,3,5‐Et₃C₆H₃)]₂, [MCl₂(Cp*)]₂ (M=Rh, Ir; Cp*=1,2,3,4,5‐pentamethylcyclopenta‐2,4‐dien‐1‐yl), [RuCl₂(CO)₃]₂, [RuCl₂(dcypb)(CO)]₂ (dcypb=butane‐1,4‐diylbis[dicyclohexylphosphine]), [(dppb)ClRu(μ‐Cl)₂(μ‐OH₂)RuCl(dppb)] (dppb=butane‐1,4‐diylbis[diphenylphosphine]), and [(dcypb)(N₂)Ru(μ‐Cl)₃RuCl(dcypb)] was investigated. In all cases, mixed, chloro‐bridged complexes were formed in quantitative yield (see 5 – 8, 9 – 16, 18, 19, 21 , and 22 ). The six new complexes 5, 8, 9, 13, 15 , and 22 were characterized by single‐crystal X‐ray analysis (Figs. 1–3).     

In situ‐generated Ru(III)‐mediated ATRP from the polymeric Ru(III) complex in the absence of activator generation agents

Past research has examined the atom transfer radical polymerization (ATRP) with high oxidation state metal complexes and without the need for any additives such as reducing agent or free radical initiator. To extend this research, half‐metallocene ruthenium(III) (Ru(III)) catalysts were used for the polymerization of methyl methacrylate (MMA) for the first time. These catalysts were generated in situ simply by mixing phosphorus‐containing ligand and pentamethylcyclopentadienyl (Cp*) Ru(III) polymer ((Cp*RuCl₂)_n). The complexes in their higher oxidation state such as Cp*RuCl₂(PPh₃) were air‐stable, highly active, and removable catalysts for the ATRPs of MMA with both precision control of molecular weight and narrow polydispersity index. The addition of ppm amount of metal catalyst contributed to the formation of very well‐defined homopolymers and copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Photoinduced ring opening metathesis polymerization (PROMP) of strained bicyclic olefins with ruthenium complexes of the type [(η6-arene1)Ru(η6-arene2)]2+ and [Ru(Nc-R)6]2+

Upon UV irradiation, the complexes [(η⁶-arene₁)Ru(η⁶-arene₂)]²⁺ (toluene-4-sulfonate or trifluormethane-sulfonate as counter ion; examples for arene: benzene, toluene, mesitylene, hexamethylbenzene, anisole, biphenyl, naphthalene) and [Ru(NC-R)₆]²⁺ (tosylate or triflate as counter iron; R = methyl, ethyl, phenyl) are transformed into active catalysts for ring opening metathesis polymerization (ROMP) of strained bicyclic olefins. The photoinduced ring opening metathesis polymerization (PROMP) is most efficient with sandwich complexes having high quantum yields for the photochemically induced solvation of [(η⁶-arene₁)Ru(η⁶-arene₂)]²⁺ to [Ru(solvent)₆]²⁺. With most of the complexes no (or only low) catalytic activity is observed in the absence of light. After the photolysis step, the mechanism of the polymerzation is identical to ROMP reactions with thermally activated ruthenium catalysts. Good yields and high molecular weights are obtained with a catalyst concentration of 0.1–1%. A mechanistic model for the initiation is presented. © 1995 John Wiley & Sons, Inc.     

Water soluble Ru (II)–p‐cymene complexes of chiral aroylthiourea ligands derived from unprotected D/L‐alanine as proficient catalysts for asymmetric transfer hydrogenation of ketones

The newfangled chiral aroylthiourea ligands (L1‐L6) were produced from unprotected D/L‐alanine and their water soluble Ru (II) organometallic catalysts ( 1 – 6 ) were designed from their reaction with [RuCl₂(η⁶‐p‐cymene)]₂. The analytical and spectral methods were used to confirm the structure of the ligands and complexes. The solid state structure of L1, 5 and 6 was confirmed by single crystal XRD. The organometallic compounds ( 1 – 6 ) catalyzed the asymmetric transfer hydrogenation of aromatic, heteroaromatic and bulky ketones to yield respective enantiopure secondary alcohols with admirable conversions (up to 99%) and attractive enantiomeric excesses (ee up to 98%), in presence of formic acid and triethylamine in water medium under non‐inert atmospheric conditions.     

Isocyanate‐ and Isothiocyanate‐Derived RuIV‐Based Alkylidenes: Synthesis,Structure, and Activity

The synthesis and characterization of a series of isocyanate‐ and isothiocyanate‐derived second generation Grubbs–Hoveyda‐type ruthenium–alkylidene complexes, that is, [Ru(N?C?O)₂(IMesH₂)(?CH‐2‐(2‐PrO)‐C₆H₄)] ( 1 ), [Ru(N?C?O)₂(1,3‐dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene)(=CH‐2‐(2‐PrO)‐C₆H₄)] ( 2 ), [Ru(N?C?S)₂(IMesH₂)(?CH‐2‐(2‐PrO)‐C₆H₄)] ( 3 ), and [Ru(N?C?S)₂(1,3‐dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene)(?CH‐2‐(2‐PrO)‐C₆H₄)] ( 4 ), and their activity in various metathesis reactions are described. Compounds 1 – 4 were prepared by reaction of the parent complexes [RuCl₂(IMesH₂)(?CH‐2‐(2‐PrO)C₆H₄)] ( 5 ) (IMesH₂=1,3‐bis‐(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene) and [RuCl₂(1,3‐dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene)(?CH‐2‐(2‐PrO)‐C₆H₄)] ( 6 ) with silver cyanate and thiocyanate, respectively. The X‐ray structure of 1 was determined, confirming the isocyanate‐type bonding of the ligand. The isothiocyanate‐type bonding in 3 and 4 was unambiguously confirmed by IR and ¹³C NMR spectroscopy. The isocyanate‐derived complexes 1 and 2 were found to be excellent catalysts for the ring‐opening metathesis polymerization (ROMP) of cis‐cycloocta‐1,5‐diene (COD). Both 1 and 2 yielded poly(COD) with a trans‐content of about 80 %. First‐order kinetics with unprecedentedly high rate constants of polymerization (k_p=0.068 and 0.26 s^?1, respectively) were observed. Compounds 3 and 4 were also active initiators for the ROMP of COD, however, they generated poly(COD) with a cis‐content of 80 and 67 %, respectively. Complexes 1 and 2 also showed good catalytic activity in cross‐metathesis (CM) reactions. Finally, 1 – 4 were also found to be excellent catalysts for the regioselective cyclopolymerization of diethyl 2,2‐dipropargylmalonate (DEDPM), resulting in poly(DEDPM) almost entirely based on five‐membered repeat units, that is, cyclopent‐1‐ene‐1,2‐vinylenes.     

Tailored norbornene-based copolymer with systematic variation of norbornadiene as a crosslinker obtained via ROMP with alternative amine Ru catalysts

Copolymers of norbornene (NBE) with norbornadiene (NBD) were obtained via ROMP with [RuCl₂(PPh₃)₂(L)] type complexes as initiators (1 for L = piperidine and 2 for L = 3,5-Me₂piperidine). The reactions were performed using a fixed quantity of NBE (5000 equivalents/[Ru]) for different concentrations of NBD (500, 1000, 1500 and 2000 equivalents/[Ru]) in CHCl₃, initiated with ethyl diazoacetate at room temperature. The presence of NBD in the NBE chains was characterized by ¹H and ¹³C NMR. Whereas the copolymer microstructure was influenced neither by the NBD quantity nor by the initiator type, the M_n and PDI values were improved when increasing the NBD quantity in the medium. When raising the NBD amount, DMA results indicated increased cross-linking with increasing T_g and E′ storage modulus, as well as the fact that SEM micrographs indicated decreased pore sizes in the porous isolated copolymers.     

Syntheses and characterization of cyano-bridged homo and hetero bimetallic complexes containing η and η-cyclic hydrocarbons

The reactions of [(ind)Ru(PPh₃)₂CN] (ind = η⁵-C₉H₇) (1) and [CpRu(PPh₃)₂CN] (Cp = η⁵-C₅H₅) (2) with [(η⁶-p-cymene)Ru(bipy)Cl]Cl (bipy = 2,2′-bipyridine) (3) in the presence of AgNO₃/NH₄BF₄ in methanol, respectively, yielded dicationic cyano-bridged complexes of the type [(ind)(PPh₃)₂Ru(μ-CN)Ru(bipy)(η⁶-p-cymene)](BF₄)₂ (4) and [Cp(PPh₃)₂Ru(μ-CN)Ru(bipy)(η⁶-p-cymene)](BF₄)₂ (5). The reaction of [CpRu(PPh₃)₂CN] (2), [CpOs(PPh₃)₂CN] (6) and [CpRu(dppe)CN] (7) with the corresponding halide complexes and [(η⁶-p-cymene)RuCl₂]₂ formed the monocationic cyano-bridge complexes [Cp(PPh₃)₂Ru(μ-CN)Os(PPh₃)₂Cp](BF₄) (8), [Cp(PPh₃)₂Os(μ- CN)Ru(PPh₃)₂Cp](BF₄) (9) and [Cp(dppe)Ru(μ-CN)Os(PPh₃)₂Cp](BF₄) (10) along with the neutral complexes [Cp(PPh₃)₂Ru(μ-CN)Ru (η⁶-p-cymene)Cl₂] (11), [Cp(PPh₃)₂Os(μ-CN)Ru(η⁶-p-cymene)Cl₂] (12), and [Cp(dppe) Ru(μ-CN)Ru(η⁶-p-cymene)Cl₂] (13). These complexes were characterized by FT IR, ¹H NMR, ³¹P{¹H} NMR spectroscopy and the molecular structures of complexes 4, 8 and 11 were solved by X-ray diffraction studies.     

Modifying the structure of dinuclear ruthenium complexes with antitumor activity

In order to modulate the structure of a recently developed series of antitumor‐active, dinuclear Ru(II)–arene compounds, complexes 1c – 4c were synthesized. The complexes were modified with respect to their pyridinone moieties and the spacer linking the two metal centers. More particularly, the series of dinuclear ruthenium(II) complexes was extended to compounds with longer spacers, i.e. tetradecane and 3,7,10‐trioxotridecane, and the pyridinone ring was modified by replacing the methyl group by an ethyl group and by shifting the position of the methyl group. The organometallic ruthenium compounds were obtained from the reaction between [RuCl₂(η⁶‐p‐isopropyltoluene)]₂ and ligands 1b – 4b with yields ranging from 41 to 67%. All compounds were characterized by standard methods: MS, ¹H and ¹³C NMR spectroscopy and elemental analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermal decomposition of new chlorido(p-cymene) ruthenium(II) complexes containing N-alkylphenothiazines

The thermal decomposition of [RuCl₂(η⁶-p-cymene)]₂ (1) and its biologically active N-alkylphenothiazine compounds of composition L[RuCl₃(η⁶-p-cymene)] where L = CPH⁺ (2), TFH⁺·HCl (3), and TRH⁺ (4) (chlorpromazine hydrochloride, CP·HCl; trifluoperazine dihydrochloride, TF·2HCl; and thioridazine hydrochloride, TR·HCl, respectively) has been studied. The crystal and molecular structure of compound 3 was determined earlier by single crystal X-ray diffraction analysis. The thermal data were collected by simultaneous TG/DSC measurements. For evolved gas detection, the qualitative reaction of chlorides with AgNO₃ in an acidic solution was applied. The measurements were carried out in the temperature range to 700 °C in nitrogen atmosphere. Compounds of L[RuCl₃(η⁶-p-cymene)] crystallize with water or water/2-propanole. On the basis of thermal data, the trend in the solvent bonding energies was assessed.     

Arene ruthenium complexes of the thermally resistant ligand tri-2-pyridylamine

Summary The degradation-resistant ligand tri-2-pyridylamine (tripyam) (1) forms a variety of stable ruthenium complexes. Reaction of (1) with RuCl₂(PPh₃)₃ yields the complex RuCl₂(PPh₃)(tripyam) (2) and, upon prolonged heating in pyridine, forms RuCl₂(py)(tripyam) (3). Complexes (2) and (3) display unusual thermal stability, resisting degradation at temperatures of 270 °C. Reaction of (2) with two equivalents of AgSbF₆ in water yields the solvento complex [Ru(PPh₃)(tripyam)(OH₂)₂] (SbF₆)₂ (2a). Reaction of (1) with RuCl₃·H₂O also yields the trichloro complex RuCl₃(tripyam) (4). The organometallic precursor [RuCl₂(p-cymene)]₂ reacts with (1) and either two or four equivalents of AgSbF₆ to yield [RuCl(p-cymene)( ²-tripyam)]SbF₆ (5) and [Ru(p-cymene) ( ³-tripyam)](SbF₆)₂ (6), respectively. Each of these complexes has been characterized by spectroscopic techniques and, in the case of (5), by single-crystal X-ray diffraction.     

Strained Ruthenium Complexes Bearing Tridentate Guanidine-Derived Ligands

The dimer [{(η⁶-p-cymene)RuCl}₂(μ-Cl)₂] (cymene=MeC₆H₄ⁱPr) reacts with N,N′-bis(p-tolyl)-N′′-(2-pyridinylmethyl)guanidine ( H₂L1 ) and N,N′-bis(p-tolyl)-N′′-(2-diphenylphosphanoethyl)guanidine ( H₂L2 ), in the presence of NaSbF₆, giving rise to chlorido compounds of formula [(η⁶-p-cymene)RuCl( H₂L )][SbF₆] ( H₂L = H₂L1 ( 1 ), H₂L2 ( 2 )) in which the guanidine ligand adopts a κ² chelate coordination mode. The related ligand (S)-N,N′-bis(p-tolyl)-N′′-(1-isopropyl, 2-diphenylphosphano ethyl)guanidine ( H₂L3 ) affords mixtures of the corresponding chlorido compound [(η⁶-p-cymene)RuCl( H₂L3 )][SbF₆] ( 3 ) together with the complexes [(η⁶-p-cymene)RuCl₂( H₃L3 )][SbF₆] ( 4 ) and [(η⁶-p-cymene)Ru(κ³N,N′,P- HL3 )][SbF₆] ( 10 ) which contain phosphano-guanidinium and phosphano-guanidinate ions acting as monodentate and tridentate ligand, respectively. Compounds 1 , 2 and mixture of 3 / 4 / 10 react with AgSbF₆ rendering the cationic aqua-complexes [(η⁶-p-cymene)Ru( H₂L )(OH₂)][SbF₆]₂ ( H₂L = H₂L1 ( 5 ), H₂L2 ( 6 ), H₂L3 ( 7 )). These aqua-complexes exhibit a temperature-dependent fluxional process in solution. Experimental NMR studies and DFT theoretical calculations on complex 6 suggest that the process involves the exchange between two rotamers around one of the C−N guanidine bonds. Treatment of 5 – 7 with NaHCO₃ renders the complexes [(η⁶-p-cymene)Ru(κ³N,N′,N′′- HL1 )][SbF₆] ( 8 ) and [(η⁶-p-cymene)Ru(κ³N,N′,P- HL )][SbF₆] ( HL = HL2 ( 9 ), HL3 ( 10 )), respectively, in which the HL ligand adopts a fac κ³ coordination mode. The new complexes have been characterized by analytical and spectroscopic means, including the determination of the crystal structures of the compounds 1 , 2 , 5 , 9 and 10 , by X-ray diffractometric methods.     

Alternating Ring‐Opening Metathesis Copolymerization by Grubbs‐Type Initiators with Unsymmetrical N‐Heterocyclic Carbenes

A series of Ru^IV–alkylidenes based on unsymmetrical imidazolin‐2‐ylidenes, that is, [RuCl₂{1‐(2,4,6‐trimethylphenyl)‐3‐R‐4,5‐dihydro‐(3H)‐imidazol‐1‐ylidene}(CHPh)(pyridin)] (R=CH₂Ph ( 5 ), Ph ( 6 ), ethyl ( 7 ), methyl ( 8 )), have been synthesized. These and the parent initiators [RuCl₂(PCy₃){1‐(2,4,6‐trimethylphenyl)‐3‐R‐4,5‐dihydro‐(3H)‐imidazol‐1‐ylidene}(CHC₆H₅)] (R=CH₂C₆H₅ ( 1 ), C₆H₅ ( 2 ), ethyl ( 3 )) were used for the alternating copolymerization of norborn‐2‐ene (NBE) with cis‐cyclooctene (COE) and cyclopentene (CPE), respectively. Alternating copolymers, that is, poly(NBE‐alt‐COE)_n and poly(NBE‐alt‐CPE)_n containing up to 97 and 91 % alternating diads, respectively, were obtained. The copolymerization parameters of the alternating copolymerization of NBE with CPE under the action of initiators 1 – 3 and 5 – 8 were determined by using both a zero‐ and first‐order Markov model. Finally, kinetic investigations using initiators 1 – 3 , 6 , and 7 were carried out. These revealed that in contrast to the 2nd‐generation Grubbs‐type initiators 1 – 3 the corresponding pyridine derivatives 6 and 7 represent fast and quantitative initiating systems. Hydrogenation of poly(NBE‐alt‐COE)_n yielded a fully saturated, hydrocarbon‐based polymer. Its backbone can formally be derived by 1‐olefin polymerization of CPE (1,3‐insertion) followed by five ethylene units and thus serves as an excellent model compound for 1‐olefin polymerization‐derived copolymers.     

Water-soluble (η-arene)ruthenium(II)-phosphine complexes and their catalytic activity in the hydrogenation of bicarbonate in aqueous solution

The reactions of [(η⁶-C₆H₆)RuCl₂]₂ and [(η⁶-p-cymene)RuCl₂]₂ with hydrogen in the presence of the water-soluble phosphines tppts (meta-trisulfonated triphenylphosphine) and pta (1,3,5-triaza-7-phosphaadamantane) afforded as the main species [(η⁶-C₆H₆)RuH(tppts)₂]⁺, [(η⁶-C₆H₆)RuH(pta)₂]⁺, [(η⁶-p-cymene)RuH(tppts)₂]⁺ and [(η⁶-p-cymene)RuH(pta)₂]⁺. This latter complex was also formed in the reaction of [(η⁶-p-cymene)RuCl₂(pta)] and hydrogen with a redistribution of pta. In addition, prolonged hydrogenation at elevated temperatures and in the presence of excess of pta led to the formation of the arene-free [RuH(pta)₄Cl], [RuH(pta)₄(H₂O)]⁺, [RuH₂(pta)₄] and [RuH(pta)₅]⁺ complexes. Ru-hydrides, such as [(η⁶-arene)RuH(L)₂]⁺, catalyzed the hydrogenation of bicarbonate to formate in aqueous solutions at p(H₂)=100 bar, T=50-70 °C.     

Cationic versus neutral Ru(II)--N-heterocyclic carbene complexes as latent precatalysts for the UV-induced ring-opening metathesis polymerization

A series of cationic and neutral Ru^II complexes of the general formula [Ru(L)(X) (tBuCN)₄]⁺X^? and [Ru(L)(X)₂(tBuCN)₃)], that is, [Ru(CF₃SO₃){NCC(CH₃)₃}₄(IMesH₂)]⁺[CF₃SO₃]^? ( 1 ), [Ru(CF₃SO₃){NCC(CH₃)₃}₄(IMes)]⁺[CF₃SO₃]^? ( 2 ), [RuCl{NCC(CH₃)₃}₄(IMes)]⁺Cl^? ( 3 ), [RuCl{NCC(CH₃)₃}₄(IMesH₂)⁺Cl^?]/[RuCl₂{NCC(CH₃)₃}₃(IMesH₂)] ( 4 ), and [Ru(NCO)₂{NCC(CH₃)₃}₃(IMesH₂)] ( 5 ) (IMes=1,3‐dimesitylimidazol‐2‐ylidene, IMesH₂=1,3‐dimesityl‐imidazolin‐2‐ylidene) have been synthesized and used as UV‐triggered precatalysts for the ring‐opening metathesis polymerization (ROMP) of different norborn‐2‐ene‐ and cis‐cyclooctene‐based monomers. The absorption maxima of complexes 1 – 5 were in the range of 245–255 nm and thus perfectly fit the emission band of the 254 nm UV source that was used for activation. Only the cationic Ru^II‐complexes based on ligands capable of forming μ²‐complexes such as 1 and 2 were found to be truly photolatent in ROMP. In contrast, complexes 3 – 5 could be activated by UV light; however, they also showed a low but significant ROMP activity in the absence of UV light. As evidenced by ¹H and ¹³C NMR spectroscopy, the structure of the polymers obtained with either 1 or 2 are similar to those found in the corresponding polymers prepared by the action of [Ru(CF₃SO₃)₂(IMesH₂)(CH‐2‐(2‐PrO)‐C₆H₄)], which strongly suggest the formation of Ru‐based Grubbs‐type initiators in the course of the UV‐based activation process. Precatalysts that have the IMesH₂ ligand showed significantly enhanced reactivity as compared with those based on the IMes ligand, which is in accordance with reports on the superior reactivity of IMesH₂‐based Grubbs‐type catalysts compared with IMes‐based systems.     

Heterobimetallic Coinage Metal-Ruthenium Complexes Supported by Anionic N-Heterocyclic Carbenes

The lithium complexes [(WCA-NHC)Li(toluene)] of anionic N-heterocyclic carbenes with a weakly coordinating borate moiety (WCA-NHC, WCA=B(C₆F₅)₃, NHC=IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were used for the preparation of silver(I) or copper(I) WCA-NHC complexes. While the reactions in THF with AgCl or CuCl afforded anionic mono- and dicarbene complexes with solvated lithium counterions [Li(THF)_n]⁺ (n=3, 4), the reactions in toluene proceeded with elimination of LiCl and formation of the neutral phosphine and arene complexes [(WCA-NHC)M(PPh₃)] and [(WCA-NHC)M(η²-toluene)] (M=Ag, Cu). The latter were used for the preparation of chlorido- and iodido-bridged heterobimetallic Ag/Ru and Cu/Ru complexes [(WCA-NHC)M(μ-X)₂Ru(PPh₃)(η⁶-p-cymene)] (M=Ag, Cu, X=Cl; M=Ag, X=I). Surprisingly, these complexes resisted the elimination of CuCl, AgCl, or AgI, precluding WCA-NHC transmetalation.