A modular design of metal catalysts for the transfer hydrogenation of aromatic ketones

The ability of transition metal catalysts to add or remove hydrogen from organic substrates by transfer hydrogenation is a valuable synthetic tool. Towards a series of novel metal complexes with a P―NH ligand, [Ph₂PNHCH₂―C₄H₃O] derived from furfurylamine were synthesized. Reaction of [Ph₂PNHCH₂―C₄H₃O] 1 with [Ru(η⁶‐p‐cymene)(μ‐Cl)Cl]₂, [Ru(η⁶‐benzene)(μ‐Cl)Cl]₂, [Rh(μ‐Cl)(cod)]₂ and [Ir(η⁵‐C₅Me₅)(μ‐Cl)Cl]₂ gave a range of new monodentate complexes [Ru(Ph₂PNHCH₂―C₄H₃O)(η⁶‐p‐cymene)Cl₂] 2 , [Ru(Ph₂PNHCH₂―C₄H₃O)(η⁶‐benzene)Cl₂] 3 , [Rh(Ph₂PNHCH₂‐C₄H₃O)(cod)Cl] 4 , and [Ir(Ph₂PNHCH₂‐C₄H₃0)(η⁵‐C₅Me₅)Cl₂] 5 , respectively. All new complexes were fully characterized by analytical and spectroscopic methods. ³¹P‐{¹H} NMR, distortionless enhancement by polarization transfer (DEPT) or ¹H‐¹³C heteronuclear correlation (HETCOR) experiments were used to confirm the spectral assignments. Following activation by KOH, compounds 1 , 2 , 3 , 4 catalyzed the transfer hydrogenation of acetophenone derivatives to 1‐phenylethanol derivatives in the presence of iso‐PrOH as the hydrogen source. Notably [Ru(Ph₂PNHCH₂‐C₄H₃O)(η⁶‐benzene)Cl₂] 3 acts as an excellent catalyst, giving the corresponding alcohols in 98–99% yield in 20 min at 82°C (time of flight ≤ 297 h^?1) for the transfer hydrogenation reaction in comparison to analogous rhodium or iridium complexes. Copyright © 2012 John Wiley & Sons, Ltd.     

Novel cyclohexyl‐based aminophosphine ligands and use of their Ru(II) complexes in transfer hydrogenation of ketones

Two new aminophosphines – furfuryl‐(N‐dicyclohexylphosphino)amine, [Cy₂PNHCH₂–C₄H₃O] ( 1 ) and thiophene‐(N‐dicyclohexylphosphino)amine, [Cy₂PNHCH₂–C₄H₃S] ( 2 ) – were prepared by the reaction of chlorodicyclohexylphosphine with furfurylamine and thiophene‐2‐methylamine. Reaction of the aminophosphines with [Ru(η⁶‐p‐cymene)(μ‐Cl)Cl]₂ or [Ru(η⁶‐benzene)(μ‐Cl)Cl]₂ gave corresponding complexes [Ru(Cy₂PNHCH₂–C₄H₃O)(η⁶‐p‐cymene)Cl₂] ( 1a ), [Ru(Cy₂PNHCH₂–C₄H₃O)(η⁶‐benzene)Cl₂] ( 1b ), [Ru(Cy₂PNHCH₂–C₄H₃S)(η⁶‐p‐cymene)Cl₂] ( 2a ) and [Ru(Cy₂PNHCH₂–C₄H₃S)(η⁶‐benzene)Cl₂] ( 2b ), respectively, which are suitable catalyst precursors for the transfer hydrogenation of ketones. In particular, [Ru(Cy₂PNHCH₂–C₄H₃S)(η⁶‐benzene)Cl₂] acts as a good catalyst, giving the corresponding alcohols in 98–99% yield in 30 min at 82 °C (up to time of flight ≤ 588 h^?1). Copyright © 2014 John Wiley & Sons, Ltd.     

Organometallic ruthenium, rhodium and iridium complexes containing a P-bound thiophene-2-(N-diphenylphosphino)methylamine ligand: Synthesis, molecular structure and catalytic activity

Reaction of Ph₂PNHCH₂-C₄H₃S with [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂, [Ru(η⁶-benzene)(μ-Cl)Cl]₂, [Rh(μ-Cl)(cod)]₂ and [Ir(η⁵-C₅Me₅)(μ-Cl)Cl]₂ yields complexes [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-p-cymene)Cl₂], 1, [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-benzene)Cl₂], 2, [Rh(Ph₂PNHCH₂-C₄H₃S)(cod)Cl], 3 and [Ir(Ph₂PNHCH₂-C₄H₃S)(η⁵-C₅Me₅)Cl₂], 4, respectively. All complexes were isolated from the reaction solution and fully characterized by analytical and spectroscopic methods. The structure of [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-benzene)Cl₂], 2 was also determined by single crystal X-ray diffraction. 1-4 are suitable precursors forming highly active catalyst in the transfer hydrogenation of a variety of simple ketones. Notably, the catalysts obtained by using the ruthenium complexes [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-p-cymene)Cl₂], 1 and [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-benzene)Cl₂], 2 are much more active in the transfer hydrogenation converting the carbonyls to the corresponding alcohols in 98-99% yields (TOF ≤ 200 h⁻¹) in comparison to analogous rhodium and iridium complexes.     

Enantioselective transfer hydrogenation of pro-chiral ketones catalyzed by novel ruthenium and iridium complexes of well-designed phosphinite ligand

Abstract

The interaction of [Ru(η⁶-arene)(μ-Cl)Cl]₂ and Ir(η⁵-C₅Me₅)(μ-Cl)Cl]₂ with a new Ionic Liquid-based phosphinite ligand, [(Ph₂PO)-C₆H₉N₂Ph]Cl, (2) gave [Ru((Ph₂PO)-C₆H₉N₂Ph)(η⁶-p-cymene)Cl₂]Cl (3), [Ru((Ph₂PO)-C₆H₉N₂Ph)(benzene)Cl₂]Cl (4) and [Ir((Ph₂PO)-C₆H₉N₂Ph)(C₅Me₅)Cl₂]Cl (5), complexes. All the compounds were characterized by a combination of multinuclear NMR and IR spectroscopy as well as elemental analysis. Furthermore, the Ru(II) and Ir(III) catalysts were applied to asymmetric transfer hydrogenation of acetophenone derivatives using 2-propanol as a hydrogen source. The results showed that the corresponding alcohols could be obtained with good activity (up to 55% ee and 99% conversion) under mild conditions. Notably, [Ir((Ph₂PO)-C₆H₉N₂Ph)(C₅Me₅)Cl₂]Cl (5) is more active than the other analogous complexes in the transfer hydrogenation (up to 81% ee).     

Synthesis and characterization of transition metal complexes of thiophene‐2‐methylamine: X‐ray crystal structure of palladium (II) and platinum (II) complexes and use of palladium(II) complexes as pre‐catalyst in Heck and Suzuki cross‐coupling reactions

The reactions of thiophene‐2‐(N‐diphenylphosphino)methylamine, Ph₂PNHCH₂‐C₄H₃S, 1 and thiophene‐2‐[N,N‐bis(diphenylphosphino)methylamine], (Ph₂P)₂NCH₂‐C₄H₃S, 2, with MCl₂(cod) (M = Pd, Pt; cod = 1,5‐cyclooctadiene) or [Cu(CH₃CN)₄]PF₆ yields the new complexes [M(Ph₂PNHCH₂‐C₄H₃S)₂Cl₂], M = Pd 1a, Pt 1b, [Cu(Ph₂PNHCH₂‐C₄H₃S)₄]PF₆, 1c, and [M(Ph₂P)₂NCH₂‐C₄H₃S)Cl₂], M = Pd 2a, Pt 2b, {Cu[(Ph₂P)₂NCH₂‐C₄H₃S]₂}PF₆, 2c, respectively. The new compounds were isolated as analytically pure crystalline solids and characterized by ³¹P‐, ¹³C‐, ¹H‐NMR and IR spectroscopy and elemental analysis. Furthermore, the solid‐state molecular structures of representative palladium and platinum complexes of bis(phosphine)amine, 2a and 2b, respectively, were determined using single crystal X‐ray diffraction analysis. The palladium complexes were tested as potential catalysts in the Heck and Suzuki cross‐coupling reactions. Copyright © 2009 John Wiley & Sons, Ltd.     

Improved Synthesis of the [Ru(η6‐p‐cymene)Cl3] Anion: Facile Isolation under Mild Conditions

Reaction of [Ru(η⁶‐p‐cymene)Cl₂]₂ with two equivalents of [Ph₄P][Cl] in CH₂Cl₂ yields [Ph₄P][Ru(η⁶‐p‐cymene)Cl₃], containing a trichlororuthenate(II) anion. In solution, an equilibrium between the product and [Ru(η⁶‐p‐cymene)Cl₂]₂ is observed, which in CDCl₃ is nearly completely shifted to the dimer, whereas in CD₂Cl₂ essentially a 1:1‐mixture of the two ruthenium species is present. Crystallization from CH₂Cl₂/pentane yielded two different crystals, which were identified by X‐ray analysis as [Ph₄P][Ru(η⁶‐p‐cymene)Cl₃] and [Ph₄P][Ru(η⁶‐p‐cymene)Cl₃]·CH₂Cl₂.     

Ruthenium complexes of aminophosphine ligands and their use as pre-catalysts in the transfer hydrogenation of aromatic ketones: X-ray crystal structure of thiophene-2-(N-diphenylthiophosphino)methylamine

Reaction of thiophene-2-methylamine with one or two equivalents of PPh₂Cl in the presence of NEt₃, proceeds in thf to give thiophene-2-(N-diphenylphosphino)methylamine, 1a and thiophene-2-(N,N-bis(diphenylphosphino))methylamine, 2a respectively, under anaerobic conditions. Oxidations of 1a and 2a with aqueous hydrogen peroxide, elemental sulfur or gray selenium in thf gives the corresponding oxides, sulfides and selenides [Ph₂P(E)NHCH₂-C₄H₃S] (E: O 1b, S 1c, Se 1d) and [(Ph₂P(E))₂NCH₂-C₄H₃S], (E: O 2b, S 2c, Se 2d) respectively, in high yield. Furthermore, two novel Ru(II) complexes with the P-N ligands 1a and 2a were synthesized starting with the complex [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂. The complexes were fully characterized by analytical and spectroscopic methods. ³¹P-{¹H} NMR, DEPT, ¹H-¹³C HETCOR or ¹H-¹H COSY correlation experiments were used to confirm the spectral assignments. The molecular structure of thiophene-2-(N-diphenylthiophosphino)methylamine was also elucidated by single-crystal X-ray crystallography. Following activation by NaOH, compounds 3 and 4 catalyze the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of iso-PrOH as the hydrogen source. [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-p-cymene)Cl₂], 3 and [Ru((PPh₂)₂NCH₂-C₄H₃S)(η⁶-p-cymene)Cl]Cl, 4 complexes are suitable catalyst precursors for the transfer hydrogenation of acetophenone derivatives in 0.1 M iso-PrOH solution. Notably 4 acts as an excellent catalyst giving the corresponding alcohols in excellent conversions up to 99% (TOF ? 744 h⁻¹). This transfer hydrogenation is characterized by low reversibility under the experimental conditions.     

Microwave‐Assisted Synthesis and Transformations of Cationic CpRu(II)(naphthalene) and CpRu(II)(naphthoquinone) Complexes

Details of the direct synthesis of cationic Ru(II)(η⁵‐Cp)(η⁶‐arene) complexes from ruthenocene using microwave heating are reported. Developed for the important catalyst precursor [Ru(II)(η⁵‐Cp)(η⁶‐1‐4,4a,8a‐naphthalene)][PF₆] reaction time could be shortened from three days to 15 min. The method was extended to [Ru(II)(η⁶‐benzene)(η⁵‐Cp)][PF₆], [Ru(II)(η⁵‐Cp)(η⁶‐toluene)][PF₆], [Ru(II)(η⁵‐Cp)(η⁶‐mesitylene)][PF₆], [Ru(II)(η⁵‐Cp)(η⁶‐hexamethylbenzene)][PF₆], [Ru(II)(η⁵Cp)(η⁶‐indane)][PF₆], [Ru(II)(η⁵‐Cp)(η⁶‐2,6‐dimethylnaphthalene)][PF₆], and [Ru(II)(η⁵‐Cp)(η⁶‐pyrene)][PF₆]. 1‐methylnaphthalene and 2,3‐dimethylnaphthalene afforded mixtures of regioisomeric complexes. [Ru(Cp)(CH₃CN)₃][PF₆], derived from the naphthalene precursor provided access to the cationic RuCp complexes of naphthoquinone, tetralindione, 1,4‐dihydroxynaphthalene, and 1,4‐dimethoxynaphthalene. Reduction of the tetralindione complex afforded selectively the endo,endo diol derivative. X‐Ray structures of five complexes are reported.     

The synthesis of new paracyclophane complexes of ruthenium(II): Crystal structure of [Ru(η6-C16H16)Cl(C5H5N)2][PF6]

The dimer [Ru(η⁶-C₁₆H₁₆)Cl₂]₂ reacts with ligands L (L  PMe₂Ph, PPh₃, C₅H₅N) to give both neutral monomeric [Ru(η⁶-C₁₆H₁₆)Cl₂L] and cationic monomeric [Ru(η⁶-C₁₆H₁₆)ClL₂]⁺ products. One example, [Ru(η⁶-C₁₆H₁₆)Cl(C₅H₅N)₂]-[PF₆], has been characterised by X-ray crystallography. Reaction with the bidentate ligand 2,2′-bipyridyl gives the mononuclear cation [Ru(η⁶-C₁₆H₁₆)Cl(bipy)]⁺, isolated as its [BPh₄]⁻ salt, whereas reaction with OMe⁻ or OEt⁻ gives dinuclear products [Ru(η⁶-C₁₆H₁₆)₂(OR)₃]⁺.     

New active ruthenium(II) complexes based N3,N3′-bis(diphenylphosphino)-2,2′-bipyridine-3,3′-diamine and P,P′-diphenylphosphinous acid-P,P′-[2,2′-bipyridine]-3,3′-diyl ester ligands for transfer hydrogenation of aromatic ketones by propan-2-ol

The dimeric starting material [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂ reacts with N3,N3′-bis(diphenylphosphino)-2,2′-bipyridine-3,3′-diamine, 1 and P,P′-diphenylphosphinous acid-P,P′-[2,2′-bipyridine]-3,3′-diyl ester, 2 ligands to afford bridged dinuclear complexes [C₁₀H₆N₂{NHPPh₂-Ru(η⁶-p-cymene)Cl₂}₂], 3 and [C₁₀H₆N₂{OPPh₂-Ru(η⁶-p-cymene)Cl₂}₂], 4 in quantitative yields. These bis(aminophosphine) and bis(phosphinite) based Ru(II) complexes serve as active catalyst precursors for the transfer hydrogenation of acetophenone derivatives in 2-propanol and especially 4 acts as a good catalyst, giving the corresponding alcohols in 99% yield in 20 min (TOF ? 280 h⁻¹).     

Synthesis and structural characterization of ruthenium(II) and iron(II) complexes containing 1,2-di-(2-thienyl)-ethene derived ligands as chromophores

A new family of three-legged piano stool structured organometallic compounds containing the η⁵-cyclopentadienylruthenium(II)/iron(II) fragments {M(η⁵-C₅H₅) (DPPE)}⁺, {Ru(η⁵-C₅H₅)(PPh₃)₂}⁺ and {Ru(η⁵-C₅H₅)(TMEDA)}⁺ with coordinated thiophene based chromophores, namely 5-(2-thiophen-2-yl-vinyl)-thiophene-2-carbonitrile (L1) and 5-[2-(5-Nitro-thiophen-2-yl)-vinyl]-thiophene-2-carbonitrile (L2) has been synthesized and fully characterized by ¹H, ¹³C, ³¹P NMR, IR and UV-Vis spectroscopies. Also, electrochemical studies were carried out by cyclic voltammetry and all experimental data are interpreted and compared with related compounds under the scope of NLO properties. Compounds [Ru(η⁵-C₅H₅)(DPPE)(NC(C₄H₂S)C(H)C(H)(C₄H₃S))][CF₃SO₃] (1′Ru) [Fe(η⁵-C₅H₅)(DPPE)(NC(C₄H₂S)C(H)C(H)(C₄H₃S))] [PF₆] (1Fe) and [Ru(η⁵-C₅H₅)(DPPE)(NC(C₄H₂S)C(H)C(H)(C₄H₂S)NO₂)][CF₃SO₃] (4′Ru) were also crystallographically characterized.     

Dicarbollide complexes of rhodium and ruthenium

The 7,8-B₉C₂H₁₁^2- ion reacts with (Ph₃P)₂Rh(CO)Cl to form (B₉C₂H₁₁)-Rh(Cl)(Ph₃P)₂. This rhodacarborane reacts with NaBPh₄ to produce (B₉C₂H₁₁-Rh(Ph₃P)(Ph₄B). The new metallocarboranes [(B₉C₂H₁₁)Rh(Ph₃P)(C₆H₆)]₂ and (B₉C₂H₁₁)Rh(H)(Ph₃P) were obtained from the reaction of B₉C₂H₁₁^2- and (Ph₃P)₃RhCl. The ruthenacarboranes (B₉C₂H₁₁)Ru(CO)(Ph₃P)₂ and (B₉C₂H₁₁-Ru(CO)₃ · 0.5C₆H₆ were prepared from (Ph₃P)Ru(CO)₂Cl₂ and [Ru(CO)₃Cl₂]₂ respectively.     

Conversion of allene into μ-dimethylcarbene at a diruthenium centre

Treatment of [Ru₂(CO)(μ-CO) {μ-C(O)C₂Ph₂} (η-C ₅H₅)₂] with allene in toluene at 100°C displaces diphenylacetylene and produces [Ru(CO)(η-C₅H₅)-{η³-C₃H₄Ru(CO)₂(η-C₅H₅)}]; upon protonation a 1-methylvinyl cation [Ru₂(CO)₂(μ-CO){μ-C(Me)CH₂}(η-C₅H₅)₂]⁺ is formed which undergoes nucleophillic attack by hydride to yield the μ-dimethylcarbene complex [Ru₂(CO)₂-(μ-CO)(μ-CMe₂)(η-C₅H₅)₂].     

Reactions of [Cp*Ru(H2O)(NBD)]+ with alkynes

Formal [2 + 2 + 2] addition reactions of [Cp*Ru(H₂O)(NBD)]BF₄ (NBD = norbornadiene) with PhC?CR (R = H, COOEt) give [Cp*Ru(η⁶‐C₆H₅? C₉H₈R)] BF₄ (1a, R = H; 2a, R = COOEt). Treatment of [Cp*Ru(H₂O)(NBD)]BF₄ with PhC?C? C?CPh does not give [2 + 2 + 2] addition product, but [Cp*Ru(η⁶‐C₆H₅? C?C? C?CPh)] BF₄(3a). Treatment of 1a, 2a, 3a with NaBPh₄ affords [Cp*Ru(η⁶‐C₆H₅? C₉H₈R)] BPh₄ (1b, R = H; 2b, R = COOEt) and [Cp*Ru(η⁶‐C₆H₅? C?C? C?CPh)] BPh₄(3b). The structures of 1b, 2b and 3b were determined by X‐ray crystallography. Copyright © 2007 John Wiley & Sons, Ltd.     

Hydrogenation of Aromatics with [Ru(η 5-C5H5)Cl(TPPDS)2] in Biphasic Medium

[Ru(η⁵-C₅H₅)Cl(TPPDS)₂], [TPPDS=P(C₆H₅)(C₆H₄SO₃⁻)₂] in biphasic (n-heptane/water) medium hydrogenates toluene, benzene and m-xylene (105 °C, 1400 psig H₂, substrate/catalyst=600:1, 4 h) and in toluene hydrogenation gives methylcyclohexane. Catalytic activity increases with temperature, H₂ pressure, ionic strength, and pH lower than 10. The catalytic water solution can be reused several times with little activity loss.     

Preparation and Reactivity of Mo(NCMe)(η2‐C2Ph2)2(η4‐C4Ph4)

Reaction of Mo(CO)(η²‐C₂Ph₂)₂(η⁴‐C₄Ph₄) and Me₃NO in acetonitrile solvent affords Mo(NCMe)(η²‐C₂Ph₂)₂(η⁴‐C₄Ph₄) 1 . Compound 1 reacts with trimethylphosphine to produce Mo(PMe₃)(η²‐C₂Ph₂)₂(η⁴‐C₄Ph₄) 2 , or reacts with diphenylacetylene to produce (η⁵‐C₅Ph₅)₂Mo 3 and Mo(η²‐O₂CPh)(η⁴‐C₄Ph₄H)(η⁴‐C₄Ph₄) 4 . The molecular structures of 1, 2 and 4 have been determined by an X‐ray diffraction study.     

Acetylene Dithiolate Linking up the [Tp′W(CO)(CN)] Moiety with RuII or PdII

A series of heterodinuclear complexes with acetylene dithiolate (acdt^2?) as the bridging moiety were synthesised by a facile one‐pot procedure that avoided use of the highly elusive acetylene dithiol. Generation of the W–Ru complex [Tp′W(CN)(CO)(C₂S₂)Ru(η⁵‐C₅H₅)(PPh₃)] (Tp’=hydrotris(3,5‐dimethylpyrazolyl)borate) and the W–Pd complexes [Tp′W(CN)(CO)(C₂S₂)Pd(dppe)] and [Tp′W(CO)₂(C₂S₂)Pd(dppe)][PF₆] (dppe=1,2‐bis(diphenylphoshino)ethane), which exhibit a [W(η²‐κ²‐C₂S₂)M] core (M=Ru, Pd), was accomplished by using a transition‐metal‐assisted solvolytical removal of the Me₃Si‐ethyl thiol protecting groups. All intermediate species of the reaction have been fully characterised. The highly coloured W–Ru complex [Tp′W(CN)(CO)(C₂S₂)Ru(η⁵‐C₅H₅)(PPh₃)] shows reversible redox chemistry, as does the prototype complex [Tp′W(CO)₂(C₂S₂)Ru(η⁵‐C₅H₅)(PPh₃)][PF₆]. Single crystal X‐ray diffraction and IR, EPR and UV/Vis spectroscopic studies in conjunction with DFT calculations prove the high electronic delocalisation of states over the acdt^2? linker. Comparative studies revealed a higher donor strength and more pronounced dithiolate character of acdt^2? in [Tp′W(CN)(CO)(C₂S₂)Ru(η⁵‐C₅H₅)(PPh₃)] relative to [Tp′W(CO)₂(C₂S₂)Ru(η⁵‐C₅H₅)(PPh₃)]⁺. In addition, the influence of the overall complex charge on the metric parameters was investigated by single‐crystal X‐ray diffraction studies with the W–Pd complexes [Tp′WL₂(C₂S₂)Pd(dppe)] (L=(CN^?)(CO) or (CO)₂). The central [W(C₂S₂)Pd] units exhibit high structural similarity, which indicates the extensive delocalisation of charge over both metals.     

Influence of Cyclopentadienyl Ring‐Tilt on Electron‐Transfer Reactions: Redox‐Induced Reactivity of Strained [2] and [3]Ruthenocenophanes

In contrast to ruthenocene [Ru(η⁵‐C₅H₅)₂] and dimethylruthenocene [Ru(η⁵‐C₅H₄Me)₂] ( 7 ), chemical oxidation of highly strained, ring‐tilted [2]ruthenocenophane [Ru(η⁵‐C₅H₄)₂(CH₂)₂] ( 5 ) and slightly strained [3]ruthenocenophane [Ru(η⁵‐C₅H₄)₂(CH₂)₃] ( 6 ) with cationic oxidants containing the non‐coordinating [B(C₆F₅)₄]^? anion was found to afford stable and isolable metal?metal bonded dicationic dimer salts [Ru(η⁵‐C₅H₄)₂(CH₂)₂]₂[B(C₆F₅)₄]₂ ( 8 ) and [Ru(η⁵‐C₅H₄)₂(CH₂)₃]₂[B(C₆F₅)₄]₂ ( 17 ), respectively. Cyclic voltammetry and DFT studies indicated that the oxidation potential, propensity for dimerization, and strength of the resulting Ru?Ru bond is strongly dependent on the degree of tilt present in 5 and 6 and thereby degree of exposure of the Ru center. Cleavage of the Ru?Ru bond in 8 was achieved through reaction with the radical source [(CH₃)₂NC(S)S?SC(S)N(CH₃)₂] (thiram), affording unusual dimer [(CH₃)₂NCS₂Ru(η⁵‐C₅H₄)(η³‐C₅H₄)C₂H₄]₂[B(C₆F₅)₄]₂ ( 9 ) through a haptotropic η⁵–η³ ring‐slippage followed by an apparent [2+2] cyclodimerization of the cyclopentadienyl ligand. Analogs of possible intermediates in the reaction pathway [C₆H₅ERu(η⁵‐C₅H₄)₂C₂H₄][B(C₆F₅)₄] [E=S ( 15 ) or Se ( 16 )] were synthesized through reaction of 8 with C₆H₅E?EC₆H₅ (E=S or Se).     

A mixed chloride/trifluoromethanesulfonate ligand species in a ruthenium(II) complex

The compound [2‐(aminomethyl)pyridine‐κ²N,N′][chlorido/trifluoromethanesulfonato(0.91/0.09)][(10,11‐η)‐5H‐dibenzo[a,d]cyclohepten‐5‐amine‐κN](triphenylphosphane‐κP)ruthenium(II) trifluoromethanesulfonate dichloromethane 0.91‐solvate, [Ru(CF₃SO₃)_0.09Cl_0.91(C₆H₈N₂)(C₁₅H₁₃N)(C₁₈H₁₅P)]CF₃SO₃·0.91CH₂Cl₂, belongs to a series of Ru^II complexes that had been tested for transfer hydrogenation, hydrogenation of polar bonds and catalytic transfer hydrogenation. The crystal structure determination of this complex revealed disorder in the form of two different anionic ligands sharing the same coordination site, which other spectroscopic methods failed to characterize. The reduced catalytic activity of the title compound was not fully understood until the crystallographic data provided evidence for the mixed ligand species. The crystal structure clearly shows that the majority of the synthesized material has a chloride ligand present. Only a small portion of the material is the expected complex [Ru^II(OTf)(ampy)(η²‐tropNH₂)(PPh₃)]OTf, where OTf is triflate or trifluoromethanesulfonate, ampy is 2‐(aminomethyl)pyridine and tropNH₂ is 5H‐dibenzo[a,d]cyclohepten‐5‐amine.     

Chiral η6‐Arene/N‐Tosylethylenediamine–Ruthenium(II) Complexes: Solution Behavior and Catalytic Activity for Asymmetric Hydrogenation

Aromatic ketones are enantioseletively hydrogenated in alcohols containing [RuX{(S,S)‐Tsdpen}(η⁶‐p‐cymene)] (Tsdpen=TsNCH(C₆H₅)CH(C₆H₅)NH₂; X=TfO, Cl) as precatalysts. The corresponding Ru hydride (X=H) acts as a reducing species. The solution structures and complete spectral assignment of these complexes have been determined using 2D NMR (¹H‐¹H DQF‐COSY, ¹H‐¹³C HMQC, ¹H‐¹⁵N HSQC, and ¹H‐¹⁹F HOESY). Depending on the nature of the solvents and conditions, the precatalysts exist as a covalently bound complex, tight ion pair of [Ru⁺(Tsdpen)(cymene)] and X^?, solvent‐separated ion pair, or discrete free ions. Solvent effects on the NH₂ chemical shifts of the Ru complexes and the hydrodynamic radius and volume of the Ru⁺ and TfO^? ions elucidate the process of precatalyst activation for hydrogenation. Most notably, the Ru triflate possessing a high ionizability, substantiated by cyclic voltammetry, exists in alcoholic solvents largely as a solvent‐separated ion pair and/or free ions. Accordingly, its diffusion‐derived data in CD₃OD reflect the independent motion of [Ru⁺(Tsdpen)(cymene)] and TfO^?. In CDCl₃, the complex largely retains the covalent structure showing similar diffusion data for the cation and anion. The Ru triflate and chloride show similar but distinct solution behavior in various solvents. Conductivity measurements and catalytic behavior demonstrate that both complexes ionize in CH₃OH to generate a common [Ru⁺(Tsdpen)(cymene)] and X^?, although the extent is significantly greater for X=TfO^?. The activation of [RuX(Tsdpen)(cymene)] during catalytic hydrogenation in alcoholic solvent occurs by simple ionization to generate [Ru⁺(Tsdpen)(cymene)]. The catalytic activity is thus significantly influenced by the reaction conditions.