Asymmetric Transfer Hydrogenation of Arylketones Catalyzed by Enantiopure Ruthenium(II)/Pybox Complexes Containing Achiral Phosphonite and Phosphinite Ligands.

A family of complexes of the formula -[RuCl(L)(R-pybox)] (R-pybox = (,)-Pr-pybox, (,)-Ph-pybox, L = monodentate phosphonite, PPh(OR), and phosphinite, L = PPh(OR), ligands) were screened in the catalytic asymmetric transfer hydrogenation of acetophenone, observing a strong influence of the nature of both the R-pybox substituents and the L ligand in the process. The best results were obtained with complex -[RuCl{PPh(OEt)}{(,)-Ph-pybox}] (), which provided high conversion and enantioselectivity (up to 96% enantiomeric excess, ) for the reduction of a variety of aromatic ketones, affording the ()-benzylalcohols.

σ-Silane Platinum(II) Complexes as Intermediates in C-Si Bond-Coupling Processes.

Platinum complexes [Pt(NHC')(NHC)][BAr ] (in which NHC' denotes a cyclometalated N-heterocyclic carbene ligand, NHC) react with primary silanes RSiH to afford the cyclometalated platinum(II) silyl complexes [Pt(NHC-SiHR')(NHC)][BAr ] through a process that involves the formation of C-Si and Pt-Si bonds with concomitant extrusion of H . Low-temperature NMR studies indicate that the process proceeds through initial formation of the σ-SiH complexes [Pt(NHC')(NHC)(HSiH R)][BAr ], which are stable at temperatures below -10 °C. At higher temperatures, activation of one Si-H bond followed by a C-Si coupling reaction generates an agostic SiH platinum hydride derivative [Pt(H)(NHC'-SiH R)(NHC)][BAr ], which undergoes a second Si-H bond activation to afford the final products.

Isolation of a Cationic Platinum(II) σ-Silane Complex.

The platinum complex [Pt(I Bu Pr')(I Bu Pr)][BAr ] interacts with tertiary silanes to form stable (<0 °C) mononuclear Pt σ-SiH complexes [Pt(I Bu Pr')(I Bu Pr)(η -HSiR )][BAr ]. These compounds have been fully characterized, including X-ray diffraction methods, as the first examples for platinum. DFT calculations (including electronic topological analysis) support the interpretation of the coordination as an unusual η -SiH.

Cationic Platinum(II) σ-SiH Complexes in Carbon Dioxide Hydrosilation.

The low-electron-count cationic platinum complex [Pt(ItBu')(ItBu)][BAr ], 1, interacts with primary and secondary silanes to form the corresponding σ-SiH complexes. According to DFT calculations, the most stable coordination mode is the uncommon η -SiH. The reaction of 1 with Et SiH leads to the X-ray structurally characterized 14-electron Pt species [Pt(SiEt H)(ItBu) ][BAr ], 2, which is stabilized by an agostic interaction.

Synthesis of Silver(I) and Gold(I) Complexes Containing Enantiopure Pybox Ligands. First Assays on the Silver(I)-Catalyzed Asymmetric Addition of Alkynes to Imines.

Dinuclear complexes [Ag2(CF3SO3){(S,S)-(i)Pr-pybox}2][CF3SO3] (1), [Ag2(R-pybox)2][X]2 [R-pybox = 2,6-bis[4-(S)-isopropyloxazolin-2-yl]pyridine (S,S)-(i)Pr-pybox and X = PF6 (2) and BF4 (3); R-pybox = 2,6-bis[(3aS,8aR)-8,8a-dihydro-3aH-indeno[1,2-d]oxazol-2-yl]pyridine (3aS,3a'S,8aR,8a'R)-indane-pybox and X = CF3SO3 (4)], [Ag2{(S,S)-(i)Pr-pybox}{(3aS,3a'S,8aR,8a'R)-indane-pybox}][CF3SO3]2 (5), and [Ag2(R-pybox)3][X]2 [R-pybox = (3aS,3a'S,8aR,8a'R)-indane-pybox and X = CF3SO3 (10), SF6 (11), and PF6 (12)] as well as mononuclear complexes [Ag(R-pybox)2][X] [R-pybox = (S,S)-(i)Pr-pybox and X = SbF6 (6), PF6 (7), and BF4 (8); R-pybox = (3aS,3a'S,8aR,8a'R)-indane-pybox) and X = BF4 (9)] have been prepared by the reaction of the corresponding silver salts and pybox ligands using the appropriate molar ratio conditions. The first gold(I)/pybox complex [Au6Cl4{(S,S)-(i)Pr-pybox}4][AuCl2]2 (13) has been synthesized by the reaction of [AuCl{S(CH3)2}] and (S,S)-(i)Pr-pybox (1:1 molar ratio) in acetonitrile. The structures of the dinuclear (1, 4, 5, 10, and 11) and mononuclear (6 and 9) silver complexes and the hexanuclear gold complex 13 have been determined by single-crystal X-ray diffraction analysis.

Catalytic dehydrocoupling of amine-boranes and amines into diaminoboranes: isolation of a Pt(ii), Shimoi-type, η(1)-BH complex.

The platinum complex [Pt(I(t)Bu')(I(t)Bu)][BAr(F)] is a very efficient catalyst in the synthesis of diaminoboranes through dehydrocoupling of amine-boranes and amines. Shimoi-type, η(1)-BH complexes are key intermediates in the process.

Introducing deep eutectic solvents as biorenewable media for Au(I)-catalysed cycloisomerisation of γ-alkynoic acids: an unprecedented catalytic system.

Cycloisomerisation of γ-alkynoic acids into cyclic enol-lactones was conveniently performed, for the first time, in the eutectic mixture 1ChCl/2Urea under standard bench experimental conditions (at room temperature, under air and in the absence of co-catalysts) by using a new iminophosphorane-Au(I) complex as the catalyst. Furthermore, the catalytic system could be recycled up to four runs.

An efficient ruthenium(IV) catalyst for the selective hydration of nitriles to amides in water under mild conditions.

A Ru(IV) catalyst able to promote the selective hydration of nitriles to amides in water, at low metal loadings and under mild conditions, is presented.

A stable, mononuclear, cationic Pt(III) complex stabilised by bulky N-heterocyclic carbenes.

The thermally stable, paramagnetic Pt(iii) complex [PtI2(IPr)2][BAr(F)] has been prepared by oxidation of the Pt(ii) complex [PtI2(IPr)2] with iodine in the presence of NaBAr(F). X-ray crystallographic studies revealed the mononuclear nature of this species with a square-planar geometry. EPR and DFT studies pointed out to a metal-centred radical.

Antitumor activity of new enantiopure pybox-ruthenium complexes.

New ruthenium complexes containing enantiopure 2,6-bis[4'(R)-phenyloxazolin-2'-il-pyridine] ((R,R)-Ph-pybox), 2,6-bis[4'(S)-isopropyloxazolin-2'-il-pyridine] ((S,S)-(i)Pr-pybox) or 2,6-bis[4'(R)-isopropyloxazolin-2'-il-pyridine] ((R,R)-(i)Pr-pybox) and water soluble 1,3,5-triaza-7-phosphaadamantane (PTA) or N-substituted PTA phosphanes have been synthesized in high yields and fully characterized. The interactions of these compounds with plasmidic DNA and their cytotoxic activity against the human cervical cancer HeLa cell line are reported, pointing out for the first time the different behaviour of ruthenium enantiomers affecting the cell cycle in HeLa tumor cells.

Archaeological, radiological, and biological evidence offer insight into Inca child sacrifice.

Examination of three frozen bodies, a 13-y-old girl and a girl and boy aged 4 to 5 y, separately entombed near the Andean summit of Volcán Llullaillaco, Argentina, sheds new light on human sacrifice as a central part of the Imperial Inca capacocha rite, described by chroniclers writing after the Spanish conquest. The high-resolution diachronic data presented here, obtained directly from scalp hair, implies escalating coca and alcohol ingestion in the lead-up to death. These data, combined with archaeological and radiological evidence, deepen our understanding of the circumstances and context of final placement on the mountain top.

New Ag(I)-iminophosphorane coordination polymers as efficient catalysts precursors for the MW-assisted Meyer-Schuster rearrangement of propargylic alcohols in water.

Treatment of the N-thiophosphorylated iminophosphorane ligands (PTA)═NP(═S)(OR)2 [PTA = 1,3,5-triaza-7-phosphaadamantane, 3a and 3b] and (DAPTA)═NP(═S)(OR)2 [DAPTA = 3,7-diacetyl-1,3,7-triaza-5-bicyclo[3.3.1]nonane, 4a and 4b] with an equimolecular amount of AgSbF6 leads to high-yield formation of the new one-dimensional coordination polymers [Ag{μ(2)-N,S-(PTA)═NP(═S)(OR)2}]x[SbF6]x (5a and 5b) and [Ag{μ(2)-O,S-(DAPTA)═NP(═S)(OR)2}]x[SbF6]x (6a and 6b), respectively.

Synthesis and reactivity of new rhenium(I) complexes containing iminophosphorane-phosphine ligands: application to the catalytic isomerization of propargylic alcohols in ionic liquids.

[ReBr(CO)5] reacts with the iminophosphorane-phosphine ligands Ph2PCH2P(═NR)Ph2 (R = P(═O)(OEt)2 (1a), P(═O)(OPh)2 (1b), P(═S)(OEt)2 (1c), P(═S)(OPh)2 (1d), 4-C6F4CHO (1e), 4-C6F4CN (1f), 4-C5F4N (1g)) affording the neutral complexes [ReBr(κ(2)-P,X-Ph2PCH2P{═NP(═X)(OR)2}Ph2)(CO)3] (X = O, R = Et (2a), Ph (2b); X = S, R = Et (2c), Ph (2d)) and [ReBr{κ(2)-P,N-Ph2PCH2P(═NR)Ph2}(CO)3] (R = P(═O)(OEt)2 (3a), P(═O)(OPh)2 (3b), 4-C6F4CHO (3e), 4-C6F4CN (3f), 4-C5F4N (3g)). The reactivity of the cationic complex [Re(κ(3)-P,N,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3][SbF6] (4d) has been explored allowing the synthesis of the cationic [Re(L)(κ(2)-P,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3][SbF6] (L = acetone (5a), CH3C≡N (5b), pyridine (5c), PPh3 (5d)) and the neutral [ReY(κ(2)-P,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3] (Y = Cl (6a), I (6b), N3 (6c)) complexes. The catalytic activity of complex 4d in the regioselective isomerization of terminal propargylic alcohols HC≡CCR(1)R(2)(OH) into α,β-unsaturated aldehydes R(1)R(2)C═CHCHO or ketones R(3)R(4)C═CR(1)COMe (if R(2) = CHR(3)R(4)) under neutral conditions in ionic liquids has being studied.

Functionalized arene-ruthenium(II) complexes: dangling vs. tethering side chain.

The reactivity of compounds [RuCl2(η(6)-C6H5OCH2CH2OH)(L)] (L = phosphine or phosphite) towards the chloride abstractor AgSbF6 has been investigated. Thus, the treatment of the triphenylphosphite complex [RuCl2(η(6)-C6H5OCH2CH2OH){P(OPh)3}] with one equivalent of AgSbF6 gave rise to the formation of the dinuclear dichloro-bridged species [{Ru(μ-Cl)(η(6)-C6H5OCH2CH2OH){P(OPh)3}}2](2+) as the hexafluoroantimonate salt. On the other hand, the triphenylphosphine analog [RuCl2(η(6)-C6H5OCH2CH2OH)(PPh3)] led, under the same experimental conditions, to the di-ruthenium derivative [{RuCl(η(6)-C6H5OCH2CH2OH)(PPh3)}2(μ-Cl)][SbF6] containing only one Cl-bridge.

Characterization of a paramagnetic, mononuclear Pt(III)-alkyl complex intermediate in carbon-halogen bond coupling reactions.

Addition of Br(2) or I(2) to 14-electron, cationic Pt(II)-alkyl complexes led to the formation of the corresponding carbon-halogen Pt(II) coupling products. Low temperature experiments with Br(2) allowed us to isolate and characterize crystallographically a very unusual mononuclear, paramagnetic Pt(III)-alkyl intermediate with a seesaw structure that can be further oxidized to a transient Pt(IV) species before reductive carbon-halogen coupling reaction takes place.

Highly efficient redox isomerisation of allylic alcohols catalysed by pyrazole-based ruthenium(IV) complexes in water: mechanisms of bifunctional catalysis in water.

The catalytic activity of ruthenium(IV) ([Ru(η(3):η(3)-C(10)H(16))Cl(2)L]; C(10)H(16) = 2,7-dimethylocta-2,6-diene-1,8-diyl, L = pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, 3-methyl-5-phenylpyrazole, 2-(1H-pyrazol-3-yl)phenol or indazole) and ruthenium(II) complexes ([Ru(η(6)-arene)Cl(2)(3,5-dimethylpyrazole)]; arene = C(6)H(6), p-cymene or C(6)Me(6)) in the redox isomerisation of allylic alcohols into carbonyl compounds in water is reported. The former show much higher catalytic activity than ruthenium(II) complexes. In particular, a variety of allylic alcohols have been quantitatively isomerised by using [Ru(η(3):η(3)-C(10)H(16))Cl(2)(pyrazole)] as a catalyst; the reactions proceeded faster in water than in THF, and in the absence of base.

Cycloisomerization versus hydration reactions in aqueous media: a Au(III)-NHC catalyst that makes the difference.

A novel water-soluble Au(III)-NHC complex has been synthesized and successfully applied in the intramolecular cyclization of γ-alkynoic acids into enol-lactones under biphasic toluene/water conditions, thus representing a rare example of an active and selective catalyst for this transformation in aqueous media. Remarkably, competing alkyne hydration processes were not observed, even during the desymmetrization reaction of challenging 1,6-diyne substrates. In addition, after phase separation, the water-soluble Au(III) catalyst could be recycled 10 times without loss of activity or selectivity.

Tuning N-heterocyclic carbenes in T-shaped Pt(II) complexes for intermolecular C-H bond activation of arenes.

Small change matters: T-shaped Pt(II) complexes with less flexible substituents, than, for example, isopropyl or tert-butyl groups, on N-heterocyclic carbene (NHC) ligands allow for C-H bond activation reactions of aromatic compounds (see scheme; BAr(f)(4)(-) =tetrakis[(3,5-trifluoromethyl)phenyl]borate; F yellow, Pt red). NHC substituents that are not highly branched prevent agostic interactions and reduce the barriers to achieve the C-H bond cleavage.

Expeditious entry to novel 2-methylene-2,3-dihydrofuro[3,2-c] chromen-2-ones from 6-chloro-4-hydroxychromen-2-one and propargylic alcohols.

A catalytic system consisting of the ruthenium(II) complex [Ru(η³-2-C3H4Me)(CO)(dppf)][SbF6] (dppf=1,1'-bis(diphenylphosphino)ferrocene) and trifluoroacetic acid has been used to promote the coupling of secondary propargylic alcohols with 6-chloro-4-hydroxychromen-2-one. The reactions afforded unusual 2-methylene-2,3-dihydrofuro[3,2-c]chromen-2-ones in good yields.

Access to unusual polycyclic spiro-enones from 2,2'-bis(allyloxy)-1,1'-binaphthyls using Grubbs' catalysts: an unprecedented one-pot RCM/Claisen sequence.

Treatment of 2,2'-bis(allyloxy)-1,1'-binaphthyls with the first-generation Grubbs' carbene under MW-irradiation results in the formation of new polycyclic spiro-enones through an unprecedented RCM/Claisen sequence.

Synthesis and structure of ruthenium(IV) complexes featuring N-heterocyclic ligands with an N-H group as the hydrogen-bond donor: hydrogen interactions in solution and in the solid state.

The synthesis and characterization of novel ruthenium(IV) complexes [Ru(η(3):η(3)-C(10)H(16))Cl(2)L] [L = 3-methylpyrazole (2b), 3,5-dimethylpyrazole (2c), 3-methyl-5-phenylpyrazole (2d), 2-(1H-pyrazol-5-yl)phenol (2e), 6-azauracile (3), and 1H-indazol-3-ol (4)] are reported. Complex 2e is converted to the chelated complex [Ru(η(3):η(3)-C(10)H(16))Cl(κ(2)-N,O-2-(1H-pyrazol-3-yl)phenoxy)] (5) by treatment with an excess of NaOH. All of the ligands feature N-H, O-H, or C═O as the potential hydrogen-bonding group.

Novel rhenium(I) catalysts for the isomerization of propargylic alcohols into α,β-unsaturated carbonyl compounds: an unprecedented recyclable catalytic system in ionic liquids.

Carbonyl rhenium(I) complexes are efficient catalysts for the regioselective isomerization of terminal propargylic alcohols into α,β-unsaturated aldehydes or ketones which can be used as an unprecedented recyclable catalytic system (up to 10 consecutive runs) in the ionic liquid [BMIM][PF(6)].

A simple, general route to 2-pyridylidene transition metal complexes.

Pyridinium 2-carboxylates decompose thermally in the presence of a variety of late transition metal precursors to yield the corresponding 2-pyridylidene-like complexes. The mild reaction conditions and structural diversity that can be generated in the heterocyclic ring make this method an attractive alternative for the synthesis of 2-pyridylidene complexes. IR spectra of the Ir(i) carbonyl compounds [IrCl(NHC)(CO)(2)] indicate that these N-heterocyclic carbene ligands are among the strongest σ-electron donors.

Antitumor activity of new hydridotris(pyrazolyl)borate ruthenium(II) complexes containing the phosphanes PTA and 1-CH3-PTA.

The synthesis and full characterization of new half-sandwich ruthenium(II) complexes containing κ(3)(N,N,N)-hydridotris(pyrazolyl)borate (κ(3)(N,N,N)-Tp) and the water-soluble phosphanes 1,3,5-triaza-7-phosphatricyclo[3.3.1.

Chiral phosphonite, phosphite and phosphoramidite eta6-arene-ruthenium(II) complexes: application to the kinetic resolution of allylic alcohols.

The synthesis and characterization of chiral arene-ruthenium complexes [RuCl(2)(eta(6)-arene){(R)-PR(binaphthoxy)}] (arene = benzene (1), p-cymene (2), mesitylene (3); R = Ph (a), OPh (b), piperidyl (c)) are described. Derivatives 1-3 have been employed to promote the kinetic resolution of allylic alcohols through a redox-isomerization process. As a general trend, the best selectivities are attained with the more sterically hindered catalysts i.