Attila Bényei

Organometallic catalysis in aqueous solutions: the biphasic transfer hydrogenation of aldehydes catalyzed by water-soluble phosphine complexes of ruthenium, rhodium and iridium

Abstract Aromatic and aliphatic aldehydes can be reduced to the corresponding alcohols by hydrogen transfer from formate using, as catalysts, water-soluble complexes of Ru(II), Rh(I) and Ir(I) with monosulphonated triphenylphosphine (mSPφ)2, in aqueous/organic biphasic systems without phase transfer catalysts. HRu(O2CH)(mSPφ)2)3 was identified as the key intermediate in the processes catalyzed by RuCl2(mSPφ2)2 in an excess of phosphine. Olefinic double bonds (including those in α,β-unsaturated aldehydes), as well as substitutents of the aromatic ring, are not affected. Attempted catalysis of the transfer of benzaldehyde from the organic to the aqueous phase by β-cyclodextrin resulted in inhibition of the metal complex-catalyzed transfer hydrogenation.

Equilibrium and Kinetic Properties of the Lanthanoids(III) and Various Divalent Metal Complexes of the Heptadentate Ligand AAZTA

The heptadentate ligand 1,4-bis(hydroxycarbonylmethyl)-6-[bis(hydroxycarbonylmethyl)]amino-6-methylperhydro-1,4-diazepine (AAZTA) and its derivatives were recently reported to give stable complexes with Gd(3+) with superior efficiency as MRI contrast agents. Nevertheless, only preliminary data are available on the coordination behavior of this interesting ligand. In this work, thermodynamic and kinetic stability data are determined for the formation of complexes with AAZTA and the lanthanoid metal ions, and other divalent metal ions of interest for this application. The AAZTA ligand binds the lanthanoid ions with log K(ML) values of 17.53-21.85 with its affinity steadily increasing from La(3+) to Lu(3+), suggesting that the seven-membered skeleton is better suited to accommodate smaller metal ions. Even though the denticity is lower, the stability of the heavier lanthanoid complexes is comparable to those of the classical ligand diethylenetriaminepentaacetic acid (DTPA). The transmetalation reactions of [Gd(AAZTA)](-) with Cu(2+) and Eu(3+) predominantly occur through proton-assisted dissociation of the complex. The role of the direct attack of Cu(2+) or Eu(3+) in the exchange reactions is limited, although the formation of dinuclear complexes decreases the proton-assisted dissociation. Near physiological conditions, [Gd(AAZTA)](-) is significantly more inert than [Gd(DTPA)](2-), allowing its potentially safe use as contrast agent in magnetic resonance imaging.

Biphasic reduction of unsaturated aldehydes to unsaturated alcohols by ruthenium complex-catalyzed hydrogen transfer

Abstract Unsaturated aldehydes can be reduced under very mild conditions (30–80°C) with good yields and excellent selectivities to the corresponding unsaturated alcohols by hydrogen transfer from HCOONa/H2O catalyzed by a complex of RuII with sulphonated triphenylphosphine in aqueous/organic biphasic systems.

Base‐Induced Coupling of α‐Azido Ketones with Aldehydes − An Easy and Efficient Route to Trifunctionalized Synthons 2‐Azido‐3‐hydroxy Ketones, 2‐Acylaziridines, and 2‐Acylspiroaziridines

An improved synthesis of α-azido ketones under phase-transfer conditions has been developed. The transformation of α-azido ketones into acyclic and heterocyclic 2-azido-3-hydroxy ketones has been demonstrated and the relative configurations of the chromanone derivatives have been determined by X-ray analysis. Treatment of the aldol-type products with triphenylphosphane afforded 2-acylaziridines and the hitherto unknown spiro[chroman-3,2′-aziridin]-4-ones. The relative configuration of the spiroaziridines was determined by NOE measurements.

Molecular and crystal structure of bis(N-cyclohexyl-2-pyrrolidone)dioxouranium(VI) nitrate

Bis( N -cyclohexyl-2-pyrrolidone)dioxouranium(VI) nitrate, UO 2 (NO 3 ) 2 (NCP) 2 , has been prepared by mixing UO 2 (NO 3 ) 2 ·6H 2 O and N -cyclohexyl-2-pyrrolidone (NCP) in an aqueous nitric acid solution and characterized by NMR, IR spectroscopy, and single crystal X-ray diffractometry. The IR spectrum is consistent with typical absorption bands observed in other UO 2 (NO 3 ) 2 ·2L complexes (L=unidentate oxygen donor ligand), and supports that NCP molecule coordinates to uranium through carbonyl oxygen. The 15 N NMR spectrum shows that two structural isomers of the complex exist in inert solvents such as CD 2 Cl 2 . X-ray diffraction study reveals that average distances between uranium atom and uranyl-, nitrate-, and carbonyl- oxygen atoms are 1.748, 2.527, and 2.347 A, respectively.

Dioxane-type (2-naphthyl)methylene acetals of glycosides and their hydrogenolytic transformation into 6-O- and 4-O-(2-naphthyl)methyl (NAP) ethers

Abstract α-, β- d -Gluco-, galacto-, 2-deoxy-2-phthalimido-β- d -glucopyranosides with different aglycons (methyl, allyl, p-methoxyphenyl, thioethyl) reacted with 2-naphthaldehyde dimethyl acetal to give rise to 4,6-O-(2-naphthyl)methylene acetals. The acetals were converted into fully protected compounds bearing benzoyl, benzyl, allyl, p-methoxybenzyl groups. The fully alkylated dioxane-type acetals were hydrogenolysed with AlH3 (3LiAlH4–AlCl3) reagent to furnish 4-O-NAP/6-OH derivatives. All acetals were treated with BH3·Me3N–AlCl3 in THF and a reverse regioselectivity was observed, producing 6-O-NAP/4-OH derivatives. Similar regioselectivity was also observed by using NaCNBH3–HCl reagent. In all reactions very mild reaction conditions were required, regioselectivity was better than 93:7, and the isolated yields were between 83–92%. All compounds were characterised by 1H and 13C NMR spectra. Solid-state and solution conformation of methyl 2,3-di-O-acetyl-4,6-O-(2-naphthyl)methylene-α- d -galactopyranoside were elucidated by X-ray and NMR measurements.

VO(IV) complexes of 3-hydroxypicolinic acid: a solution study and the structure of a supramolecular assembly in the solid state

Abstract The complex formation between oxovanadium(IV) and 3-hydroxypicolinic acid (3HPA) was studied in aqueous solution and in the solid state. The ligand displays ambidentate binding properties [Polyhedron 19 (2000) 55]: it forms picolinate-type (N, COO−), salicylate-type (COO−, O−) and mixed-type complexes involving bidentate coordination of the ligand. It can also coordinate in a tridentate way, via the (N, COO−, O−) donor set, forming a tetrameric species. Two of complexes formed in equilibrium in solution were isolated in the solid state too: VOH2(3HPA)2 and [VO(3HPA)]4. The latter was characterized crystallographically; the binding mode was found to be identical in solution and in the solid state. The binding properties of the ligand were compared with those of other substituted picolinic acid derivatives. A possible relationship between the insulin-mimetic activity and the structure of these complexes is discussed.

Reactions of [Ru(H2O)6]2+ with water-soluble tertiary phosphines

In aqueous solutions under mild conditions, [Ru(H(2)O)(6)](2+) was reacted with various water-soluble tertiary phosphines. As determined by multinuclear NMR spectroscopy, reactions with the sulfonated arylphosphines L =mtppms, ptppms and mtppts yielded only the mono- and bisphosphine complexes, [Ru(H(2)O)(5)L](2+), cis-[Ru(H(2)O)(4)L(2)](2+), and trans-[Ru(H(2)O)(4)L(2)](2+) even in a high ligand excess. With the small aliphatic phosphine L = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1(3,7)]decane (pta) at [L]:[Ru]= 12:1, the tris- and tetrakisphosphino species, [Ru(H(2)O)(3)(pta)(3)](2+), [Ru(H(2)O)(2)(pta)(4)](2+), [Ru(H(2)O)(OH)(pta)(4)](+), and [Ru(OH)(2)(pta)(4)] were also detected, albeit in minor quantities. These results have significance for the in situ preparation of Ru(II)-tertiary phosphine catalysts. The structures of the complexes trans-[Ru(H(2)O)(4)(ptaMe)(2)](tos)(4)x2H(2)O, trans-[Ru(H(2)O)(4)(ptaH)(2)](tos)(4)[middle dot]2H(2)O, and trans-mer-[RuI(2)(H(2)O)(ptaMe)(3)]I(3)x2H(2)O, containing protonated or methylated pta ligands (ptaH and ptaMe, respectively) were determined by single crystal X-ray diffraction.

Solution Structures, Stabilities, Kinetics, and Dynamics of DO3A and DO3A−Sulphonamide Complexes

The Gd(3+)-DO3A-arylsulphonamide (DO3A-SA) complex is a promising pH-sensitive MRI agent. The stability constants of the DO3A-SA and DO3A complexes formed with Mg(2+), Ca(2+), Mn(2+), Zn(2+), and Cu(2+) ions are similar, whereas the logKLnL values of Ln(DO3A-SA) complexes are 2 orders of magnitude higher than those of the Ln(DO3A) complexes. The protonation constant (log KMHL) of the sulphonamide nitrogen in the Mg(2+), Ca(2+), Mn(2+), Zn(2+), and Cu(2+) complexes is very similar to that of the free ligand, whereas the logKLnHL values of the Ln(DO3A-SA) complexes are lower by about 4 logK units, indicating a strong interaction between the Ln(3+) ions and the sulphonamide N atom. The Ln(HDO3A-SA) complexes are formed via triprotonated *Ln(H3DO3A-SA) intermediates which rearrange to the final complex in an OH(-)-assisted deprotonation process. The transmetalation reaction of Gd(HDO3A-SA) with Cu(2+) is very slow (t1/2 = 5.6 × 10(3) h at pH = 7.4), and it mainly occurs through proton-assisted dissociation of the complex. The (1)H and (13)C NMR spectra of the La-, Eu-, Y-, and Lu(DO3A-SA) complexes have been assigned using 2D correlation spectroscopy (COSY, EXSY, HSQC). Two sets of signals are observed for Eu-, Y-, and Lu(DO3A-SA), showing two coordination isomers in solution, that is, square antiprismatic (SAP) and twisted square antiprismatic (TSAP) geometries with ratios of 86-14, 93-7, and 94-6%, respectively. Line shape analysis of the (13)C NMR spectra of La-, Y- , and Lu(DO3A-SA) gives higher rates and lower activation entropy values compared to Ln(DOTA) for the arm rotation, which indicates that the Ln(DO3A-SA) complexes are less rigid due to the larger flexibility of the ethylene group in the sulphonamide pendant arm. The fast isomerization and the lower activation parameters of Ln(DO3A-SA) have been confirmed by theoretical calculations in vacuo and by using the polarizable continuum model. The solid state X-ray structure of Cu(H2DO3A-SA) shows distorted octahedral coordination. The coordination sites of Cu(2+) are occupied by two ring N- and two carboxylate O-atoms in equatorial position. The other two ring N-atoms complete the coordination sphere in axial positions. The solid state structure also indicates that a carboxylate O atom and the sulphonamide nitrogen are protonated and noncoordinated.

Effect of water on the mechanism of hydrogenations catalysed by rhodium phosphine complexes

On the action of H2 in aqueous solutions, the water soluble analogue of Wilkinsons catalyst, [RhCl(tppms)3][tppmsP(C6H5)2(C6H4SO3Na)], gives [RhH(tppms)3] instead of [RhH2Cl(tppms)3] and this is reflected in the rates and selectivities of hydrogenations using this catalyst.