Gábor Szalontai

Catalytic and structural studies of RhI complexes of (−)-(2S,4S)-2,4-bis(diphenylphosphino)pentane. Asymmetric hydrogenation of acetophenonebenzylimine and acetophenone

Abstract Rhodium(I) complexes formed by (−)-(2 S ,4 S )-2,4-bis(diphenylphosphino)pentane (BDPP) are efficient catalysts for the hydrogenation of acetophenone and acetophenonebenzylimine. The composition of the solvent mixture and the reaction temperature have a marked influenced on the enantioselectivity. These effects are thought to be related to the enhanced conformational flexibility of six-membered rings when simple substrates without functional groups are coordinated to the rhodium. X-ray crystallographic studies reveal that in [Rh(( S , S )-BDPP)NBD] + ( 1 ) the ligand is in a chair conformation, and that in [Rh(( S , S )-BDPP)COD] + ( 2 ) the chelate ring is in a δ-skew conformation. Studies of Rh(( S , S )-BDPP)(NBD)Cl ( 3 ) in solution indicate a trigonal bipyramidal structure with a chair conformation of the ring in aromatic solvents and a conformationally labile ring in methanol.

Temperature dependence of the enantioselective hydroformylation with PtCl2[(S)-BINAP] + SnCl2 catalyst and the dynamic NMR study of the catalytic precursor

Abstract The strong temperature dependence of the absolute configuration of the α-phenylpropanal formed in the PtCl2[(S)-BINAP]-catalysed hydroformylation (BINAP=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) of styrene is explained by the restricted rotation of the phenyl rings on the basis of a dynamic NMR study.

Carbonylation (hydroformylation and hydrocarbalkoxylation) reactions in the presence of transition metal: p-tert-butyl-calix[4]arene-based phosphine and phosphinite systems

Abstract In this study, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-diphenylphosphinoxy-ethoxy)calix[4]arene (5) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-diphenylphosphinoethoxy)-calix[4]arene (6), as well as their platinum and palladium complexes (PtCl2)2(5), (PdCl2)2(5) were synthesised and characterised. In addition to these transition metal-containing complexes the catalytic systems formed in situ, from catalytic precursors PtCl2(PhCN)2, [Rh(nbd)Cl]2 and PdCl2(PhCN)2 and the corresponding calixarene ligand, were tested as catalysts in hydroformylation and hydrocarbalkoxylation, respectively. High chemoselectivity was obtained in hydroformylation in the presence of rhodium-containing catalysts both with the above calixarene-based phosphine and phosphinite ligands. The regioselectivity towards branched aldehyde shows a strong temperature dependence in case of phosphinite derivative. Although the platinum-containing systems show much lower catalytic activity, the regioselectivities are undoubtedly higher than those obtained with PtCl2(diphosphine)–SnCl2 systems.

Hydroformylation of chiral terpenes with PtCl(SnCl3)-(bis-phosphine) as catalyst

Abstract (+)- R -Limonene and (−)- R -carvone undergo hydroformylation in the presence of catalytic Pt-bisphosphine-SnCl 2 systems to yield exclusively the linear products. The internal double bond and the carbonyl group remain intact in both substrates during the reaction. The variation of the diastereomeric composition of the aldehydes upon variation of the chelating phosphine in the catalyst has been investigated.

The role of additives in platinum-catalyzed hydroformylation

Abstract A study has been made of hydroformylation of styrene derivatives catalysed by several Pt—bisphosphine systems modified with various additives. The chain length of the chelating phosphines and the quality of the Lewis-acid type additives strongly influences the activity and the chemo- and regio-selectivity of the catalysts. The most active PtCl 2 (bisphosphine) + SnCl 2 system was modified with amines of different basicities, and it was found that a strong base such as Et 3 N stops the catalytic reaction by abstracting HSnCl 3 from the active platinum species. This reaction was monitored by NMR spectroscopy. Complexation of the chiral aminophosphine (( S )-(−)- N , N -dimethyl-1(2′-diphenylphosphinophenyl)-ethylamine, ( S )-(−)-AMPHOS) with platinum has also been studied, and a chemical shift anisotropy relaxation mechanism observed.

Homogeneous catalytic dehalodimerization of 17-iodo-Δ16 steroids

Abstract 17-Iodo- Δ 16 steroids undergo selective dimerization and carbonylative dimerization in the presence of palladium catalysts in dimethylformamide which result in 16–17′-coupled dienes and 17-carboxylic anhydrides, respectively. Moderate to good yields have been obtained for both types of dimers.

A study on the catalytic pathways of the hydroalkoxycarbonylation reaction of styrene

Abstract The catalytic pathways of the Pd(PPh 3 ) 2 Cl 2 /SnCl 2 -catalysed styrene hydroalkoxycarbonylation reaction have been elucidated. Using deuterium labelling, the different reaction products were detected by mass spectral analysis and the deuterium content and its distribution determined by 1 H-, 2 H- and 13 C-NMR methods. The great number of labelled species supports the assumption that the hydrido (Pd–H) route is the operating mechanism of this system. Alkyl–metal intermediates easily undergo β-hydride elimination. This process is reversible for both isomers even at low reaction temperature

New [PtCl(monophosphine)(chiral bisphosphine)]+ cations

Abstract [PtCl(P)(PP)]+ cations (P monodentate, P-P bidentate tertiary phosphines) have been derived quantitatively from PtCl2(PP) and monophosphines in the presence of SnCl2, and characterised by 31P NMR spectroscopy and conductivity measurements.

Comparative analysis of zaleplon complexation with cyclodextrins and hydrophilic polymers in solution and in solid state

The aim of this work was to investigate the potential synergistic effect of water-soluble polymers (hypromellose, HPMC and polyvinylpyrrolidone, PVP) on zaleplon (ZAL) complexation with parent β-cyclodextrin (βCD) and its randomly methylated derivative (RAMEB) in solution and in solid state. The addition of HPMC to the complexation medium improved ZAL complexation and solubilization with RAMEB (K(ZAL/RAMEB)=156±5M(-1) and K(ZAL/RAMEB/HPMC)=189±8M(-1); p<0.01), while such effect was not observed for βCD (K(ZAL/βCD)=112±2M(-1) and K(ZAL/βCD/HPMC)=119±8M(-1); p>0.05). Although PVP increased the ZAL aqueous solubility from 0.22 to 0.27mg/mL, it did not show any synergistic effects on ZAL solubilization with the cyclodextrins tested. Binary and ternary systems of ZAL with βCD, RAMEB and HPMC were prepared by spray-drying. Differential scanning calorimetry, X-ray powder diffraction and scanning electron microscopy demonstrated a partial ZAL amorphization in spray-dried binary and ternary systems with βCD, while the drug was completely amorphous in all samples with RAMEB. Furthermore, inclusion complex formation in all systems prepared was confirmed by solid-state NMR spectroscopy. The in vitro dissolution rate followed the rank order ZAL/RAMEB/HPMC>ZAL/RAMEB=ZAL/βCD/HPMC>ZAL/βCD≫ZAL, clearly demonstrating the superior performance of RAMEB on ZAL complexation in the solid state and its synergistic effect with HPMC on drug solubility. Surprisingly, when loaded into tablets made with insoluble microcrystalline cellulose, RAMEB complexes had no positive effect on drug dissolution, because HPMC and RAMEB acted as a binders inside the tablets, prolonging their disintegration. Oppositely, the formulation with mannitol, a soluble excipient, containing a ternary RAMEB system, released the complete drug-dose in only 5min, clearly demonstrating its suitability for the development of immediate-release oral formulation of ZAL.

Novel diphosphine platinum cations: NMR and Mössbauer spectra and catalytic studies

Abstract The reaction of PtCl2(diphosphine) with mono and bidentate phosphines has been investigated by NMR spectroscopy. [Pt(diphosphine) (PMe3)2]2+, [Pt(diphosphine)2]2+ and [Pt((S,S)-bdpp)((S,S)-chiraphos)]2+ cations have been characterized by 31P NMR and conductivity measurements. The presence of tin(II) chloride promotes the formation of the complex cations. Evidence for coordination of the diphosphine in monodentate mode has benn obtained by NMR spectroscopy. The platinum species possessing a platinum-tin bond and ionic complexes with an SnCl3− counterion can easily be distinguished by 119Sn Mossbauer spectroscopy. Asymmetric hydroformylation of styrene with [Pt((S,S)-bdpp)2]2+(SnCl3−)2 as catalyst precursor gave chemo-, regio- and enantio-selectivities different from those obtained with the covalent PtCl(SnCl3)((S,S)-bdpp) as catalyst precursor.