Tamás Kégl

Platinum-catalysed enantioselective hydroformylation of styrene. Platinum-diphosphine-tin(II) fluoride catalytic system: a novel asymmetric hydroformylation catalyst

Abstract Enantioselective hydroformylation of styrene was carried out in the presence of platinum-containing catalysts. Tin(II) fluoride was used as cocatalyst, giving a catalytic system of unusually high stability. When the optically active diphosphine 2,4-bis(diphenylphosphino)pentane (BDPP) was used the absolute configuration of the 2-phenylpropanal formed varied with the temperature used. In dichloromethane the enantiomeric excess depends strongly on the temperature used. Although the addition of 2-diphenylphosphino-pyridine to the catalytic system strongly reduces the catalytic activity, the BDPP-2-diphenylphosphino-pyridine “mixed-phosphine system” gave 86.7% e.e.

Platinum complexes of heteroannularly bridged heterobidentate ferrocenyl diphosphine ligands: their molecular structure and their use in catalytic carbonylation reactions

Abstract Platinum complexes PtCl2(L) and PtCl(SnCl3)(L) of the ferrocenyl diphosphine ligands (L) (R,R)-1-diphenylphosphino-2,1′-[(1-diphenylphosphino)-1,3-propanediyl]-ferrocene (1), (R,R)-1-diphenylphosphino-2,1′-[(1-dicyclohexylphosphino)-1,3-propanediyl]-ferrocene (2), (R,R)-1-bis(4-fluorophenyl)phosphino-2,1′-[(1-diphenylphosphino)-1,3-propanediyl]-ferrocene (3), have been synthesised. Complexes PtCl2(1) and PtCl2(2) have been structurally characterised by X-ray diffraction. Both the ‘preformed’ and the in situ catalysts have been used in hydroformylations of styrene. At low temperature (below 70°C) and with use of the platinum catalysts the prevailing formation of (R)-2-phenyl-propanal was observed, while at higher temperatures the formation of the (S)-enantiomer was favoured. The palladium catalysts proved to be rather inactive in the hydromethoxycarbonylation of styrene. In the presence of ligand 2 the predominant formation of the linear regioisomer was observed.

Carbonylation (hydroformylation and hydroalkoxycarbonylation) of styrene in the presence of transition metal-ferrocene-based aminophosphine systems

Abstract The PtCl2(L)-type platinum complexes of the ferrocenyl ligands, (Sc,Sm)-1-diphenylphosphino-α-N,N-dimethylamino[2,3]tetramethyleneferrocene (1) and (Sc,Sm)-1,1′-bis(diphenylphosphino)-α-N,N-dimethylamino[2,3]tetramethylene ferrocene (2) have been synthesised. Both the ‘preformed’ and in situ catalysts have been used in hydroformylation of styrene. In spite of low enantioselectivities and activities, the ferrocenyl based systems proved to be of interest from theoretical point of view. The ligand influence on regio- and enantioselectivity has been investigated in systems containing either only one of the ferrocenyl ligands or one ferrocenyl ligand together with bdpp ((2S,3S)-2,4-bis(diphenylphosphino)pentane). The coordination of the respective ligands to platinum in the catalytic process can be deduced from results obtained with the ‘mixed ligand system’. The rhodium in situ catalysts containing either 1 or 2 are active in hydroformylation but the ee-s obtained with styrene are low. In the presence of ligand 1, the palladium-catalysed hydromethoxycarbonylation of styrene resulted in the predominant formation of the branched regioisomer, in case of 2 mostly the linear product was formed.

Theoretical insights into the nature of nickel-carbon dioxide interactions in Ni(PH3)2(η2-CO2).

DFT calculations were carried out for the Ni(0) complex Ni(PH(3))(2)(η(2)-CO(2)), which is a model compound for the well-known Ni(0) carbon dioxide complexes containing various tertiary phosphane ligands. The electronic structure of the complex was elucidated using domain-averaged Fermi hole (DAFH), quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), charge decomposition analysis (CDA), and natural bond orbital (NBO) methods. The carbon dioxide ligand in the complex reveals an unexpected coordination behavior. Apart from the expected π-donation interaction, the C-O σ bond takes also part in the electron donation. Moreover, the back-donation is slightly influenced by the phosphorus atom adjacent to the noncoordinated O of carbon dioxide as it transfers electron density directly to carbon. This unconventional way of back-donation may also explain the bent character of the Ni-C bond path. Due to excess kinetic energy density, no bond critical point was found between the coordinating oxygen and the nickel center. A strong relationship has been found between the DAFH and the NBO methods, which can provide additional information for the interpretation of DAFH eigenvectors.

Computational aspects of hydroformylation

The influence of transition metal complexes as catalysts upon the activity and selectivity of hydroformylation reactions has been extensively investigated during the last decades. Nowadays computational chemistry is an indispensable tool for elucidation of reaction mechanisms and for understanding the various aspects which govern the outcome of catalytic reactions. This review attempts to survey the recent literature concerning computational studies on hydroformylation and theoretical coordination chemistry results related to hydroformylation.

General Pathway of Sulfur-Chain Breakage of Polythionates by Iodine Confirmed by the Kinetics and Mechanism of the Pentathionate−Iodine Reaction

The pentathionate-iodine reaction has been studied spectrophotometrically at T = 25.0 ± 0.1 °C and at an ionic strength of 0.5 M in both the absence and presence of an initially added iodide ion at the pH range of 3.95-5.15. It was found that the pH does not affect the rate of the reaction; however, the iodide ion produced by the reaction strongly inhibits the oxidation. Therefore, it acts as an autoinhibitor. The kinetic curves also support the fact that iodide inhibition cannot be explained by the formation of the unreactive triiodide ion, and S(5)O(6)I(-) along with the iodide ion has to be involved in the initiating rapid equilibrium being shifted far to the left. Further reactions of S(5)O(6)I(-), including its hydrolysis and reaction with the iodide ion, lead to the overall stoichiometry represented by the following equation: S(5)O(6)(2-) + 10I(2) + 14H(2)O → 5SO(4)(2-) + 20I(-) + 28H(+). A nine-step kinetic model with two fitted parameters is proposed and discussed, from which a rate equation has also been derived. A brief discussion about the general pathway of sulfur-chain breakage of polythionates supported by theoretical calculations has also been included.

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.

High-pressure NMR investigation of the intermediates of platinum-phosphine hydroformylation catalysts

Abstract The reactions of square-planar alkylplatinum-diphosphine complexes, Pt(Me)(Cl)(bdpp) ( 1 ) and Pt(Me) (SnCl 3 )(bdpp) ( 2 ), as well as Pt{CH(COOEt)CH 3 (Cl)(dppp) ( 3 ) (where bdpp = (2 S ,4 S )-2,4-bis(diphenylphosphino)pentane, dppp = 1,3-bis(diphenylphosphino propane) with carbon monoxide and carbon monoxide/hydrogen mixture have been studied by high pressure NMR. Carrying out the pressurization at 273 K and the measurement of a sample containing 2 at 173 K, a methylplatinum-hydride was detected under 50 bar CO/H 2 = 1/1 pressure in CD 2 Cl 2 which was transferred to [Pt(CH 3 )(CO)(bdpp) + SnCl 3 − ( 2a ) and [Pt(COCH 3 )(CO)(bdpp] + SnCl 3 − ( 2b ) at room temperature. The platinum complex containing an alkyl stable to β-hydride elimination Pt{CH(COEOt)CH/ 3 }(Cl)(dppp) ( 3 ) was reacted with carbon monoxide resulting mainly in Pt(dppp)Cl 2 and an ionic intermediate analogous to 2a , [Pt[CH(COOEt)CH 3 ](CO)(dppp) + Cl − ( 3a ). However, the same reaction with the in situ formed SnCl 3 -inserted productm, Pt{CH(COOEt)CH 3 }(SnCl 3 )(dppp) yielded [Pt(CH 3 )(CO)(dppp)] + SnCl 3 − ( 4a ) as a minor component besides PtCl 2 (dppp) and the decomposition product Pt(Me)(Cl)(dppp) ( 1′ ).

Synthesis of ferrocene-labeled steroids via copper-catalyzed azide-alkyne cycloaddition. Reactivity difference between 2β-, 6β- and 16β-azido-androstanes

Copper-catalyzed cycloaddition of steroidal azides and ferrocenyl-alkynes were found to be an efficient methodology for the synthesis of ferrocene-labeled steroids. At the same time, a great difference between the reactivity of 2β- or 16β-azido-androstanes and a sterically hindered 6β-azido steroid toward both ferrocenyl-alkynes and simple alkynes, such as phenylacetylene, 1-octyne, propargyl acetate and methyl propiolate, was observed.

Facile, high-yielding synthesis of deepened cavitands: A synthetic and theoretical study

A wide variety of 2-methyl-resorcinol-based deepened cavitands were synthesised from readily available reagents in a four-step procedure with overall yields of up to 62%. A systematic variation of the rim was carried out by building up a flexible upper aromatic wall on the rigid cavitand platform through CH2, CH2O and CH2OCH2 spacers. These aromatic walls were further extended by a Suzuki cross-coupling reaction. Full characterisation of the synthesised cavitands was carried out. The solid-state structure of tetrakis(phenoxymethyl)cavitand was determined by X-ray crystallography. Gas-phase theoretical calculations for this molecule predict the presence of weak T-shaped interactions between the upper phenyl rings. The host–guest complex formation ability of two deepened cavitand hosts towards 4-chloro-benzotrifluoride was proved by photoluminescence method.