Gábor Besenyei

Catalytic activation of dioxygen by oximatocobalt(II) and oximatoiron(II) complexes for catecholase-mimetic oxidations of o-substituted phenols

Bis(dimethylglyoximato)cobalt(II) and -iron(II) complexes, referred to as cobaloxime(II) and ferroxime(II), respectively, containing rigid equatorial macrocycles stabilized by hydrogen bonding, are functional catecholase and phenoxazinone synthase models, but show no catechol dioxygenase type activity. We have studied the oxidation of 3,5-di-tert-butylcatechol (DBCatH2) and 2-aminophenol (AP) as model substrates with the objective of elucidating the mechanisms of these reactions, using a combination of techniques including identification of free-radical intermediates by ESR spectroscopy and UV–vis spectrophotometry of semiquinone anion radical adducts of cobaloxime and ferroxime species. Detailed kinetic studies of the catecholase-mimetic oxidations reveal a general mechanistic pattern involving reversible formation of ternary catalyst–substrate–dioxygen complexes, which are key intermediates capable of H-atom abstraction from the substrates. The resulting semiquinone anion-radical intermediate and its adducts with the catalyst complexes have been detected by ESR spectroscopy. They contain a unidentate catecholato ligand as shown by the adduct of cobaloxime(II), which has been isolated and characterized by X-ray diffraction. Our work has led to the conclusion that the lack of catechol dioxygenase activity in the case of ferroxime(II) is due to the rigid equatorial macrocycle, which prevents bidentate catechol coordination. To further test this hypothesis, we have synthesized and studied analogous iron(II) complexes with flexible quadridentate and quinquedentate dioximato Schiff-base ligands. In line with expectations, these new complexes exhibit both catecholase and catechol dioxygenase activity.

A new method for the preparation of (arylsulfonyliminoiodo)benzenes

Abstract (Arylsulfonyliminoiodo)benzenes ( 3 ) can be prepared in 52–92% yield via the reaction of dimethoxyiodobenzene ( 1 ) with the corresponding arylsulfonamide in MeOH or CH 2 Cl 2 at room temperature.

Crystallographic characterization of the palladium(I) dimers, syn-Pd2Cl2(dppmMe)2 and Pd2Cl2(dppm)2; solution conformational behavior of syn- and anti-Pd2Cl2(dppmMe)2 and their (μ-Se) adducts [dppmMe=μ-1,1-bis(diphenylphosphino)ethane, and dppm=μ-bis(diphenylphosphino)methane]

An X-ray diffraction study on syn-Pd 2 Cl 2 (dppmMe) 2 , syn-1, shows an unusual boat-like conformation of the eight-membered Pd 2 P 4 C 2 ring. This conformation, containing equatorial Me groups, facilitates access of the Pd-Pd bond to small molecules such as CO, SO 2 , and elemental sulfur or selenium, and makes the syn isomer more reactive than anti-1. A comparison of bond angles around the Pd and P atoms in the syn- and anti-isomers reveals a more strained geometry of the former, which may also contribute to the stronger propensity of syn-1 to form A-frame adducts. Solution NMR/NOE studies on syn- and anti-1 and their (μ-Se) adducts reveal the structural rigidity of these complexes; the Me groups inhibit the interchange of axial and equatorial positions on the bridging methine C-atom, and solution structures correspond to those in the solid state. The X-ray structure of Pd 2 Cl 2 (dppm) 2 is, as expected, like that of the corresponding bromo complex; both are analogous to that of anti-1 which adopts a chair conformation within both the fused, five-membered rings.

Palladium-catalyzed carbonylation of (arylsulfonyliminoiodo)benzenes to arylsulfonyl isocyanates

Abstract In the presence of palladium complexes as catalysts, carbonylation of (arylsulfonyliminoiodo)benzenes to arylsulfonyl isocyanates can be accomplished with 50–80% yield.

Carbonylation of selenilimines to arylsulfonyl isocyanates

Selenilimines of general formula ArSO2N=SePh2, 1, can be catalytically carbonylated to arylsulfonyl isocyanates, 2, in the presence of palladium complexes as catalysts. This transformation represents a new two-step oxidative N-carbonylation reaction.

Quantitative recovery of dihydrogen from hydrogen sulphide using the complexes, [Pd2X2(µ-dppm)2][X = Cl, Br, l; dppm = bis(diphenylphosphino)methane]

The complexes [Pd2X2(µ-dppm)2](1)[X = Cl, Br, I; dppm = bis(diphenylphosphino)methane] abstract sulphur from H2S under ambient conditions to form [Pd2X2(µ-S)(µ-dppm)2](2) and H2 quantitatively; (2) can be oxidized in stages to µ-SO and µ-SO2 derivatives, the latter losing SO2 spontaneously with regeneration of (1).

Vibrational spectra of monothiocarbamates. I. Assignment and tentative force field of S-methyl-N,N-dimethylthiocarbamate

Abstract FT-IR and Raman spectra of S-methyl-N,N-dimethylmonothiocarbamate and its d 3 -, d 6 -, d 9 -, and 13 C-substituted isotopomers have been recorded and analysed. Normal coordinate calculations were performed to support the assignment and to derive a simplified valence force field which would be characteristic of the monothiocarbamate moiety, =N(CO)S-, and is consistent with the known bond length vs force constant correlations.

Effect of water on the selenium catalyzed carbonylation of nitrobenzene to methyl N-phenylcarbamate

The water content of the reaction mixture exerts a marked influence on the rate of selenium catalyzed conversion of nitrobenzene to methyl N-phenyl-carbamate.AbstractСодержание воды в реакционной смеси оказывает значительный эффект на скорость превращения нитробензола в метил Н-фенилкарбамат, катализированного селениом.

N-benzoylimido complexes of palladium. Synthesis, structural characterisation and structure–reactivity relationship

Benzoyl azides, ArC(O)N3, 2, (Ar = phenyl or substituted phenyl), react with [Pd2Cl2(dppm)2], 1, [dppm = bis(diphenylphosphino)methane] with the formation of novel [Pd2Cl2(mu-NC(O)Ar)(dppm)2], 3, benzoylnitrene complexes that were structurally characterised by multinuclear magnetic resonance and IR spectroscopy and, in several instances, by single crystal X-ray diffraction. As shown by crystallographic studies, the C2P4Pd2 rings adopt extended twist-boat conformations with methylene groups bending towards the bridging benzoylimido moieties. X-ray diffraction studies have revealed the chiral nature of the imido complexes, the chiral element being the propeller-like C2P4Pd2 ring. Structural data accumulated on complexes 3 such as short C-N distances (1.32 A), elongated C=O bonds (1.30 A) as well as the outstandingly high barrier to internal rotation around the N-C(O) linkage (88.3 kJ mol(-1)) are in line with extensive ppi-ppi interaction between the bridging nitrogen and the carbonyl carbon atoms. Theoretical calculations indicate an electron shift from the dimer towards the apical nitrogen atom, which, in turn, facilitates the donation of electrons towards the carbonyl moiety. To elucidate the structure-reactivity relationship of benzoyl azides towards 1, crystallographic and solution IR spectroscopic studies were carried out on a series of para-substituted benzoyl azides. The reaction obeys the Hammett equation. The large positive value of the reaction constant indicates that the azides act as electrophiles in the reaction studied. The enhanced reactivity of 2-nitrobenzoyl azide has been attributed to a decreased conjugation of the phenyl and carbonyl moieties in this reagent.

SYNTHESIS AND CHARACTERIZATION OF NOVEL DERIVATIVES OF N-(FERROCENESULFONYL)CARBAMIC ACID. X-RAY STRUCTURE DETERMINATION OF FERROCENESULFONAMIDE AND N -(FERROCENESULFONYL)-N'-BUTYLUREA

Abstract Ferrocenesulfonamide, 1, was converted to novel N-(ferrocenesulfonyl)ureas and N-(ferrocenesulfonyl)carbamates via reacting 1 with the corresponding organic isocyanates or chloroformic acid esters. The molecular structures of 1 and N-(ferrocenesulfonyl)-N′-butylurea were determined by single-crystal X-ray diffraction. Crystal data: 1: monoclinic, P21/c, with unit cell dimensions a=12.563(1), b=9.977(2), c=8.557(1) A, and β=98.71(1)°, V=1060.2(3) A3, Z=4; 3e: orthorombic, Pbca, a=9.278(1), b=15.892(4), c=22.043(3) A, and V=3250.2(10) A3, Z=8. In both 1 and 3e, the Fe–C distances of the substituted Cp ring follow a special sequence, the Fe–C(S) bonds being shorter than the Fe–C bonds with the neighboring or remote C atoms.